man pages section 1: User Commands

Exit Print View

Updated: July 2014

perltodo (1)


perltodo - DO List


Please see following description for synopsis


Perl Programmers Reference Guide                      PERLTODO(1)

     perltodo - Perl TO-DO List

     This is a list of wishes for Perl. The most up to date
     version of this file is at

     The tasks we think are smaller or easier are listed first.
     Anyone is welcome to work on any of these, but it's a good
     idea to first contact to avoid
     duplication of effort, and to learn from any previous
     attempts. By all means contact a pumpking privately first if
     you prefer.

     Whilst patches to make the list shorter are most welcome,
     ideas to add to the list are also encouraged. Check the
     perl5-porters archives for past ideas, and any discussion
     about them. One set of archives may be found at:

     What can we offer you in return? Fame, fortune, and
     everlasting glory? Maybe not, but if your patch is
     incorporated, then we'll add your name to the AUTHORS file,
     which ships in the official distribution. How many other
     programming languages offer you 1 line of immortality?

Tasks that only need Perl knowledge
  Improve Porting/ to work from git tags
     See Porting/release_managers_guide.pod for a bit more

  Migrate t/ from custom TAP generation
     Many tests below t/ still generate TAP by "hand", rather
     than using library functions. As explained in "Writing a
     test" in perlhack, tests in t/ are written in a particular
     way to test that more complex constructions actually work
     before using them routinely. Hence they don't use
     "Test::More", but instead there is an intentionally simpler
     library, t/ However, quite a few tests in t/ have
     not been refactored to use it. Refactoring any of these
     tests, one at a time, is a useful thing TODO.

     The subdirectories base, cmd and comp, that contain the most
     basic tests, should be excluded from this task.

  Test that was run
     There are various generated files shipped with the perl
     distribution, for things like header files generate from
     data. The generation scripts are written in perl, and all
     can be run by However, because they're written in

perl v5.12.5         Last change: 2012-11-03                    1

Perl Programmers Reference Guide                      PERLTODO(1)

     perl, we can't run them before we've built perl. We can't
     run them as part of the Makefile, because changing files
     underneath make confuses it completely, and we don't want to
     run them automatically anyway, as they change files shipped
     by the distribution, something we seek not do to.

     If someone changes the data, but forgets to re-run
     then the generated files are out of sync. It would be good
     to have a test in t/porting that checks that the generated
     files are in sync, and fails otherwise, to alert someone
     before they make a poor commit. I suspect that this would
     require adapting the scripts run from to have dry-
     run options, and invoking them with these, or by refactoring
     them into a library that does the generation, which can be
     called by the scripts, and by the test.

  Automate perldelta generation
     The perldelta file accompanying each release summaries the
     major changes.  It's mostly manually generated currently,
     but some of that could be automated with a bit of perl,
     specifically the generation of

     Modules and Pragmata
     New Documentation
     New Tests

     See Porting/how_to_write_a_perldelta.pod for details.

  Remove duplication of test setup.
     Schwern notes, that there's duplication of code - lots and
     lots of tests have some variation on the big block of
     $Is_Foo checks.  We can safely put this into a file, change
     it to build an %Is hash and require it.  Maybe just put it
     into Throw in the handy tainting subroutines.

  POD -> HTML conversion in the core still sucks
     Which is crazy given just how simple POD purports to be, and
     how simple HTML can be. It's not actually as simple as it
     sounds, particularly with the flexibility POD allows for
     "=item", but it would be good to improve the visual appeal
     of the HTML generated, and to avoid it having any validation
     errors. See also "make HTML install work", as the layout of
     installation tree is needed to improve the cross-linking.

     The addition of "Pod::Simple" and its related modules may
     make this task easier to complete.

  Make ExtUtils::ParseXS use strict;
     lib/ExtUtils/ contains this line

         # use strict;  # One of these days...

perl v5.12.5         Last change: 2012-11-03                    2

Perl Programmers Reference Guide                      PERLTODO(1)

     Simply uncomment it, and fix all the resulting issues :-)

     The more practical approach, to break the task down into
     manageable chunks, is to work your way though the code from
     bottom to top, or if necessary adding extra "{ ... }"
     blocks, and turning on strict within them.

  Make Schwern poorer
     We should have tests for everything. When all the core's
     modules are tested, Schwern has promised to donate to $500
     to TPF. We may need volunteers to hold him upside down and
     shake vigorously in order to actually extract the cash.

  Improve the coverage of the core tests
     Use Devel::Cover to ascertain the core modules' test
     coverage, then add tests that are currently missing.

  test B
     A full test suite for the B module would be nice.

  A decent benchmark
     "perlbench" seems impervious to any recent changes made to
     the perl core. It would be useful to have a reasonable
     general benchmarking suite that roughly represented what
     current perl programs do, and measurably reported whether
     tweaks to the core improve, degrade or don't really affect
     performance, to guide people attempting to optimise the guts
     of perl. Gisle would welcome new tests for perlbench.

  fix tainting bugs
     Fix the bugs revealed by running the test suite with the
     "-t" switch (via "make test.taintwarn").

  Dual life everything
     As part of the "dists" plan, anything that doesn't belong in
     the smallest perl distribution needs to be dual lifed.
     Anything else can be too. Figure out what changes would be
     needed to package that module and its tests up for CPAN, and
     do so. Test it with older perl releases, and fix the
     problems you find.

