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[c++1z] P0490R0, NB comment GB 20: if std::tuple_size<T> is complete, use the 

tuple-like interpretation of decomposition declaration even if there is no
::value member. We already did this, anticipating this resolution, just update
comments and tweak a testcase.

llvm-svn: 289021
This commit is contained in:
Richard Smith 2016-12-08 03:24:55 +00:00
parent 41217616a8
commit 208732e954
2 changed files with 3 additions and 6 deletions
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7
clang/lib/Sema/SemaDeclCXX.cpp
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@ -983,11 +983,8 @@ static IsTupleLike isTupleLike(Sema &S, SourceLocation Loc, QualType T,
if (lookupStdTypeTraitMember(S, R, Loc, "tuple_size", Args, /*DiagID*/0))
return IsTupleLike::NotTupleLike;
// FIXME: According to the standard, we're not supposed to diagnose if any
// of the steps below fail (or if lookup for ::value is ambiguous or otherwise
// results in an error), but this is subject to a pending CWG issue / NB
// comment, which says we do diagnose if tuple_size<T> is complete but
// tuple_size<T>::value is not an ICE.
// If we get this far, we've committed to the tuple interpretation, but
// we can still fail if there actually isn't a usable ::value.
struct ICEDiagnoser : Sema::VerifyICEDiagnoser {
LookupResult &R;

2
clang/test/CXX/dcl.decl/dcl.decomp/p3.cpp
View File

@ -10,7 +10,7 @@ void no_tuple_size_1() { auto [x, y] = A(); } // ok, decompose elementwise
namespace std { template<typename T> struct tuple_size; }
void no_tuple_size_2() { auto [x, y] = A(); } // ok, decompose elementwise
struct Bad1 {};
struct Bad1 { int a, b; };
template<> struct std::tuple_size<Bad1> {};
void no_tuple_size_3() { auto [x, y] = Bad1(); } // expected-error {{cannot decompose this type; 'std::tuple_size<Bad1>::value' is not a valid integral constant expression}}