[英]template template parameters and clang
I have had problems (possibly mine) with template template parameters and clang.我在模板模板参数和 clang 方面遇到了问题(可能是我的)。 The following toy example compiles and runs under g++ 4.7.0, not clang++ 3.0 (based on LLVM 3.0), both ubuntu 12.04.以下玩具示例在 g++ 4.7.0 下编译并运行,而不是在 clang++ 3.0(基于 LLVM 3.0)下,两者都是 ubuntu 12.04。
Toy example (test_1.cpp):玩具示例(test_1.cpp):
#include <iostream>
#include <memory>
struct AFn
{
void operator()()
{
; // do something
}
};
template<typename T>
struct impl
{
T *backpointer_;
};
template<typename S, template <typename> class T>
struct implT
{
T<S> *backpointer_;
};
template<typename>
class AClass;
template<>
struct implT<AFn, AClass>
{
implT(std::string message) :
message_(message)
{}
void operator()()
{
std::cout << " : " << message_ << std::endl;
}
std::string message_;
};
template<typename Fn>
class AClass
{
private:
std::shared_ptr<implT<Fn, AClass> > p_;
public:
AClass(std::string message) :
p_(std::make_shared<implT<Fn, AClass> >(message))
{}
void call_me()
{
p_->operator()();
}
};
int main(int argc, char **argv)
{
AClass<AFn> *A = new AClass<AFn>("AClass<AFn>");
A->call_me();
delete A;
return 0;
}
clang output:叮当输出:
*****@ely:~$ clang++ -std=c++11 test_1.cpp -o test_1
test_1.cpp:47:30: error: template argument for template template parameter must be a class template or
type alias template
std::shared_ptr<implT<Fn, AClass> > p_;
^
test_1.cpp:47:40: error: C++ requires a type specifier for all declarations
std::shared_ptr<implT<Fn, AClass> > p_;
^~
test_1.cpp:50:36: error: template argument for template template parameter must be a class template or
type alias template
p_(std::make_shared<implT<Fn, AClass> >(message))
^
3 errors generated.
I can't make sense of the first error. It compiles and runs fine with gcc/g++ 4.7.0. Any help would be appreciated.
As noted, it's a Clang bug.如前所述,这是一个 Clang 错误。 AClass
there is an injected-class-name , a unique grammatical construct which is both a class-name and a template-name . AClass
有一个注入类名,这是一个独特的语法结构,它既是类名又是模板名。
Another workaround is to say AClass::template AClass
.另一种解决方法是说AClass::template AClass
。 This avoids needing to qualify AClass
with its enclosing namespace.这避免了需要用其封闭的命名空间来限定AClass
。
The same thing happens for me with Clang 3.3.在 Clang 3.3 中我也发生了同样的事情。
The solution -- or workaround -- from this SO question is to replace AClass
with ::AClass
on lines 47 and 50, and then it compiles happily.解决方案——或解决方法——来自这个 SO question是在第 47 和 50 行用::AClass
替换AClass
,然后它愉快地编译。
To be honest template template parameters make my head hurt.说实话模板模板参数让我头疼。 The referenced question suggests it's a Clang bug, but I'm not enough of an expert to be able to say.引用的问题表明这是一个 Clang 错误,但我不是专家,无法说。
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