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cxx/include/__functional_base_03
Eric Fiselier f1626ad28d [libcxx] Rewrite C++03 __invoke. 
Summary:
This patch rewrites the C++03 `__invoke` and related meta-programming. There are a number of major changes.

`__invoke` in C++03 now has a fallback overload for when the invoke expression is ill-formed (similar to C++11). This means that the `__invoke_return` traits will return `__nat` when `__invoke(...)` is ill formed. This would previously cause a compile error.

Bullets 1-4 of `__invoke` have been rewritten. In the old version `__invoke` had 32 overloads for bullets 1 and 2,
one for each possible cv-qualified function signature with arities 0-3. 64 overloads would be needed to support member functions
with varargs. Currently these overloads were fundamentally broken. An example overload looked like:
```
template <class Rp, class Tp, class T1, class A0>
Rp __invoke(Rp (Tp::*pm)(A0) const, T1&, A0&)
```
Because `A0` appeared in two different deducible contexts it would have to deduce to be an exact match or the overload
would be rejected. This is made even worse because `A0` appears without a reference qualifier in the member function signature
and with a reference qualifier as an `__invoke` parameter. This means that only member functions that took all
of their arguments by value could be matched.

One possible fix would be to make the second occurrence of `A0` appear in a non-deducible context. This way
any type convertible to `A0` could be passed as the first parameter. The benefit of this approach is that the
signature of the member function enforces the arity and types taken by the `__invoke` signature it generates. However
nothing in the `INVOKE` specification requires this behavior.

My solution is to use a `__invoke_enable_if<PM_Type, Tp>`  metafunction to selectively enable the `__invoke` overloads for bullets 1, 2, 3 and 4.  It uses `__member_function_traits` to inspect and extract the return type and class type of the pointer to member. Using `__member_function_traits` to inspect `PM_Type` also allows us to reduce the number of `__invoke` overloads from 32 to 8 and add
varargs support at the same time.

Because `__invoke_enable_if` knows the exact return type of `__invoke` for bullets 1-4 we no longer need to use `decltype(__invoke(...))` to
compute the return type in the `__invoke_return*` traits. This will reduce the problems caused by `#define decltype(X) __typeof__(X)` in C++03.

Tests for this change have already been committed. All tests in `test/std/utilities/function.objects` now pass in C++03, previously there were 20 failures.

Reviewers: K-ballo, howard.hinnant, mclow.lists

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D11553

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@246068 91177308-0d34-0410-b5e6-96231b3b80d8
2015-08-26 20:15:02 +00:00

