------- Comment #2 from jwakely dot gcc at gmail dot com 2008-03-08 15:25
-------
(In reply to comment #0)
> // 1
> #include <functional>
>
> typedef int value_type;
>
> // void argument type
> template class std::unary_function<void, value_type>;
eurgh, even more of an abomination than int f(void) :-)
> template class std::pointer_to_unary_function<void, value_type>;
This fails, correctly I think. It's analogous to this illegal declaration:
typedef void T;
int f(T);
> // void return type
> template class std::unary_function<value_type, void>;
> template class std::pointer_to_unary_function<value_type, void>;
These are OK, aren't they?
> And more specific things:
>
> // 2
> #include <functional>
> void foo() { };
>
> // pointer_to_unary_function
> void test01()
> {
> typedef std::pointer_to_unary_function<void, void> pfunc;
> pfunc p(&foo);
this is invalid, foo is not a unary function so the number of parameters
doesn't match. The declaration void f(void) is valid for C compatibility, but
that doesn't make it a unary function.
14.8.2para2 says type deduction can fail due to "Attempting to create a
function type in which a parameter has a type of void." That's discussing a
different situation, but the principle is the same. I couldn't find anything
more specific.
> // 3
> #include <functional>
> // unary_function
> struct void_unary : public std::unary_function<void, void>
> {
> typedef std::unary_function<void, void> base_type;
> typedef base_type::Arg argument_type;
> typedef base_type::Result result_type;
> };
Hmm, I suppose this is legal, although ill-advised.
> Is this usage standards-conforming?
I think the declarations and typedefs are legal, but using them isn't
necessarily possible. So you can't assign &foo to a unary_function, and you
couldn't define this member:
Result void_unary::f(Arg);
Thankfully the void f(void) syntax is not valid in templates, because there's
no need for C compatibility in template code.
I don't think this is a bug.
--
jwakely dot gcc at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jwakely dot gcc at gmail dot
| |com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33628
