Precedence

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

There are several operators in the table that we have not yet discussed; these will be covered in subsequent chapters:

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 rightmost 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 Chapter 1, Introduction. 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 Chapter 1, Introduction. A special kind of associative array called an aggregation is described in Chapter 9, Aggregations. The [] operator can also be used to index into fixed-size C arrays as well, as described in Chapter 5, Pointers and Arrays.