     To make a minimal perl distribution, it's useful to look at

  Move dual-life pod/*.PL into ext
     Nearly all the dual-life modules have been moved to ext.
     However, we still  need to move pod/*.PL into their
     respective directories in ext/. They're referenced by (at
     least) "plextract" in Makefile.SH and "utils" in
     win32/Makefile and win32/, and listed explicitly
     in win32/pod.mak, vms/descrip_mms.template and utils.lst

perl v5.12.5         Last change: 2012-11-03                    3

Perl Programmers Reference Guide                      PERLTODO(1)

  POSIX memory footprint
     Ilya observed that use POSIX; eats memory like there's no
     tomorrow, and at various times worked to cut it down. There
     is probably still fat to cut out - for example POSIX passes
     Exporter some very memory hungry data structures.
     There is a script that generates several header
     files to prefix all of Perl's symbols in a consistent way,
     to provide some semblance of namespace support in "C".
     Functions are declared in embed.fnc, variables in
     interpvar.h. Quite a few of the functions and variables are
     conditionally declared there, using "#ifdef". However, doesn't understand the C macros, so the rules about
     which symbols are present when is duplicated in
     Writing things twice is bad, m'kay.  It would be good to
     teach "" to understand the conditional compilation,
     and hence remove the duplication, and the mistakes it has

  use strict; and AutoLoad
     Currently if you write

         package Whack;
         use AutoLoader 'AUTOLOAD';
         use strict;
         sub bloop {
             print join (' ', No, strict, here), "!\n";

     then "use strict;" isn't in force within the autoloaded
     subroutines. It would be more consistent (and less
     surprising) to arrange for all lexical pragmas in force at
     the __END__ block to be in force within each autoloaded

     There's a similar problem with SelfLoader.

  profile installman
     The installman script is slow. All it is doing text
     processing, which we're told is something Perl is good at.
     So it would be nice to know what it is doing that is taking
     so much CPU, and where possible address it.

  enable lexical enabling/disabling of inidvidual warnings
     Currently, warnings can only be enabled or disabled by
     category. There are times when it would be useful to quash a
     single warning, not a whole category.

perl v5.12.5         Last change: 2012-11-03                    4

Perl Programmers Reference Guide                      PERLTODO(1)

Tasks that need a little sysadmin-type knowledge
     Or if you prefer, tasks that you would learn from, and
     broaden your skills base...

  make HTML install work
     There is an "installhtml" target in the Makefile. It's
     marked as "experimental". It would be good to get this
     tested, make it work reliably, and remove the "experimental"
     tag. This would include

     1.  Checking that cross linking between various parts of the
         documentation works.  In particular that links work
         between the modules (files with POD in lib/) and the
         core documentation (files in pod/)

     2.  Work out how to split "perlfunc" into chunks, preferably
         one per function group, preferably with general case
         code that could be used elsewhere.  Challenges here are
         correctly identifying the groups of functions that go
         together, and making the right named external cross-
         links point to the right page. Things to be aware of are
         "-X", groups such as "getpwnam" to "endservent", two or
         more "=items" giving the different parameter lists, such

             =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
             =item substr EXPR,OFFSET,LENGTH
             =item substr EXPR,OFFSET

         and different parameter lists having different meanings.
         (eg "select")

  compressed man pages
     Be able to install them. This would probably need a
     configure test to see how the system does compressed man
     pages (same directory/different directory?  same
     filename/different filename), as well as tweaking the
     installman script to compress as necessary.

  Add a code coverage target to the Makefile
     Make it easy for anyone to run Devel::Cover on the core's
     tests. The steps to do this manually are roughly

     o   do a normal "Configure", but include Devel::Cover as a
         module to install (see INSTALL for how to do this)


             make perl


perl v5.12.5         Last change: 2012-11-03                    5

Perl Programmers Reference Guide                      PERLTODO(1)

             cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness

     o   Process the resulting Devel::Cover database

     This just give you the coverage of the .pms. To also get the
     C level coverage you need to

     o   Additionally tell "Configure" to use the appropriate C
         compiler flags for "gcov"


             make perl.gcov

         (instead of "make perl")

     o   After running the tests run "gcov" to generate all the
         .gcov files.  (Including down in the subdirectories of

     o   (From the top level perl directory) run "gcov2perl" on
         all the ".gcov" files to get their stats into the
         cover_db directory.

     o   Then process the Devel::Cover database

     It would be good to add a single switch to "Configure" to
     specify that you wanted to perform perl level coverage, and
     another to specify C level coverage, and have "Configure"
     and the Makefile do all the right things automatically.

  Make cope with differences between built and
     installed perl
     Quite often vendors ship a perl binary compiled with their
     (pay-for) compilers.  People install a free compiler, such
     as gcc. To work out how to build extensions, Perl
     interrogates %Config, so in this situation %Config describes
     compilers that aren't there, and extension building fails.
     This forces people into choosing between re-compiling perl
     themselves using the compiler they have, or only using
     modules that the vendor ships.

     It would be good to find a way teach "" about the
     installation setup, possibly involving probing at install
     time or later, so that the %Config in a binary distribution
     better describes the installed machine, when the installed
     machine differs from the build machine in some significant

  linker specification files
     Some platforms mandate that you provide a list of a shared
     library's external symbols to the linker, so the core

perl v5.12.5         Last change: 2012-11-03                    6

Perl Programmers Reference Guide                      PERLTODO(1)

     already has the infrastructure in place to do this for
     generating shared perl libraries. My understanding is that
     the GNU toolchain can accept an optional linker
     specification file, and restrict visibility just to symbols
     declared in that file. It would be good to extend
     to support this format, and to provide a means within
     "Configure" to enable it. This would allow Unix users to
     test that the export list is correct, and to build a perl
     that does not pollute the global namespace with private

  Cross-compile support
     Currently "Configure" understands "-Dusecrosscompile"
     option. This option arranges for building "miniperl" for
     TARGET machine, so this "miniperl" is assumed then to be
     copied to TARGET machine and used as a replacement of full
     "perl" executable.

     This could be done little differently. Namely "miniperl"
     should be built for HOST and then full "perl" with
     extensions should be compiled for TARGET.  This, however,
     might require extra trickery for %Config: we have one config
     first for HOST and then another for TARGET.  Tools like
     MakeMaker will be mightily confused.  Having around two
     different types of executables and libraries (HOST and
     TARGET) makes life interesting for Makefiles and shell (and
     Perl) scripts.  There is $Config{run}, normally empty, which
     can be used as an execution wrapper.  Also note that in some
     cross-compilation/execution environments the HOST and the
     TARGET do not see the same filesystem(s), the $Config{run}
     may need to do some file/directory copying back and forth.

