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Daniel Spangenberg · Guest

Hello!

OK, lets write the whole stuff again, sigh!

Some days ago, Markus Werle posted as a reply to the thread
"How to use function objects to select output operator" a very usefull
class template named has_member_name, which provides a compiletime
check, whether a given type provides a name "name", referring it to
Paul Mensonides.
For those, who don't find this posting, I repeat its canonical
implementation
here (Some compilers, like gcc 3.4 need a small work-around as Markus
showed us):

template<class T>
class has_member_name
{
protected:
template<class U> static char check(typename U::name*);
template<class U> static char (& check(...))[2];

public:
enum { value = (sizeof(check<T>(0)) == 1) };
};

Belief it or not, but neither this implementation nor the proposed
workaround
(not quoted here) don't compile with VC6....
After you have stopped banging your head at your keyboard, or, depending
on
your mood, stopped laughing resoundingly, I honestly want to ask you
whether
anyone can show me an implementation, which works for VC6!!

I tried it several after hours and got one "internal compiler error"
after the other,
but in the end wasn't successful - aaaarg!

One further comment: One disadvantage of this template is, that a test
for another
"name", e.g. value_type needs another class template. Currently I only
see a
solution by introduction of two macros, like

#define DEFINE_HAS_NAME(aName)
template<class T>
class has_member_##aName
{
protected:
template<class U> static char check(typename U:: aName*);
...
}

#define HAS_NAME(aType, aName) (has_member_##aName < aType >::value)

Or did anyone find a metaprogramming technique to achieve a similar
result?

Thanks for you ideas!

Daniel from Bremen

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Markus Werle · Guest

Daniel Spangenberg wrote:

David Abrahams · Guest

Daniel Spangenberg <dsp (AT) bdal (DOT) de> writes: