C++ 使用来自 CRTP 模板-模板基类的构造函数

Question

从 curiously recursing template pattern (CRTP) 继承构造函数的语法是什么？模板模板基类？

template<typename T, template<typename> typename U>
struct Base {
    Base(int) { }
};

template<typename T>
struct Derived : public Base<T, Derived> {
    using Base<T, Derived>::Base;
};

int main(int argc, char *argv[]) {
    Derived<double> foo(4);
    return 0;
}

在VS2019中，上述代码会导致如下错误:

error C3210: 'Base<double, Derived<double> >': a member using-declaration can only be applied to a base class member
error C3881: can only inherit constructor from direct base

使上述代码工作所需的语法是什么？

Answer 1

这是有效的代码，它 does compile with GCC 9.2 .尝试更新版本的编译器或不同的编译器。或联系您的实现者。

在那之前，这里有一个解决方法 does compile with MSVC现在:

template<typename T, template<typename> typename U>
struct Base {
    Base(int) { }
};

template<typename T>
struct Derived;

template<typename T>
using Base_type = Base<T, Derived>;

template<typename T>
struct Derived : public Base_type<T> {
    using Base_type<T>::Base;
};

int main() {
    Derived<double> foo(4);
    return 0;
}