Re: [boost] [type_traits] request for decayed<T>::type

From: John Maddock (john_at_[hidden])
Date: 2005-01-02 11:01:08

>> Any thoughts from the type_traits authors?
>
> I think decayed is an excellent trait.  Your implementation should be 
> modified to also take care of functions converting into function pointers 
> though.  It's a shame about the const qaulifier in your example make_pair 
> messing up the int[10] conversion to int*.

I agree that it should work for function to function-pointer conversions as 
well.

I've attached a slightly improved version that gets your non-const make_pair 
working, also uses remove_bounds rather than the range lib traits (just to 
keep things in the type_traits family).

Not sure about the "decayed" name, but I can't think of anything better 
right now.

> This is a characteristic of pair, not make_pair.  And it could be disabled 
> by restricting the member template constructor in:
>
> template <class T1, class T2>
> struct pair {
>   typedef T1 first_type;
>   typedef T2 second_type;
>
>   T1 first;
>   T2 second;
>   pair();
>   pair(const T1& x, const T2& y);
>   template<class U, class V> pair(const pair<U, V> &p);
> };
>
> such that is_convertible<U, T1> and is_convertible<V, T2>, which is a 
> change I would support.

If we do that, then we should do the same for the tuple constructors as 
well.

John.