     Make pod/roffitall be updated by pod/buildtoc.

  Split "linker" from "compiler"
     Right now, Configure probes for two commands, and sets two

     o   "cc" (in cc.U)

         This variable holds the name of a command to execute a C
         compiler which can resolve multiple global references
         that happen to have the same name.  Usual values are cc
         and gcc.  Fervent ANSI compilers may be called c89.  AIX
         has xlc.

     o   "ld" (in dlsrc.U)

         This variable indicates the program to be used to link
         libraries for dynamic loading.  On some systems, it is
         ld.  On ELF systems, it should be $cc.  Mostly, we'll

perl v5.12.5         Last change: 2012-11-03                    7

Perl Programmers Reference Guide                      PERLTODO(1)

         try to respect the hint file setting.

     There is an implicit historical assumption from around
     Perl5.000alpha something, that $cc is also the correct
     command for linking object files together to make an
     executable. This may be true on Unix, but it's not true on
     other platforms, and there are a maze of work arounds in
     other places (such as Makefile.SH) to cope with this.

     Ideally, we should create a new variable to hold the name of
     the executable linker program, probe for it in Configure,
     and centralise all the special case logic there or in hints

     A small bikeshed issue remains - what to call it, given that
     $ld is already taken (arguably for the wrong thing now, but
     on SunOS 4.1 it is the command for creating dynamically-
     loadable modules) and $link could be confused with the Unix
     command line executable of the same name, which does
     something completely different. Andy Dougherty makes the
     counter argument "In parrot, I tried to call the command
     used to link object files and  libraries into an executable
     link, since that's what my vaguely-remembered DOS and VMS
     experience suggested. I don't think any real confusion has
     ensued, so it's probably a reasonable name for perl5 to

     "Alas, I've always worried that introducing it would make
     things worse, since now the module building utilities would
     have to look for $Config{link} and institute a fall-back
     plan if it weren't found."  Although I can see that as
     confusing, given that $Config{d_link} is true when (hard)
     links are available.

  Configure Windows using PowerShell
     Currently, Windows uses hard-coded config files based to
     build the config.h for compiling Perl.  Makefiles are also
     hard-coded and need to be hand edited prior to building
     Perl. While this makes it easy to create a perl.exe that
     works across multiple Windows versions, being able to
     accurately configure a perl.exe for a specific Windows
     versions and VS C++ would be a nice enhancement.  With
     PowerShell available on Windows XP and up, this may now be
     possible.  Step 1 might be to investigate whether this is
     possible and use this to clean up our current makefile
     situation.  Step 2 would be to see if there would be a way
     to use our existing metaconfig units to configure a Windows
     Perl or whether we go in a separate direction and make it
     so.  Of course, we all know what step 3 is.

  decouple -g and -DDEBUGGING
     Currently Configure automatically adds "-DDEBUGGING" to the

perl v5.12.5         Last change: 2012-11-03                    8

Perl Programmers Reference Guide                      PERLTODO(1)

     C compiler flags if it spots "-g" in the optimiser flags.
     The pre-processor directive "DEBUGGING" enables perl's
     command line "-D" options, but in the process makes perl
     slower. It would be good to disentangle this logic, so that
     C-level debugging with "-g" and Perl level debugging with
     "-D" can easily be enabled independently.

Tasks that need a little C knowledge
     These tasks would need a little C knowledge, but don't need
     any specific background or experience with XS, or how the
     Perl interpreter works

  Weed out needless PERL_UNUSED_ARG
     The C code uses the macro "PERL_UNUSED_ARG" to stop
     compilers warning about unused arguments. Often the
     arguments can't be removed, as there is an external
     constraint that determines the prototype of the function, so
     this approach is valid. However, there are some cases where
     "PERL_UNUSED_ARG" could be removed. Specifically

     o   The prototypes of (nearly all) static functions can be

     o   Unused arguments generated by short cut macros are
         wasteful - the short cut macro used can be changed.

  Modernize the order of directories in @INC
     The way @INC is laid out by default, one cannot upgrade core
     (dual-life) modules without overwriting files. This causes
     problems for binary package builders.  One possible proposal
     is laid out in this message:

     Natively 64-bit systems need neither -Duse64bitint nor
     -Duse64bitall.  On these systems, it might be the default
     compilation mode, and there is currently no guarantee that
     passing no use64bitall option to the Configure process will
     build a 32bit perl. Implementing -Duse32bit* options would
     be nice for perl 5.12.

  Profile Perl - am I hot or not?
     The Perl source code is stable enough that it makes sense to
     profile it, identify and optimise the hotspots. It would be
     good to measure the performance of the Perl interpreter
     using free tools such as cachegrind, gprof, and dtrace, and
     work to reduce the bottlenecks they reveal.

     As part of this, the idea of pp_hot.c is that it contains
     the hot ops, the ops that are most commonly used. The idea

perl v5.12.5         Last change: 2012-11-03                    9

Perl Programmers Reference Guide                      PERLTODO(1)

     is that by grouping them, their object code will be adjacent
     in the executable, so they have a greater chance of already
     being in the CPU cache (or swapped in) due to being near
     another op already in use.

     Except that it's not clear if these really are the most
     commonly used ops. So as part of exercising your skills with
     coverage and profiling tools you might want to determine
     what ops really are the most commonly used. And in turn
     suggest evictions and promotions to achieve a better

     One piece of Perl code that might make a good testbed is

  Allocate OPs from arenas
     Currently all new OP structures are individually malloc()ed
     and free()d.  All "malloc" implementations have space
     overheads, and are now as fast as custom allocates so it
     would both use less memory and less CPU to allocate the
     various OP structures from arenas. The SV arena code can
     probably be re-used for this.

     Note that Configuring perl with
     "-Accflags=-DPL_OP_SLAB_ALLOC" will use Perl_Slab_alloc() to
     pack optrees into a contiguous block, which is probably
     superior to the use of OP arenas, esp. from a cache locality
     standpoint.  See "Profile Perl - am I hot or not?".

