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perlmroapi (1)


perlmroapi - Perl method resolution plugin interface


Please see following description for synopsis


Perl Programmers Reference Guide                    PERLMROAPI(1)

     perlmroapi - Perl method resolution plugin interface

     As of Perl 5.10.1 there is a new interface for plugging and
     using method resolution orders other than the default
     (linear depth first search).  The C3 method resolution order
     added in 5.10.0 has been re-implemented as a plugin, without
     changing its Perl-space interface.

     Each plugin should register itself with "Perl_mro_register"
     by providing the following structure

         struct mro_alg {
             AV *(*resolve)(pTHX_ HV *stash, U32 level);
             const char *name;
             U16 length;
             U16 kflags;
             U32 hash;

         Pointer to the linearisation function, described below.

         Name of the MRO, either in ISO-8859-1 or UTF-8.

         Length of the name.

         If the name is given in UTF-8, set this to "HVhek_UTF8".
         The value is passed direct as the parameter kflags to

         A precomputed hash value for the MRO's name, or 0.

     The "resolve" function is called to generate a linearised
     ISA for the given stash, using this MRO. It is called with a
     pointer to the stash, and a level of 0. The core always sets
     level to 0 when it calls your function - the parameter is
     provided to allow your implementation to track depth if it
     needs to recurse.

     The function should return a reference to an array
     containing the parent classes in order. The caller is
     responsible for incrementing the reference count if it wants
     to keep the structure. Hence if you have created a temporary
     value that you keep no pointer to, "sv_2mortal()" to ensure
     that it is disposed of correctly. If you have cached your

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Perl Programmers Reference Guide                    PERLMROAPI(1)

     return value, then return a pointer to it without changing
     the reference count.

     Computing MROs can be expensive. The implementation provides
     a cache, in which you can store a single "SV *", or anything
     that can be cast to "SV *", such as "AV *". To read your
     private value, use the macro "MRO_GET_PRIVATE_DATA()",
     passing it the "mro_meta" structure from the stash, and a
     pointer to your "mro_alg" structure:

         meta = HvMROMETA(stash);
         private_sv = MRO_GET_PRIVATE_DATA(meta, &my_mro_alg);

     To set your private value, call

         Perl_mro_set_private_data(aTHX_ meta, &c3_alg, private_sv);

     The private data cache will take ownership of a reference to
     private_sv, much the same way that "hv_store()" takes
     ownership of a reference to the value that you pass it.

     For examples of MRO implementations, see
     "S_mro_get_linear_isa_c3()" and the "BOOT:" section of
     mro/mro.xs, and "S_mro_get_linear_isa_dfs()" in mro.c

     The implementation of the C3 MRO and switchable MROs within
     the perl core was written by Brandon L Black. Nicholas Clark
     created the pluggable interface, refactored Brandon's
     implementation to work with it, and wrote this document.

     See attributes(5) for descriptions of the following

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

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Perl Programmers Reference Guide                    PERLMROAPI(1)

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

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