模板类的模板化构造函数的显式实例化 [英] Explicit instantiation of templated constructor for template class
问题描述
我不确定是否是Clang 3.2中的错误或违反C ++ 03,但是对于模板类的模板化构造函数的显式实例化失败了,但模板类的模板成员函数的显式实例化成功。 / p>
例如,下面的编译没有clang ++和g ++的问题:
template< typename T>
class Foo
{
public:
template< typename S>
void Bar(const Foo< S& foo)
{}
};
template class Foo< int> ;;
template class Foo< float> ;;
template void Foo< int> :: Bar(const Foo< int>& foo);
template void Foo< int> :: Bar(const Foo< float>& foo);
template void Foo< float> :: Bar(const Foo< int>& foo);
template void Foo< float> :: Bar(const Foo< float>& foo);
,但是下面的编译没有使用g ++的警告,但是clang ++失败:
模板< typename T>
class Foo
{
public:
template< typename S>
Foo(const Foo< S& foo)
{}
};
template class Foo< int> ;;
template class Foo< float> ;;
template Foo< int> :: Foo(const Foo< int>& foo);
template Foo< int> :: Foo(const Foo< float>& foo);
template Foo< float> :: Foo(const Foo< int>& foo);
template Foo< float> :: Foo(const Foo< float>& foo);
特别是,我看到两个错误消息:
TemplateMember.cpp:12:20:error:explicit instantiation是指成员
函数'Foo< int> :: Foo' b $ b template Foo< int> :: Foo(const Foo< int>& foo);
^
TemplateMember.cpp:9:16:note:显式实例化在这里
模板类Foo< int> ;;
^
这是违反标准还是clang ++中的错误?
看起来您发现了一个GCC错误。这两个名称都是隐含声明的复制构造函数:
template Foo template Foo< float> :: Foo(const Foo< float>& foo);
每个[temp.explicit] p4,
< blockquote>
如果显式实例化的声明命名一个隐含声明的特殊成员函数(第12条),程序就会生成错误。
因此,Clang拒绝此代码是正确的。
I am uncertain if it is a bug in Clang 3.2 or a violation of C++03, but it appears that explicit instantiation of templated constructors for template classes fails, but explicit instantiation of templated member functions of template classes succeeds.
For instance, the following compiles without a problem with both clang++ and g++:
template<typename T>
class Foo
{
public:
template<typename S>
void Bar( const Foo<S>& foo )
{ }
};
template class Foo<int>;
template class Foo<float>;
template void Foo<int>::Bar( const Foo<int>& foo );
template void Foo<int>::Bar( const Foo<float>& foo );
template void Foo<float>::Bar( const Foo<int>& foo );
template void Foo<float>::Bar( const Foo<float>& foo );
whereas the following compiles without warning with g++ but fails with clang++:
template<typename T>
class Foo
{
public:
template<typename S>
Foo( const Foo<S>& foo )
{ }
};
template class Foo<int>;
template class Foo<float>;
template Foo<int>::Foo( const Foo<int>& foo );
template Foo<int>::Foo( const Foo<float>& foo );
template Foo<float>::Foo( const Foo<int>& foo );
template Foo<float>::Foo( const Foo<float>& foo );
In particular, I see two error messages of the form:
TemplateMember.cpp:12:20: error: explicit instantiation refers to member
function 'Foo<int>::Foo' that is not an instantiation
template Foo<int>::Foo( const Foo<int>& foo );
^
TemplateMember.cpp:9:16: note: explicit instantiation refers here
template class Foo<int>;
^
Is this a violation of the standard or a bug in clang++?
It looks like you've found a GCC bug. These both name the implicitly-declared copy constructor:
template Foo<int>::Foo( const Foo<int>& foo );
template Foo<float>::Foo( const Foo<float>& foo );
Per [temp.explicit]p4,
If the declaration of the explicit instantiation names an implicitly-declared special member function (Clause 12), the program is ill-formed.
Therefore Clang is correct to reject this code.
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