Precedence DTrace Rules
The D rules for operator precedence and associativity are described in the following table. These rules are somewhat complex, but are necessary to provide precise compatibility with the ANSI-C operator precedence rules. The table entries are in order from highest precedence to lowest precedence.
Table 2-11 D Operator Precedence and Associativity
| Operators | Associativity |
|---|---|
|
|
left to right |
|
|
right to left |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
left to right |
|
|
right to left |
|
|
right to left |
|
|
left to right |
The following operators are discussed in subsequent sections:
-
sizeof– Computes the size of an object -
offsetof– Computes the offset of a type member -
stringof– Converts the operand to a string -
xlate– Translates a data type -
unary &– Computes the address of an object -
unary *– Dereferences a pointer to an object -
-> and .– Accesses a member of a structure or union type
The comma (,) operator listed in the table is for compatibility with the ANSI-C comma operator, which can be used to evaluate a set of expressions in left-to-right order and return the value of the right most expression. This operator is provided strictly for compatibility with C and should generally not be used.
The () entry in the table of operator precedence represents a function call; examples of calls to functions such as printf() and trace() are presented in Output Formatting in DTrace. A comma is also used in D to list arguments to functions and to form lists of associative array keys. This comma is not the same as the comma operator and does not guarantee left-to-right evaluation. The D compiler provides no guarantee as to the order of evaluation of arguments to a function or keys to an associative array. You should be careful of using expressions with interacting side-effects, such as the pair of expressions i and i++, in these contexts.
The []entry in the table of operator precedence represents an array or associative array reference. Examples of associative arrays are presented in Associative Arrays. A special kind of associative array called an aggregation is described in DTrace Aggregations. The [] operator can also be used to index into fixed-size C arrays as well, as described in Pointers and Arrays in DTrace.