> -----Original Message-----
> From: David B. Held [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, December 05, 2002 10:56 AM
> To: [EMAIL PROTECTED]
> Subject: [boost] Re: [MPL] Making Generators
>
>
> "David Abrahams" <[EMAIL PROTECTED]> wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > [...]
> > I don't know... well, it could detect whether there was a ::type
> > member, [...]
>
> Really??? Is it possible to detect the presence of a typedef
> without generating an error? How do you do this? I think
> this is a very useful feature!
>
> Dave
Vandevoorde and Josuttis call it SFINAE, "substitution failute is not an
error."
In "C++ Templates: The Complete Guide" (Recommended), they give this
example on pages 106-107:
typedef char RT1;
typedef struct {char a[2];} RT2;
template<typename T> RT1 test(typename T::X const*);
template<typename T> RT2 test(...);
#define type_has_member_type_X(T) \
(sizeof(test<T>(0) == 1)
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