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Bug 1153295 - Add mozilla::Declval. r=nfroyd

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This commit is contained in:
Gerald Squelart 2015-04-27 18:11:00 -04:00
parent fba7e2edc1
commit 00a33b3cfd
3 changed files with 31 additions and 3 deletions
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11
mfbt/TypeTraits.h
View File

@ -811,6 +811,17 @@ struct AddRvalueReference
: detail::AddRvalueReferenceHelper<T>
{};
/* 20.2.4 Function template declval [declval] */
/**
* DeclVal simplifies the definition of expressions which occur as unevaluated
* operands. It converts T to a reference type, making it possible to use in
* decltype expressions even if T does not have a default constructor, e.g.:
* decltype(DeclVal<TWithNoDefaultConstructor>().foo())
*/
template<typename T>
typename AddRvalueReference<T>::Type DeclVal();
/* 20.9.7.3 Sign modifications [meta.trans.sign] */
template<bool B, typename T = void>

18
mfbt/tests/TestTypeTraits.cpp
View File

@ -9,6 +9,7 @@
using mozilla::AddLvalueReference;
using mozilla::AddRvalueReference;
using mozilla::DeclVal;
using mozilla::IsArray;
using mozilla::IsBaseOf;
using mozilla::IsClass;
@ -385,6 +386,23 @@ static_assert(IsSame<AddRvalueReference<void>::Type, void>::value,
static_assert(IsSame<AddRvalueReference<struct S1&>::Type, struct S1&>::value,
"not reference-collapsing struct S1& && to struct S1& correctly");
struct TestWithDefaultConstructor
{
int foo() const { return 0; }
};
struct TestWithNoDefaultConstructor
{
explicit TestWithNoDefaultConstructor(int) {}
int foo() const { return 1; }
};
static_assert(IsSame<decltype(TestWithDefaultConstructor().foo()), int>::value,
"decltype should work using a struct with a default constructor");
static_assert(IsSame<decltype(DeclVal<TestWithDefaultConstructor>().foo()), int>::value,
"decltype should work using a DeclVal'd struct with a default constructor");
static_assert(IsSame<decltype(DeclVal<TestWithNoDefaultConstructor>().foo()), int>::value,
"decltype should work using a DeclVal'd struct without a default constructor");
static_assert(IsSame<MakeSigned<const unsigned char>::Type, const signed char>::value,
"const unsigned char won't signify correctly");
static_assert(IsSame<MakeSigned<volatile unsigned short>::Type, volatile signed short>::value,

5
xpcom/glue/nsISupportsImpl.h
View File

@ -29,6 +29,7 @@
#include "mozilla/Likely.h"
#include "mozilla/MacroArgs.h"
#include "mozilla/MacroForEach.h"
#include "mozilla/TypeTraits.h"
namespace mozilla {
template <typename T>
@ -62,9 +63,7 @@ struct HasDangerousPublicDestructor
namespace mozilla {
struct IsDestructibleFallbackImpl
{
template<typename T> static T&& Declval();
template<typename T, typename = decltype(Declval<T>().~T())>
template<typename T, typename = decltype(DeclVal<T>().~T())>
static TrueType Test(int);
template<typename>