Re: Defining Non-Member Functions for Template Member Types
* flounder:
The compiler is unable to find a match for the call to munge() and
operator==() in is_equal() below. Can someone post an explanation and/
or suggest a workaround?
Thanks!
template<class T>
struct Foo {
struct Bar {};
};
template<class T>
bool operator==(const typename Foo<T>::Bar&, const typename
Foo<T>::Bar&);
template<class T>
void munge(typename Foo<T>::Bar* );
inline bool
is_equal(Foo<int>::Bar x, Foo<int>::Bar y)
{
munge(&x);
return x == y; // no operator "==" matches these operands
}
I googled.
See <url: http://www.codeguru.com/forum/archive/index.php/t-395268.html>;
"non-deduced context".
However while it seems the facts there are OK, the rationalization there seems
very fishy to me. Perhaps that rationalization is the standard's rationale (I'm
too lazy to check). But in a context like above I see no good reason why the
language could not have permitted the matching: there can be only one match.
I can see a bad reason, though, namely treating all types the same way, and the
above would indeed be problematic with Bar a typedef'ed name, e.g. for 'int'.
But the reason we use types and scopes (argh, declarative regions[1], now that
the C++ standardization has redefined our terminology) and so on is exactly to
discriminate between different things, even things that are technically the same
but just conceptually different, and I think the language should support that.
If the language had supported it then I think one would have had to write e.g.
template< typename T >
void munge( struct Foo<T>::Bar* );
But since the language doesn't support it the issue is moot.
Cheers & hth.,
- Alf
Notes:
[1] Or whatever the proper C++ term is!
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