Re: Forward declaring standard library classes

[Theodore Papadopoulo <Theodore dot Papadopoulo at sophia dot inria dot fr>]

Are you allowing yourself to modify slightly (with no user visible 
change, but the ABI should be checked...) the classes vector, list, etc...

If yes, what you can do is:

Create or better reuse two types (true_type, false_type). If I 
remember correctly those already exist. Alternatinvely, you might use 
static const bool private members.

In each container add a :
typedef {true_type,false_type} swappable;
preferably as private and a friend declaration for your _UseSwap.
Also, you would have to forward declare _UseSwap or include it.

Then define you _UseSwap as:

template<typename _Tp>
struct _UseSwap {
    {enum{_M_type = SOMETHING(_Tp::swappable)};};	
};

The SOMETHING is either accessing some field of true_type, false_type 
(eg a static const member) or involving some template specialized to 
give the proper value :

template <typename> struct _One_For_True { };
template <> struct _One_For_True<true_type> { {enum{_M_type = 1}; };
template <> struct _One_For_True<false_type> { {enum{_M_type = 0}; };


Alternatinvely, you might use static const bool private members (so 
no need for types, you directly define:
static const bool swappable = {true,false};
The friend stuff remains the same.

template<typename _Tp>
struct _UseSwap {
     {enum{_M_type = _Tp::swappable ? 1 : 0; };};

	Theo.

--------------------------------------------------------------------
Theodore Papadopoulo
Email: Theodore.Papadopoulo@sophia.inria.fr Tel: (33) 04 92 38 76 01
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