Mantis 1566-macros

P1800-2008/D4

Add variable number arguments to text macros

The proposal is based on Mantis 1571

In Section 21.5.1

CHANGE

Change the syntax in Syntax 21-2 from (FROM MANTIS 1571)

list_of_formal_arguments ::=
    formal_argument { , formal_argument }
formal_argument ::=
    simple_identifier [ = default_text ]

TO

list_of_formal_arguments ::=
formal_argument { , formal_argument } [ , last_format_argument ]
formal_argument ::=
    simple_identifier [ = default_text ]
last_format_argument ::=
simple_identifier ... [ = default_text ]

CHANGE (TEXT FROM MANTIS 1571)

If formal arguments are used, the list of formal argument names shall be enclosed in parentheses following

the name of the macro. The formal argument names shall be simple_identifiers, separated by commas and

optionally whitespace. The left parenthesis shall follow the text macro name immediately, with no space in between.

A formal macro argument may have a default. A default is specified by appending an = token after the formal argument name, followed by the default text. The default text is substituted for the formal argument if no corresponding actual argument is specified.

The default text may be explicitly specified to be empty by adding an = token after the formal argument name, followed by a comma (or a right parenthesis if it is the last argument in the argument list.)

TO

If formal arguments are used, the list of formal argument names shall be enclosed in parentheses following

the name of the macro. The formal argument names shall be simple_identifiers, separated by commas and

optionally whitespace. The left parenthesis shall follow the text macro name immediately, with no space in between.

A formal macro argument may have a default. A default is specified by appending an = token after the formal argument name, followed by the default text. The default text is substituted for the formal argument if no corresponding actual argument is specified.

The default text may be explicitly specified to be empty by adding an = token after the formal argument name, followed by a comma (or a right parenthesis if it is the last argument in the argument list.)

The last argument in the list of formal argument names may be followed by an ellipsis (...) and is then called a multiple argument. In that case, a list of actual arguments, separated by commas, may be specified in the argument list in the text macro call. The list of actual arguments, including the commas, shall be subsituted for the formal multiple argument in the macro text. A default may be specified for a formal multiple argument as well, after the ellipsis. Such a default may itself be a multiple argument list.

Within the scope of the macro text, the predefined macro `__ARGC__ designates the number of arguments specified in the multiple argument list (or of the default if the default was used). A particular member of the multiple argument list may be specified by appending a simple non-negative integer constant index within square brackets to the multiple argument list name. The arguments in the multiple argument list are numbered from 0 to `__ARGC__ -1 . It shall be an error to specify a number beyond the end of the list.

CHANGE

It shall be an error to specify more actual arguments than the number of formal arguments. (FROM Mantis 1571)

TO

It shall be an error to specify more actual arguments than the number of formal arguments unless the last formal argument is a multiple argument.

CHANGE (TEXT FROM Mantis 1571)

Example without defaults:

...

Example with defaults:

...

TO (ADD NEW EXAMPLES AFTER OTHER EXAMPLES)

Example without defaults:

...

`define MUTEX(name, V...) name: assert($onehot0{V})

`MUTEX (one_driver, a,b,c);

// expands to "one_driver: assert($onehot0{a,b,c});

`define HEAD(Q...) Q[0]

`HEAD(3,1,4,15) // evaluates to 3

Example with defaults:

`define MUTEX(name, V...=a,b) name: assert($onehot0{V})

`MUTEX (one_driver);

// expands to "one_driver: assert($onehot0{a,b});