Question

typename_function ::=        // 没有包含在附录A中
    $typename(expression)
  | $typename(data_type)

语法 23-2 — typename函数语法（没有包含在附录A中）

$typename系统函数返回一个代表其自变量的解析类型的字符串。

The return string is constructed in the following steps:

1. A typedef that creates an equivalent type is resolved back to built-in or user defined types.
2. The default signing is removed, even if present explicitly in the source
3. System generated names are created for anonymous structs, unions and enums.
4. A ‘$’ is used as the placeholder for the name of an anonymous unpacked array.
5. Actual encoded values are appended with numeration named constants.
6. User defined type names are prefixed with their defining package or scope namespace.
7. Array ranges are represented as unsized decimal numbers.
8. Whitespace in the source is removed and a single space is added to separate identifiers and keywords from each other.

This process is similar to the way that type equality is computed, except that array ranges and built-in equivalent types are not normalized in the generated string. Thus $typename can be used in string comparisons for stricter type-checking of arrays than $typeof.

When called with an expression as its argument, $typename returns a string that represents the self-determined type result of the expression. The expression's return type is determined during elaboration but never evaluated. When used as an elaboration time constant, the expression shall not contain any hierarchical identifiers or references to elements of dynamic objects.

// source code // $typename would return
typedef bit node; // "bit"
node signed [2:0] X; // "bit signed[2:0]"
int signed Y; // "int"

package A;
    enum {A,B,C=99} X; // "enum{A=32’d0,B=32’d1,C=’32bX}A::e$1"
    typedef bit [9:1’b1] word // "A::bit[9:1]"
endpackage : A

import A:.*;

module top;
    typedef struct {node A,B;} AB_t;
    AB_t AB[10]; // "struct{bit A;bit B;}top.AB_t$[0:9]"
    ...
endmodule