Re: c++/9298: [3.4 regression] [new parser] ICE with function-pointer-typetemplate args

[Wolfgang Bangerth <bangerth at ticam dot utexas dot edu>]

> sorry for the confusion, I was *quite* wrong.

No problem :-) You're hereby sentenced to three days in the C++ testcase 
diction jail:
  struct bars {
    bool behind ();
  };
  ...
  if (bars().behind())
    printf("foo :-)");


> Let's have another look at the code:
> 
> The declaration of foo as a static template function is of course legal.
> But I disagree with you when you say
> 
> > It's illegal, though, to use its address as a template parameter!
> 
> Why should it be illegal? You can use the address of a static variable as
> a template parameter, too:
> 
> ------------snip here-------------
> int i;
> template <int*> void foo() {}
> template void foo<&i> ();
> ----------------------------------

Values for pointer- or reference-type template arguments need to have 
_external_ linkage. "int i" does have that, "static void foo()" doesn't.


> Given that, the following code should compile IMHO (the EDG front-end
> thinks so, too):
> 
> ----------------------snip here-------------------
> struct A
> {
>     typedef void (*pfun)();
> 
>     template <pfun> static void bar() {}
> };
> 
> template <int> static void foo() {}
> 
> template void A::bar< &foo<0> >();
> ----------------------snip here-------------------
> 
> Alas, each gcc version since 2.95.x rejects the code with a message similar to
> 
> bug.cc:10: `&foo<0>' is not a valid template argument
> bug.cc:10: template-id `bar<(&foo<0>)>' for `void A::bar()' does not match any 
>    template declaration

EDG is wrong (surprisingly), and gcc is right: foo has internal linkage, 
and its address is therefore not a valid one for a template parameter.
Once you remove the static from the declaration of foo, it compiles 
cleanly.

It's just too bad that here the error message is not really good:

GCC2.96:
tmp/g> gcc -c x.cc
x.cc:10: `&foo<0>' is not a valid template argument
x.cc:10: template-id `bar<(&foo<0>)>' for `A::bar ()' does not match
any template declaration

PRESENT CVS:
tmp/g> ../build-gcc/gcc-install/bin/gcc -c x.cc
x.cc:10: error: template-id `bar<(&foo<0>)>' for `void A::bar()' does not match
   any template declaration


It's particularly bad since gcc-CVS knows about this. If I take your 
example from above, and make it invalid by adding "static" to the 
declaration of "int i", then I get:

x.cc:3: error: address of non-extern `i' cannot be used as template argument
x.cc:3: error: template-id `foo<(&i)>' for `void foo()' does not match any
   template declaration


Regards
  Wolfgang

-------------------------------------------------------------------------
Wolfgang Bangerth             email:            bangerth@ticam.utexas.edu
                              www: http://www.ticam.utexas.edu/~bangerth/