Date: Sun Sep 17 2006 - 04:53:28 PDT
This is a draft proposal for Mantis 1571, to add default values for macro arguments. The obvious advantage of default values for macro arguments is not having to specify them, making their usage shorter and more readable. A second advantage is being able to change the default by a single change instead of having to change the argument value in every usage of the macro. Syntax change: Change the syntax in Syntax 19-2 in 1364-2005 from list_of_formal_arguments ::= formal_argument_identifier { , formal_argument_identifier } formal_argument_identifier ::= simple_identifier to list_of_formal_arguments ::= formal_argument { , formal_argument } formal_argument ::= simple_identifier [ = default_value ] (Note that the default value does not have to be an expression syntactically. This is noted in Mantis 1333.) Add the following text: A formal macro argument may have a default value. If a default value is not explicitly specified, then the macro argument is considered to have a null default value. The default value is substituted for the formal argument if no corresponding actual argument is specified. If fewer actual arguments are specified than the number of formal arguments, then the default values are substituted for the additional formal arguments. It shall be an error to specify more actual arguments than the number of formal arguments in the macro. Examples: `define MACRO(a=5,b="B",c) $display( a ,, b ,, c ) ; // c has no explicit default, implicit null default `MACRO ( , 2, 3 ) // argument a omitted `MACRO ( 1 , , 3 ) // argument b omitted `MACRO ( , 2, ) // arguments a and c omitted `MACRO ( 1 ) // arguments b and c omitted `MACRO () // all three arguments omitted Shalom Shalom Bresticker Intel Jerusalem LAD DA +972 2 589-6852 +972 54 721-1033 I don't represent Intel
