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Fix std::visit for the zero variants case.

Browse Source 
Summary:
The following code is broken:

```
    std::visit([]{});
```

Reviewers: EricWF

Reviewed By: EricWF

Differential Revision: https://reviews.llvm.org/D33090

llvm-svn: 302773
This commit is contained in:
Michael Park 2017-05-11 07:17:12 +00:00
parent c59ced36aa
commit 215f55f526
2 changed files with 17 additions and 16 deletions
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23
libcxx/include/variant
View File

@ -425,30 +425,21 @@ struct __base {
constexpr auto __fmatrix =
__make_fmatrix<_Visitor&&,
decltype(_VSTD::forward<_Vs>(__vs).__as_base())...>();
const size_t __indices[] = {__vs.index()...};
return __at(__fmatrix, __indices)(_VSTD::forward<_Visitor>(__visitor),
_VSTD::forward<_Vs>(__vs).__as_base()...);
return __at(__fmatrix, __vs.index()...)(
_VSTD::forward<_Visitor>(__visitor),
_VSTD::forward<_Vs>(__vs).__as_base()...);
}
private:
template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
static constexpr const _Tp& __at_impl(const _Tp& __elem, const size_t*) {
return __elem;
}
static constexpr const _Tp& __at(const _Tp& __elem) { return __elem; }
template <class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY
static constexpr auto&& __at_impl(const array<_Tp, _Np>& __elems,
const size_t* __index) {
return __at_impl(__elems[*__index], __index + 1);
}
template <class _Tp, size_t _Np, size_t _Ip>
template <class _Tp, size_t _Np, typename... _Indices>
inline _LIBCPP_INLINE_VISIBILITY
static constexpr auto&& __at(const array<_Tp, _Np>& __elems,
const size_t (&__indices)[_Ip]) {
return __at_impl(__elems, begin(__indices));
size_t __index, _Indices... __indices) {
return __at(__elems[__index], __indices...);
}
template <class _Fp, class... _Fs>

10
libcxx/test/std/utilities/variant/variant.visit/visit.pass.cpp
View File

@ -94,6 +94,16 @@ void test_call_operator_forwarding() {
using Fn = ForwardingCallObject;
Fn obj{};
const Fn &cobj = obj;
{ // test call operator forwarding - no variant
std::visit(obj);
assert(Fn::check_call<>(CT_NonConst | CT_LValue));
std::visit(cobj);
assert(Fn::check_call<>(CT_Const | CT_LValue));
std::visit(std::move(obj));
assert(Fn::check_call<>(CT_NonConst | CT_RValue));
std::visit(std::move(cobj));
assert(Fn::check_call<>(CT_Const | CT_RValue));
}
{ // test call operator forwarding - single variant, single arg
using V = std::variant<int>;
V v(42);