  Improve win32/wince.c
     Currently, numerous functions look virtually, if not
     completely, identical in both "win32/wince.c" and
     "win32/win32.c" files, which can't be good.

  Use secure CRT functions when building with VC8 on Win32
     Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT
     functions on the basis that they were "unsafe" and
     introduced differently named secure versions of them as
     replacements, e.g. instead of writing

         FILE* f = fopen(__FILE__, "r");

     one should now write

         FILE* f;
         errno_t err = fopen_s(&f, __FILE__, "r");

     Currently, the warnings about these deprecations have been
     disabled by adding -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS.
     It would be nice to remove that warning suppressant and
     actually make use of the new secure CRT functions.

perl v5.12.5         Last change: 2012-11-03                   10

Perl Programmers Reference Guide                      PERLTODO(1)

     There is also a similar issue with POSIX CRT function names
     like fileno having been deprecated in favour of ISO C++
     conformant names like _fileno. These warnings are also
     currently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE.
     It might be nice to do as Microsoft suggest here too,
     although, unlike the secure functions issue, there is
     presumably little or no benefit in this case.

  Fix POSIX::access() and chdir() on Win32
     These functions currently take no account of DACLs and
     therefore do not behave correctly in situations where access
     is restricted by DACLs (as opposed to the read-only

     Furthermore, POSIX::access() behaves differently for
     directories having the read-only attribute set depending on
     what CRT library is being used. For example, the _access()
     function in the VC6 and VC7 CRTs (wrongly) claim that such
     directories are not writable, whereas in fact all
     directories are writable unless access is denied by DACLs.
     (In the case of directories, the read-only attribute
     actually only means that the directory cannot be deleted.)
     This CRT bug is fixed in the VC8 and VC9 CRTs (but, of
     course, the directory may still not actually be writable if
     access is indeed denied by DACLs).

     For the chdir() issue, see ActiveState bug #74552:

     Therefore, DACLs should be checked both for consistency
     across CRTs and for the correct answer.

     (Note that perl's -w operator should not be modified to
     check DACLs. It has been written so that it reflects the
     state of the read-only attribute, even for directories
     (whatever CRT is being used), for symmetry with chmod().)

  strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()

     Maybe create a utility that checks after each libperl.a
     creation that none of the above (nor sprintf(), vsprintf(),
     or *SHUDDER* gets()) ever creep back to libperl.a.

       nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'

     Note, of course, that this will only tell whether your
     platform is using those naughty interfaces.

  -D_FORTIFY_SOURCE=2, -fstack-protector
     Recent glibcs support "-D_FORTIFY_SOURCE=2" and recent gcc
     (4.1 onwards?) supports "-fstack-protector", both of which
     give protection against various kinds of buffer overflow

perl v5.12.5         Last change: 2012-11-03                   11

Perl Programmers Reference Guide                      PERLTODO(1)

     problems.  These should probably be used for compiling Perl
     whenever available, Configure and/or hints files should be
     adjusted to probe for the availability of these features and
     enable them as appropriate.

  Arenas for GPs? For MAGIC?
     "struct gp" and "struct magic" are both currently allocated
     by "malloc".  It might be a speed or memory saving to change
     to using arenas. Or it might not. It would need some
     suitable benchmarking first. In particular, "GP"s can
     probably be changed with minimal compatibility impact
     (probably nothing outside of the core, or even outside of
     gv.c allocates them), but they probably aren't
     allocated/deallocated often enough for a speed saving.
     Whereas "MAGIC" is allocated/deallocated more often, but in
     turn, is also something more externally visible, so changing
     the rules here may bite external code.

  Shared arenas
     Several SV body structs are now the same size, notably PVMG
     and PVGV, PVAV and PVHV, and PVCV and PVFM. It should be
     possible to allocate and return same sized bodies from the
     same actual arena, rather than maintaining one arena for
     each. This could save 4-6K per thread, of memory no longer
     tied up in the not-yet-allocated part of an arena.

Tasks that need a knowledge of XS
     These tasks would need C knowledge, and roughly the level of
     knowledge of the perl API that comes from writing modules
     that use XS to interface to C.

  Write an XS cookbook
     Create pod/perlxscookbook.pod with short, task-focused
     'recipes' in XS that demonstrate common tasks and good
     practices.  (Some of these might be extracted from
     perlguts.) The target audience should be XS novices, who
     need more examples than perlguts but something less
     overwhelming than perlapi.  Recipes should provide "one
     pretty good way to do it" instead of TIMTOWTDI.

     Rather than focusing on interfacing Perl to C libraries,
     such a cookbook should probably focus on how to optimize
     Perl routines by re-writing them in XS.  This will likely be
     more motivating to those who mostly work in Perl but are
     looking to take the next step into XS.

     Deconstructing and explaining some simpler XS modules could
     be one way to bootstrap a cookbook.  (List::Util?
     Class::XSAccessor? Tree::Ternary_XS?)  Another option could
     be deconstructing the implementation of some simpler
     functions in op.c.

perl v5.12.5         Last change: 2012-11-03                   12

Perl Programmers Reference Guide                      PERLTODO(1)

  Allow XSUBs to inline themselves as OPs
     For a simple XSUB, often the subroutine dispatch takes more
     time than the XSUB itself. The tokeniser already has the
     ability to inline constant subroutines - it would be good to
     provide a way to inline other subroutines.

