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To: Alan Mackenzie <acm@muc.de>
Cc: gcc@gcc.gnu.org
Subject: Re: Help requested on C++ template syntax (for Emacs development).
References: <20080610183707.GB4844@muc.de> <m3zlptglv9.fsf@google.com>
From: Ian Lance Taylor <iant@google.com>
Date: Tue, 10 Jun 2008 19:05:00 -0000
In-Reply-To: <m3zlptglv9.fsf@google.com> (Ian Lance Taylor's message of "Tue\, 10 Jun 2008 11\:56\:10 -0700")
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Ian Lance Taylor <iant@google.com> writes:

> Alan Mackenzie <acm@muc.de> writes:
>
>> I'm thinking of things like
>>
>>     foo (a < b, c > d);
>>
>> I think this is unambiguously a function call with 2 parameters, the
>> expressions "a < b" and "c > d".  It cannot be be one with 1 parameter
>> beginning with the template invocation "a < b , c >".  Or can it?
>
> No, it can't be, because a<b, c> is a type.  The result would be
> foo(TYPE d), which can not be a function call.  On the other hand, if
> there were a type before foo then this would be a function
> declaration.  For example, this is valid C++ code:
>
> template <int a1, int a2> class a;
>
> int fn(int d, int e)
> {
>   const int b = 1;
>   const int c = 2;
>   typedef int f;
>   f foo (int, int);
>   f foo (a < b, c > d);
>   foo (e < b, c > d);
> }
>
> The line "f foo (a < b, c > d);" uses a template, the line "foo (e <
> b, c > d);" does not.

Oh, wait, I forgot about constructors.  This is valid C++ code:

template <int a1, int a2> class a;

const int b = 1;
const int c = 2;
int d;
int e;

class foo
{
  foo (a < b, c > d);
};

extern void quux (int, int);

void bar()
{
  quux (e < b, c > d);
}

Inside the class foo, you've got a template, inside the function bar,
you've got a function call.

I think you're going to have a hard time with this.

Ian