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// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP_FUNCTIONAL_BASE_03
#define _LIBCPP_FUNCTIONAL_BASE_03
// manual variadic expansion for <functional>
// __invoke
template <class _Ret, class _T1, bool _IsFunc, bool _IsBase>
struct __enable_invoke_imp;
template <class _Ret, class _T1>
struct __enable_invoke_imp<_Ret, _T1, true, true> {
typedef _Ret _Bullet1;
typedef _Bullet1 type;
};
template <class _Ret, class _T1>
struct __enable_invoke_imp<_Ret, _T1, true, false> {
typedef _Ret _Bullet2;
typedef _Bullet2 type;
};
template <class _Ret, class _T1>
struct __enable_invoke_imp<_Ret, _T1, false, true> {
typedef typename add_lvalue_reference<
typename __apply_cv<_T1, _Ret>::type
>::type _Bullet3;
typedef _Bullet3 type;
};
template <class _Ret, class _T1>
struct __enable_invoke_imp<_Ret, _T1, false, false> {
typedef typename add_lvalue_reference<
typename __apply_cv<decltype(*_VSTD::declval<_T1>()), _Ret>::type
>::type _Bullet4;
typedef _Bullet4 type;
};
template <class _Ret, class _T1>
struct __enable_invoke_imp<_Ret, _T1*, false, false> {
typedef typename add_lvalue_reference<
typename __apply_cv<_T1, _Ret>::type
>::type _Bullet4;
typedef _Bullet4 type;
};
template <class _Fn, class _T1,
class _Traits = __member_pointer_traits<_Fn>,
class _Ret = typename _Traits::_ReturnType,
class _Class = typename _Traits::_ClassType>
struct __enable_invoke : __enable_invoke_imp<
_Ret, _T1,
is_member_function_pointer<_Fn>::value,
is_base_of<_Class, typename remove_reference<_T1>::type>::value>
{
};
__nat __invoke(__any, ...);
// first bullet
template <class _Fn, class _T1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet1
__invoke(_Fn __f, _T1& __t1) {
return (__t1.*__f)();
}
template <class _Fn, class _T1, class _A0>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet1
__invoke(_Fn __f, _T1& __t1, _A0& __a0) {
return (__t1.*__f)(__a0);
}
template <class _Fn, class _T1, class _A0, class _A1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet1
__invoke(_Fn __f, _T1& __t1, _A0& __a0, _A1& __a1) {
return (__t1.*__f)(__a0, __a1);
}
template <class _Fn, class _T1, class _A0, class _A1, class _A2>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet1
__invoke(_Fn __f, _T1& __t1, _A0& __a0, _A1& __a1, _A2& __a2) {
return (__t1.*__f)(__a0, __a1, __a2);
}
template <class _Fn, class _T1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet2
__invoke(_Fn __f, _T1& __t1) {
return ((*__t1).*__f)();
}
template <class _Fn, class _T1, class _A0>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet2
__invoke(_Fn __f, _T1& __t1, _A0& __a0) {
return ((*__t1).*__f)(__a0);
}
template <class _Fn, class _T1, class _A0, class _A1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet2
__invoke(_Fn __f, _T1& __t1, _A0& __a0, _A1& __a1) {
return ((*__t1).*__f)(__a0, __a1);
}
template <class _Fn, class _T1, class _A0, class _A1, class _A2>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet2
__invoke(_Fn __f, _T1& __t1, _A0& __a0, _A1& __a1, _A2& __a2) {
return ((*__t1).*__f)(__a0, __a1, __a2);
}
template <class _Fn, class _T1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet3
__invoke(_Fn __f, _T1& __t1) {
return __t1.*__f;
}
template <class _Fn, class _T1>
inline _LIBCPP_INLINE_VISIBILITY
typename __enable_invoke<_Fn, _T1>::_Bullet4
__invoke(_Fn __f, _T1& __t1) {
return (*__t1).*__f;
}
// fifth bullet
template <class _Fp>
inline _LIBCPP_INLINE_VISIBILITY
decltype(_VSTD::declval<_Fp&>()())
__invoke(_Fp& __f)
{
return __f();
}
template <class _Fp, class _A0>
inline _LIBCPP_INLINE_VISIBILITY
decltype(_VSTD::declval<_Fp&>()(_VSTD::declval<_A0&>()))
__invoke(_Fp& __f, _A0& __a0)
{
return __f(__a0);
}
template <class _Fp, class _A0, class _A1>
inline _LIBCPP_INLINE_VISIBILITY
decltype(_VSTD::declval<_Fp&>()(_VSTD::declval<_A0&>(), _VSTD::declval<_A1&>()))
__invoke(_Fp& __f, _A0& __a0, _A1& __a1)
{
return __f(__a0, __a1);
}
template <class _Fp, class _A0, class _A1, class _A2>
inline _LIBCPP_INLINE_VISIBILITY
decltype(_VSTD::declval<_Fp&>()(_VSTD::declval<_A0&>(), _VSTD::declval<_A1&>(), _VSTD::declval<_A2&>()))
__invoke(_Fp& __f, _A0& __a0, _A1& __a1, _A2& __a2)
{
return __f(__a0, __a1, __a2);
}
template <class _Fp, bool = __has_result_type<__weak_result_type<_Fp> >::value>
struct __invoke_return
{
typedef typename __weak_result_type<_Fp>::result_type type;
};
template <class _Fp>
struct __invoke_return<_Fp, false>
{
typedef decltype(__invoke(_VSTD::declval<_Fp&>())) type;
};
template <class _Tp, class _A0>
struct __invoke_return0
{
typedef decltype(__invoke(_VSTD::declval<_Tp&>(), _VSTD::declval<_A0&>())) type;
};
template <class _Rp, class _Tp, class _A0>
struct __invoke_return0<_Rp _Tp::*, _A0>
{
typedef typename __enable_invoke<_Rp _Tp::*, _A0>::type type;
};
template <class _Tp, class _A0, class _A1>
struct __invoke_return1
{
typedef decltype(__invoke(_VSTD::declval<_Tp&>(), _VSTD::declval<_A0&>(),
_VSTD::declval<_A1&>())) type;
};
template <class _Rp, class _Class, class _A0, class _A1>
struct __invoke_return1<_Rp _Class::*, _A0, _A1> {
typedef typename __enable_invoke<_Rp _Class::*, _A0>::type type;
};
template <class _Tp, class _A0, class _A1, class _A2>
struct __invoke_return2
{
typedef decltype(__invoke(_VSTD::declval<_Tp&>(), _VSTD::declval<_A0&>(),
_VSTD::declval<_A1&>(),
_VSTD::declval<_A2&>())) type;
};
template <class _Ret, class _Class, class _A0, class _A1, class _A2>
struct __invoke_return2<_Ret _Class::*, _A0, _A1, _A2> {
typedef typename __enable_invoke<_Ret _Class::*, _A0>::type type;
};
#endif // _LIBCPP_FUNCTIONAL_BASE_03
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