     Specifically, simplest approach looks to be to allow an XSUB
     to provide an alternative implementation of itself as a
     custom OP. A new flag bit in "CvFLAGS()" would signal to the
     peephole optimiser to take an optree such as this:

         b  <@> leave[1 ref] vKP/REFC ->(end)
         1     <0> enter ->2
         2     <;> nextstate(main 1 -e:1) v:{ ->3
         a     <2> sassign vKS/2 ->b
         8        <1> entersub[t2] sKS/TARG,1 ->9
         -           <1> ex-list sK ->8
         3              <0> pushmark s ->4
         4              <$> const(IV 1) sM ->5
         6              <1> rv2av[t1] lKM/1 ->7
         5                 <$> gv(*a) s ->6
         -              <1> ex-rv2cv sK ->-
         7                 <$> gv(*x) s/EARLYCV ->8
         -        <1> ex-rv2sv sKRM*/1 ->a
         9           <$> gvsv(*b) s ->a

     perform the symbol table lookup of "rv2cv" and "gv(*x)",
     locate the pointer to the custom OP that provides the direct
     implementation, and re- write the optree something like:

         b  <@> leave[1 ref] vKP/REFC ->(end)
         1     <0> enter ->2
         2     <;> nextstate(main 1 -e:1) v:{ ->3
         a     <2> sassign vKS/2 ->b
         7        <1> custom_x -> 8
         -           <1> ex-list sK ->7
         3              <0> pushmark s ->4
         4              <$> const(IV 1) sM ->5
         6              <1> rv2av[t1] lKM/1 ->7
         5                 <$> gv(*a) s ->6
         -              <1> ex-rv2cv sK ->-
         -                 <$> ex-gv(*x) s/EARLYCV ->7
         -        <1> ex-rv2sv sKRM*/1 ->a
         8           <$> gvsv(*b) s ->a

     i.e. the gv(*) OP has been nulled and spliced out of the
     execution path, and the "entersub" OP has been replaced by
     the custom op.

     This approach should provide a measurable speed up to simple
     XSUBs inside tight loops. Initially one would have to write
     the OP alternative implementation by hand, but it's likely

perl v5.12.5         Last change: 2012-11-03                   13

Perl Programmers Reference Guide                      PERLTODO(1)

     that this should be reasonably straightforward for the type
     of XSUB that would benefit the most. Longer term, once the
     run-time implementation is proven, it should be possible to
     progressively update ExtUtils::ParseXS to generate OP
     implementations for some XSUBs.

  Remove the use of SVs as temporaries in dump.c
     dump.c contains debugging routines to dump out the contains
     of perl data structures, such as "SV"s, "AV"s and "HV"s.
     Currently, the dumping code uses "SV"s for its temporary
     buffers, which was a logical initial implementation choice,
     as they provide ready made memory handling.

     However, they also lead to a lot of confusion when it
     happens that what you're trying to debug is seen by the code
     in dump.c, correctly or incorrectly, as a temporary scalar
     it can use for a temporary buffer. It's also not possible to
     dump scalars before the interpreter is properly set up, such
     as during ithreads cloning. It would be good to
     progressively replace the use of scalars as string
     accumulation buffers with something much simpler, directly
     allocated by "malloc". The dump.c code is (or should be)
     only producing 7 bit US-ASCII, so output character sets are
     not an issue.

     Producing and proving an internal simple buffer allocation
     would make it easier to re-write the internals of the PerlIO
     subsystem to avoid using "SV"s for its buffers, use of which
     can cause problems similar to those of dump.c, at similar

  safely supporting POSIX SA_SIGINFO
     Some years ago Jarkko supplied patches to provide support
     for the POSIX SA_SIGINFO feature in Perl, passing the extra
     data to the Perl signal handler.

     Unfortunately, it only works with "unsafe" signals, because
     under safe signals, by the time Perl gets to run the signal
     handler, the extra information has been lost. Moreover, it's
     not easy to store it somewhere, as you can't call mutexs, or
     do anything else fancy, from inside a signal handler.

     So it strikes me that we could provide safe SA_SIGINFO

     1.  Provide global variables for two file descriptors

     2.  When the first request is made via "sigaction" for
         "SA_SIGINFO", create a pipe, store the reader in one,
         the writer in the other

     3.  In the "safe" signal handler

perl v5.12.5         Last change: 2012-11-03                   14

Perl Programmers Reference Guide                      PERLTODO(1)

         ("Perl_csighandler()"/"S_raise_signal()"), if the
         "siginfo_t" pointer non-"NULL", and the writer file
         handle is open,

         1.      serialise signal number, "struct siginfo_t" (or
                 at least the parts we care about) into a small
                 auto char buff

         2.      "write()" that (non-blocking) to the writer fd

                 1.          if it writes 100%, flag the signal
                             in a counter of "signals on the
                             pipe" akin to the current per-
                             signal-number counts

                 2.          if it writes 0%, assume the pipe is
                             full. Flag the data as lost?

                 3.          if it writes partially, croak a
                             panic, as your OS is broken.

     4.  in the regular "PERL_ASYNC_CHECK()" processing, if there
         are "signals on the pipe", read the data out,
         deserialise, build the Perl structures on the stack
         (code in "Perl_sighandler()", the "unsafe" handler), and
         call as usual.

     I think that this gets us decent "SA_SIGINFO" support,
     without the current risk of running Perl code inside the
     signal handler context. (With all the dangers of things like
     "malloc" corruption that that currently offers us)

     For more information see the thread starting with this

     Make all autovivification consistent w.r.t LVALUE/RVALUE and
     strict/no strict;

     This task is incremental - even a little bit of work on it
     will help.

  Unicode in Filenames
     chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir,
     open, opendir, qx, readdir, readlink, rename, rmdir, stat,
     symlink, sysopen, system, truncate, unlink, utime, -X.  All
     these could potentially accept Unicode filenames either as
     input or output (and in the case of system and qx Unicode in
     general, as input or output to/from the shell).  Whether a
     filesystem - an operating system pair understands Unicode in
     filenames varies.

perl v5.12.5         Last change: 2012-11-03                   15

Perl Programmers Reference Guide                      PERLTODO(1)

     Known combinations that have some level of understanding
     include Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and
     Apple UFS (in Mac OS X), NFS v4 is rumored to be Unicode,
     and of course Plan 9.  How to create Unicode filenames, what
     forms of Unicode are accepted and used (UCS-2, UTF-16,
     UTF-8), what (if any) is the normalization form used, and so
     on, varies.  Finding the right level of interfacing to Perl
     requires some thought.  Remember that an OS does not
     implicate a filesystem.

