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From: patch@hpldola.HP.COM (Pat Chkoreff)
Newsgroups: comp.lang.c++
Subject: Re: default arg handling
Message-ID: <11430021@hpldola.HP.COM>
Date: 16 Mar 90 19:39:01 GMT
References: <1116@xyzzy.UUCP>
Organization: HP Elec. Design Div. -ColoSpgs
Lines: 50

/ hpldola:comp.lang.c++ / shap@delrey.sgi.com (Jonathan Shapiro) / 12:52 pm  Mar 14, 1990 /
>>In article <11430020@hpldola.HP.COM> patch@hpldola.HP.COM (Pat Chkoreff) writes:
>/ hpldola:comp.lang.c++ / shap@delrey.sgi.com (Jonathan Shapiro) /  4:13 pm  Mar 10, 1990 /
>
>> As Mark Langley has pointed out, the supplying of default arguments should
>> be thought of as the responsibility of the caller, not part of the function
>> definition.
>
> De facto, C++ says otherwise.  If what you say were true, the
> following would be legal:
>
>	extern foo(int = 5);
>
>	...
>
>	extern foo(int = 10);
>
> in the same file.  Note that C++ disallows this.
>
> Jon

According to Mark Langley's policy, the example above should NOT be legal,
because the caller's responsibility is ambiguous.  The implementation of his
policy which I proposed would in fact correctly reject the example.  Here's
why.  The compiler would generate the following:

	extern int foo(int);           // extern foo(int = 5);
	static int foo()
	{
		return foo(5);
	}

	// ...

	extern int foo(int);           // extern foo(int = 10);
	static int foo()               // This is line "10".
	{
		return foo(10);
	}

This itself is not legal, because foo() is declared twice:

	CC: "t.c", line 10: error 1034: two definitions of foo()

I still do not see a problem with either Mark Langley's policy or my
implementation of it.


Patrick Chkoreff   719-590-5983
{hpfcla,hplabs}!hpldola!patch