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Merged
StephanTLavavej merged 3 commits into from
Oct 3, 2020
Merged

Pre-decay template arguments to _Front_binder #1293

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3bbe023
Pre-decay template arguments to _Front_binder
CaseyCarter Sep 15, 2020
659d213
Review comments
CaseyCarter Sep 17, 2020
4b8521b
Update stl/inc/functional
StephanTLavavej Sep 17, 2020
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33 changes: 18 additions & 15 deletions stl/inc/functional
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Original file line number Diff line number Diff line change
Expand Up @@ -1557,24 +1557,18 @@ constexpr auto _Call_front_binder(index_sequence<_Ix...>, _Cv_FD&& _Obj, _Cv_tup
template <class _Fx, class... _Types>
class _Front_binder { // wrap bound callable object and arguments
private:
static_assert(is_constructible_v<decay_t<_Fx>, _Fx>,
"std::bind_front() requires the decayed callable to be constructible from an undecayed callable");
static_assert(is_move_constructible_v<decay_t<_Fx>>,
"std::bind_front() requires the decayed callable to be move constructible");
static_assert(conjunction_v<is_constructible<decay_t<_Types>, _Types>...>,
"std::bind_front() requires the decayed bound arguments to be constructible from undecayed bound arguments");
static_assert(conjunction_v<is_move_constructible<decay_t<_Types>>...>,
"std::bind_front() requires the decayed bound arguments to be move constructible");
using _Seq = index_sequence_for<_Types...>;

using _Seq = index_sequence_for<_Types...>;
using _First = decay_t<_Fx>;
using _Second = tuple<decay_t<_Types>...>;
_Compressed_pair<_Fx, tuple<_Types...>> _Mypair;

_Compressed_pair<_First, _Second> _Mypair;
_STL_INTERNAL_STATIC_ASSERT(is_same_v<_Fx, decay_t<_Fx>>);
_STL_INTERNAL_STATIC_ASSERT((is_same_v<_Types, decay_t<_Types>> && ...));

public:
constexpr explicit _Front_binder(_Fx&& _Func, _Types&&... _Args)
: _Mypair(_One_then_variadic_args_t{}, _STD forward<_Fx>(_Func), _STD forward<_Types>(_Args)...) {}
template <class _FxInit, class... _TypesInit,
enable_if_t<sizeof...(_TypesInit) != 0 || !is_same_v<remove_cvref_t<_FxInit>, _Front_binder>, int> = 0>
constexpr explicit _Front_binder(_FxInit&& _Func, _TypesInit&&... _Args)
: _Mypair(_One_then_variadic_args_t{}, _STD forward<_FxInit>(_Func), _STD forward<_TypesInit>(_Args)...) {}

template <class... _Unbound>
constexpr auto operator()(_Unbound&&... _Unbargs) & noexcept(noexcept(
Expand Down Expand Up @@ -1614,7 +1608,16 @@ public:
// FUNCTION TEMPLATE bind_front
template <class _Fx, class... _Types>
_NODISCARD constexpr auto bind_front(_Fx&& _Func, _Types&&... _Args) {
return _Front_binder<_Fx, _Types...>(_STD forward<_Fx>(_Func), _STD forward<_Types>(_Args)...);
static_assert(is_constructible_v<decay_t<_Fx>, _Fx>,
"std::bind_front requires the decayed callable to be constructible from an undecayed callable");
static_assert(is_move_constructible_v<decay_t<_Fx>>,
"std::bind_front requires the decayed callable to be move constructible");
static_assert(conjunction_v<is_constructible<decay_t<_Types>, _Types>...>,
"std::bind_front requires the decayed bound arguments to be constructible from undecayed bound arguments");
static_assert(conjunction_v<is_move_constructible<decay_t<_Types>>...>,
"std::bind_front requires the decayed bound arguments to be move constructible");

return _Front_binder<decay_t<_Fx>, decay_t<_Types>...>(_STD forward<_Fx>(_Func), _STD forward<_Types>(_Args)...);
}
#endif // _HAS_CXX20

Expand Down
61 changes: 61 additions & 0 deletions tests/std/tests/P0356R5_bind_front/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -164,4 +164,65 @@ int main() {
auto bound7 = move(bound6);
assert(*move(bound6)() == -9000);
assert(*move(bound7)() == 1234);

// Also test GH-1292 "bind_front violates [func.require]p8" in which the return type of bind_front inadvertently
// depends on the value category and/or cv-qualification of its arguments.
{
struct S {
int i = 42;
};
S s;
auto lambda = [](S x) { return x.i; };
auto returns_lambda = [=] { return lambda; };
auto returns_const_lambda = [=]() -> const decltype(lambda) { return lambda; };
auto returns_const_S = []() -> const S { return {}; };

using T = decltype(bind_front(lambda, s));
static_assert(is_same_v<decltype(bind_front(lambda, move(s))), T>);
static_assert(is_same_v<decltype(bind_front(lambda, S{})), T>);

static_assert(is_same_v<decltype(bind_front(move(lambda), s)), T>);
static_assert(is_same_v<decltype(bind_front(move(lambda), move(s))), T>);
static_assert(is_same_v<decltype(bind_front(move(lambda), S{})), T>);

static_assert(is_same_v<decltype(bind_front(returns_lambda(), s)), T>);
static_assert(is_same_v<decltype(bind_front(returns_lambda(), move(s))), T>);
static_assert(is_same_v<decltype(bind_front(returns_lambda(), S{})), T>);

static_assert(is_same_v<decltype(bind_front(lambda, as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(lambda, move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(lambda, returns_const_S())), T>);

static_assert(is_same_v<decltype(bind_front(move(lambda), as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(move(lambda), move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(move(lambda), returns_const_S())), T>);

static_assert(is_same_v<decltype(bind_front(returns_lambda(), as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(returns_lambda(), move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(returns_lambda(), returns_const_S())), T>);

static_assert(is_same_v<decltype(bind_front(as_const(lambda), s)), T>);
static_assert(is_same_v<decltype(bind_front(as_const(lambda), move(s))), T>);
static_assert(is_same_v<decltype(bind_front(as_const(lambda), S{})), T>);

static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), s)), T>);
static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), move(s))), T>);
static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), S{})), T>);

static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), s)), T>);
static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), move(s))), T>);
static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), S{})), T>);

static_assert(is_same_v<decltype(bind_front(as_const(lambda), as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(as_const(lambda), move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(as_const(lambda), returns_const_S())), T>);

static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(move(as_const(lambda)), returns_const_S())), T>);

static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), as_const(s))), T>);
static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), move(as_const(s)))), T>);
static_assert(is_same_v<decltype(bind_front(returns_const_lambda(), returns_const_S())), T>);
}
}