     (The Windows -C command flag "wide API support" has been at
     least temporarily retired in 5.8.1, and the -C has been
     repurposed, see perlrun.)

     Most probably the right way to do this would be this:
     "Virtualize operating system access".

  Unicode in %ENV
     Currently the %ENV entries are always byte strings.  See
     "Virtualize operating system access".

  Unicode and glob()
     Currently glob patterns and filenames returned from
     File::Glob::glob() are always byte strings.  See "Virtualize
     operating system access".

  use less 'memory'
     Investigate trade offs to switch out perl's choices on
     memory usage.  Particularly perl should be able to give
     memory back.

     This task is incremental - even a little bit of work on it
     will help.

  Re-implement ":unique" in a way that is actually thread-safe

     The old implementation made bad assumptions on several
     levels. A good 90% solution might be just to make ":unique"
     work to share the string buffer of SvPVs. That way large
     constant strings can be shared between ithreads, such as the
     configuration information in Config.

  Make tainting consistent
     Tainting would be easier to use if it didn't take documented
     shortcuts and allow taint to "leak" everywhere within an

     system() accepts a LIST syntax (and a PROGRAM LIST syntax)
     to avoid running a shell. readpipe() (the function behind
     qx//) could be similarly extended.

perl v5.12.5         Last change: 2012-11-03                   16

Perl Programmers Reference Guide                      PERLTODO(1)

  Audit the code for destruction ordering assumptions
     Change 25773 notes

         /* Need to check SvMAGICAL, as during global destruction it may be that
            AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
            is now part of the linked list of SV heads, rather than pointing to
            the original body.  */
         /* FIXME - audit the code for other bugs like this one.  */

     adding the "SvMAGICAL" check to

         if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
             MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);

     Go through the core and look for similar assumptions that
     SVs have particular types, as all bets are off during global

  Extend PerlIO and PerlIO::Scalar
     PerlIO::Scalar doesn't know how to truncate().  Implementing
     this would require extending the PerlIO vtable.

     Similarly the PerlIO vtable doesn't know about formats
     (write()), or about stat(), or chmod()/chown(), utime(), or

     (For PerlIO::Scalar it's hard to see what e.g. mode bits or
     ownership would mean.)

     PerlIO doesn't do directories or symlinks, either: mkdir(),
     rmdir(), opendir(), closedir(), seekdir(), rewinddir(),
     glob(); symlink(), readlink().

     See also "Virtualize operating system access".

  -C on the #! line
     It should be possible to make -C work correctly if found on
     the #! line, given that all perl command line options are
     strict ASCII, and -C changes only the interpretation of non-
     ASCII characters, and not for the script file handle. To
     make it work needs some investigation of the ordering of
     function calls during startup, and (by implication) a bit of
     tweaking of that order.

  Organize error messages
     Perl's diagnostics (error messages, see perldiag) could use
     reorganizing and formalizing so that each error message has
     its stable-for-all-eternity unique id, categorized by
     severity, type, and subsystem.  (The error messages would be
     listed in a datafile outside of the Perl source code, and
     the source code would only refer to the messages by the id.)
     This clean-up and regularizing should apply for all croak()

perl v5.12.5         Last change: 2012-11-03                   17

Perl Programmers Reference Guide                      PERLTODO(1)


     This would enable all sorts of things: easier
     translation/localization of the messages (though please do
     keep in mind the caveats of Locale::Maketext about too
     straightforward approaches to translation), filtering by
     severity, and instead of grepping for a particular error
     message one could look for a stable error id.  (Of course,
     changing the error messages by default would break all the
     existing software depending on some particular error

     This kind of functionality is known as message catalogs.
     Look for inspiration for example in the catgets() system,
     possibly even use it if available-- but only if available,
     all platforms will not have catgets().

     For the really pure at heart, consider extending this item
     to cover also the warning messages (see perllexwarn,

Tasks that need a knowledge of the interpreter
     These tasks would need C knowledge, and knowledge of how the
     interpreter works, or a willingness to learn.

  forbid labels with keyword names
     Currently "goto keyword" "computes" the label value:

         $ perl -e 'goto print'
         Can't find label 1 at -e line 1.

     It is controversial if the right way to avoid the confusion
     is to forbid labels with keyword names, or if it would be
     better to always treat bareword expressions after a "goto"
     as a label and never as a keyword.

  truncate() prototype
     The prototype of truncate() is currently $$. It should
     probably be "*$" instead. (This is changed in

  decapsulation of smart match argument
     Currently "$foo ~~ $object" will die with the message "Smart
     matching a non-overloaded object breaks encapsulation". It
     would be nice to allow to bypass this by using explictly the
     syntax "$foo ~~ %$object" or "$foo ~~ @$object".

  error reporting of [$a ; $b]
     Using ";" inside brackets is a syntax error, and we don't
     propose to change that by giving it any meaning. However,
     it's not reported very helpfully:

perl v5.12.5         Last change: 2012-11-03                   18

Perl Programmers Reference Guide                      PERLTODO(1)

         $ perl -e '$a = [$b; $c];'
         syntax error at -e line 1, near "$b;"
         syntax error at -e line 1, near "$c]"
         Execution of -e aborted due to compilation errors.

     It should be possible to hook into the tokeniser or the
     lexer, so that when a ";" is parsed where it is not legal as
     a statement terminator (ie inside "{}" used as a hashref,
     "[]" or "()") it issues an error something like ';' isn't
     legal inside an expression - if you need multiple statements
     use a do {...} block. See the thread starting at

  lexicals used only once
     This warns:

         $ perl -we '$pie = 42'
         Name "main::pie" used only once: possible typo at -e line 1.

     This does not:

         $ perl -we 'my $pie = 42'

     Logically all lexicals used only once should warn, if the
     user asks for warnings.  An unworked RT ticket (#5087) has
     been open for almost seven years for this discrepancy.

