On Fri, 22 Nov 2002 13:48:01 +0200, "Peter Dimov" <[EMAIL PROTECTED]>
wrote:
>From: "David Abrahams" <[EMAIL PROTECTED]>
>>
>> Here's what I think might be a correct implementation:
>>
>> template <class T, class U> T implicit_cast(U const& x) { return x; }
>> template <class T, class U> T implicit_cast(U& x) { return x; }
>
>The correct implementation IIRC is
>
>template<class T> T implicit_cast(typename identity<T>::type x) { return
>x; }
I do know we all hate macros but this could be taken into
consideration if we want something usable in constant expressions too.
The idea is to use a static_cast after checking that the conversion
could have also been done implicitly:
template <typename T>
struct identity { typedef T type;};
template <typename T>
T implicit_cast (typename identity<T>::type x) {
return x;
}
template <typename T, std::size_t sz >
struct check_helper{
typedef T type;
};
#define IMPLICIT_CAST(dst_type, expr) \
( static_cast< check_helper<dst_type, \
sizeof(implicit_cast<dst_type>(expr)) > \
:: type>(expr) )
Thoughts?
Genny.
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