  UTF-8 revamp
     The handling of Unicode is unclean in many places. For
     example, the regexp engine matches in Unicode semantics
     whenever the string or the pattern is flagged as UTF-8, but
     that should not be dependent on an internal storage detail
     of the string.

  Properly Unicode safe tokeniser and pads.
     The tokeniser isn't actually very UTF-8 clean. "use utf8;"
     is a hack - variable names are stored in stashes as raw
     bytes, without the utf-8 flag set. The pad API only takes a
     "char *" pointer, so that's all bytes too. The tokeniser
     ignores the UTF-8-ness of "PL_rsfp", or any SVs returned
     from source filters.  All this could be fixed.

  state variable initialization in list context
     Currently this is illegal:

         state ($a, $b) = foo();

     In Perl 6, "state ($a) = foo();" and "(state $a) = foo();"
     have different semantics, which is tricky to implement in
     Perl 5 as currently they produce the same opcode trees. The
     Perl 6 design is firm, so it would be good to implement the
     necessary code in Perl 5. There are comments in

perl v5.12.5         Last change: 2012-11-03                   19

Perl Programmers Reference Guide                      PERLTODO(1)

     "Perl_newASSIGNOP()" that show the code paths taken by
     various assignment constructions involving state variables.

  Implement $value ~~ 0 .. $range
     It would be nice to extend the syntax of the "~~" operator
     to also understand numeric (and maybe alphanumeric) ranges.

  A does() built-in
     Like ref(), only useful. It would call the "DOES" method on
     objects; it would also tell whether something can be
     dereferenced as an array/hash/etc., or used as a regexp,

  Tied filehandles and write() don't mix
     There is no method on tied filehandles to allow them to be
     called back by formats.

  Propagate compilation hints to the debugger
     Currently a debugger started with -dE on the command-line
     doesn't see the features enabled by -E. More generally hints
     ($^H and "%^H") aren't propagated to the debugger. Probably
     it would be a good thing to propagate hints from the
     innermost non-"DB::" scope: this would make code eval'ed in
     the debugger see the features (and strictures, etc.)
     currently in scope.

  Attach/detach debugger from running program
     The old perltodo notes "With "gdb", you can attach the
     debugger to a running program if you pass the process ID. It
     would be good to do this with the Perl debugger on a running
     Perl program, although I'm not sure how it would be done."
     ssh and screen do this with named pipes in /tmp. Maybe we
     can too.

  LVALUE functions for lists
     The old perltodo notes that lvalue functions don't work for
     list or hash slices. This would be good to fix.

  regexp optimiser optional
     The regexp optimiser is not optional. It should configurable
     to be, to allow its performance to be measured, and its bugs
     to be easily demonstrated.

  "/w" regex modifier
     That flag would enable to match whole words, and also to
     interpolate arrays as alternations. With it, "/P/w" would be
     roughly equivalent to:

perl v5.12.5         Last change: 2012-11-03                   20

Perl Programmers Reference Guide                      PERLTODO(1)

         do { local $"='|'; /\b(?:P)\b/ }

     lists/perl5-porters/2007-01/msg00400.html> for the

  optional optimizer
     Make the peephole optimizer optional. Currently it performs
     two tasks as it walks the optree - genuine peephole
     optimisations, and necessary fixups of ops. It would be good
     to find an efficient way to switch out the optimisations
     whilst keeping the fixups.

  You WANT *how* many
     Currently contexts are void, scalar and list. split has a
     special mechanism in place to pass in the number of return
     values wanted. It would be useful to have a general
     mechanism for this, backwards compatible and little speed
     hit.  This would allow proposals such as short circuiting
     sort to be implemented as a module on CPAN.

  lexical aliases
     Allow lexical aliases (maybe via the syntax "my \$alias =

  entersub XS vs Perl
     At the moment pp_entersub is huge, and has code to deal with
     entering both perl and XS subroutines. Subroutine
     implementations rarely change between perl and XS at run
     time, so investigate using 2 ops to enter subs (one for XS,
     one for perl) and swap between if a sub is redefined.

     Self-ties are currently illegal because they caused too many
     segfaults. Maybe the causes of these could be tracked down
     and self-ties on all types reinstated.

  Optimize away @_
     The old perltodo notes "Look at the "reification" code in

  Virtualize operating system access
     Implement a set of "vtables" that virtualizes operating
     system access (open(), mkdir(), unlink(), readdir(),
     getenv(), etc.)  At the very least these interfaces should
     take SVs as "name" arguments instead of bare char pointers;
     probably the most flexible and extensible way would be for
     the Perl-facing interfaces to accept HVs.  The system needs
     to be per-operating-system and per-file-system
     hookable/filterable, preferably both from XS and Perl level

perl v5.12.5         Last change: 2012-11-03                   21

Perl Programmers Reference Guide                      PERLTODO(1)

     ("Files and Filesystems" in perlport is good reading at this
     point, in fact, all of perlport is.)

     This has actually already been implemented (but only for
     Win32), take a look at iperlsys.h and win32/perlhost.h.
     While all Win32 variants go through a set of "vtables" for
     operating system access, non-Win32 systems currently go
     straight for the POSIX/Unix-style system/library call.
     Similar system as for Win32 should be implemented for all
     platforms.  The existing Win32 implementation probably does
     not need to survive alongside this proposed new
     implementation, the approaches could be merged.

     What would this give us?  One often-asked-for feature this
     would enable is using Unicode for filenames, and other
     "names" like %ENV, usernames, hostnames, and so forth.  (See
     "When Unicode Does Not Happen" in perlunicode.)

     But this kind of virtualization would also allow for things
     like virtual filesystems, virtual networks, and "sandboxes"
     (though as long as dynamic loading of random object code is
     allowed, not very safe sandboxes since external code of
     course know not of Perl's vtables).  An example of a smaller
     "sandbox" is that this feature can be used to implement per-
     thread working directories: Win32 already does this.

     See also "Extend PerlIO and PerlIO::Scalar".

  Investigate PADTMP hash pessimisation
     The peephole optimiser converts constants used for hash key
     lookups to shared hash key scalars. Under ithreads,
     something is undoing this work.  See

  Store the current pad in the OP slab allocator
     Currently we leak ops in various cases of parse failure. I
     suggested that we could solve this by always using the op
     slab allocator, and walking it to free ops. Dave comments
     that as some ops are already freed during optree creation
     one would have to mark which ops are freed, and not double
     free them when walking the slab. He notes that one problem
     with this is that for some ops you have to know which pad
     was current at the time of allocation, which does change. I
     suggested storing a pointer to the current pad in the memory
     allocated for the slab, and swapping to a new slab each time
     the pad changes. Dave thinks that this would work.

  repack the optree
     Repacking the optree after execution order is determined
     could allow removal of NULL ops, and optimal ordering of OPs
     with respect to cache-line filling.  The slab allocator
     could be reused for this purpose.  I think that the best way

perl v5.12.5         Last change: 2012-11-03                   22

Perl Programmers Reference Guide                      PERLTODO(1)

     to do this is to make it an optional step just before the
     completed optree is attached to anything else, and to use
     the slab allocator unchanged, so that freeing ops is
     identical whether or not this step runs.  Note that the slab
     allocator allocates ops downwards in memory, so one would
     have to actually "allocate" the ops in reverse-execution
     order to get them contiguous in memory in execution order.


     Note that running this copy, and then freeing all the old
     location ops would cause their slabs to be freed, which
     would eliminate possible memory wastage if the previous
     suggestion is implemented, and we swap slabs more

  eliminate incorrect line numbers in warnings
     This code

         use warnings;
         my $undef;

         if ($undef == 3) {
         } elsif ($undef == 0) {

     used to produce this output:

         Use of uninitialized value in numeric eq (==) at line 4.
         Use of uninitialized value in numeric eq (==) at line 4.

     where the line of the second warning was misreported - it
     should be line 5.  Rafael fixed this - the problem arose
     because there was no nextstate OP between the execution of
     the "if" and the "elsif", hence "PL_curcop" still reports
     that the currently executing line is line 4. The solution
     was to inject a nextstate OPs for each "elsif", although it
     turned out that the nextstate OP needed to be a nulled OP,
     rather than a live nextstate OP, else other line numbers
     became misreported. (Jenga!)

     The problem is more general than "elsif" (although the
     "elsif" case is the most common and the most confusing).
     Ideally this code

         use warnings;
         my $undef;

         my $a = $undef + 1;
         my $b
           = $undef

perl v5.12.5         Last change: 2012-11-03                   23

Perl Programmers Reference Guide                      PERLTODO(1)

           + 1;

     would produce this output

         Use of uninitialized value $undef in addition (+) at line 4.
         Use of uninitialized value $undef in addition (+) at line 7.

     (rather than lines 4 and 5), but this would seem to require
     every OP to carry (at least) line number information.

     What might work is to have an optional line number in memory
     just before the BASEOP structure, with a flag bit in the op
     to say whether it's present.  Initially during compile every
     OP would carry its line number. Then add a late pass to the
     optimiser (potentially combined with "repack the optree")
     which looks at the two ops on every edge of the graph of the
     execution path. If the line number changes, flags the
     destination OP with this information.  Once all paths are
     traced, replace every op with the flag with a nextstate-
     light op (that just updates "PL_curcop"), which in turn then
     passes control on to the true op. All ops would then be
     replaced by variants that do not store the line number.
     (Which, logically, why it would work best in conjunction
     with "repack the optree", as that is already
     copying/reallocating all the OPs)

     (Although I should note that we're not certain that doing
     this for the general case is worth it)

  optimize tail-calls
     Tail-calls present an opportunity for broadly applicable
     optimization; anywhere that "return foo(...)" is called, the
     outer return can be replaced by a goto, and foo will return
     directly to the outer caller, saving (conservatively) 25% of
     perl's call&return cost, which is relatively higher than in
     C.  The scheme language is known to do this heavily.
     B::Concise provides good insight into where this
     optimization is possible, ie anywhere entersub,leavesub op-
     sequence occurs.

      perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'

     Bottom line on this is probably a new pp_tailcall function
     which combines the code in pp_entersub, pp_leavesub.  This
     should probably be done 1st in XS, and using B::Generate to
     patch the new OP into the optrees.

Big projects
     Tasks that will get your name mentioned in the description
     of the "Highlights of 5.12"

perl v5.12.5         Last change: 2012-11-03                   24

Perl Programmers Reference Guide                      PERLTODO(1)

  make ithreads more robust
     Generally make ithreads more robust. See also "iCOW"

     This task is incremental - even a little bit of work on it
     will help, and will be greatly appreciated.

     One bit would be to write the missing code in

     Fix Perl_sv_dup, et al so that threads can return objects.

     Sarathy and Arthur have a proposal for an improved Copy On
     Write which specifically will be able to COW new ithreads.
     If this can be implemented it would be a good thing.

  (?{...}) closures in regexps
     Fix (or rewrite) the implementation of the "/(?{...})/"

  A re-entrant regexp engine
     This will allow the use of a regex from inside (?{ }), (??{
     }) and (?(?{ })|) constructs.

  Add class set operations to regexp engine
     Apparently these are quite useful. Anyway, Jeffery Friedl
     wants them.

     demerphq has this on his todo list, but right at the bottom.

Tasks for microperl
     [ Each and every one of these may be obsolete, but they were
       in the old Todo.micro file]

  make creating automatic
  make creating Makefile.micro automatic
  do away with fork/exec/wait?
     (system, popen should be enough?)

  some of the really needs to be probed (using cc) in
     (uConfigure? :-) native datatype widths and endianness come
     to mind

     See attributes(5) for descriptions of the following

perl v5.12.5         Last change: 2012-11-03                   25

Perl Programmers Reference Guide                      PERLTODO(1)

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

perl v5.12.5         Last change: 2012-11-03                   26