可以在 CRTP 方法中对派生 类 使用约束吗?
Can you use constraints on derived classes in CRTP methods?
像这样的有效 C++20 代码吗?
#include <iostream>
template <typename T>
concept impls_decrement = requires(T it) { it.decrement(); };
template <class Derived>
struct iterator_facade {
Derived& operator--()
requires impls_decrement<Derived>
{
auto& self = static_cast<Derived&>(*this);
self.decrement();
return self;
}
};
struct my_iterator : iterator_facade<my_iterator> {
void decrement() {
std::cout << "decrement" << std::endl;
}
};
int main() {
my_iterator iter;
--iter;
return 0;
}
改编自 vector-of-bool 博客 post。
使用最新版本的 gcc,代码有效 fine, but the latest version of clang gives this error:
prog.cc:25:4: error: cannot decrement value of type 'my_iterator'
--iter;
^ ~~~~
1 error generated.
哪个编译器是正确的?
正如 Barry 所提到的,代码是有效的,这是 Clang bug 44833。
与此同时,我通过编写如下代码 (demo) 解决了这个问题:
#include <iostream>
template <typename T>
concept impls_decrement = requires(T it) { it.decrement(); };
template <class Derived>
struct iterator_facade {
template <class T=Derived>
requires impls_decrement<T>
Derived& operator--()
{
auto& self = static_cast<Derived&>(*this);
self.decrement();
return self;
}
};
struct my_iterator : iterator_facade<my_iterator> {
void decrement() {
std::cout << "decrement" << std::endl;
}
};
int main() {
my_iterator iter;
--iter;
return 0;
}
像这样的有效 C++20 代码吗?
#include <iostream>
template <typename T>
concept impls_decrement = requires(T it) { it.decrement(); };
template <class Derived>
struct iterator_facade {
Derived& operator--()
requires impls_decrement<Derived>
{
auto& self = static_cast<Derived&>(*this);
self.decrement();
return self;
}
};
struct my_iterator : iterator_facade<my_iterator> {
void decrement() {
std::cout << "decrement" << std::endl;
}
};
int main() {
my_iterator iter;
--iter;
return 0;
}
改编自 vector-of-bool 博客 post。
使用最新版本的 gcc,代码有效 fine, but the latest version of clang gives this error:
prog.cc:25:4: error: cannot decrement value of type 'my_iterator'
--iter;
^ ~~~~
1 error generated.
哪个编译器是正确的?
正如 Barry 所提到的,代码是有效的,这是 Clang bug 44833。
与此同时,我通过编写如下代码 (demo) 解决了这个问题:
#include <iostream>
template <typename T>
concept impls_decrement = requires(T it) { it.decrement(); };
template <class Derived>
struct iterator_facade {
template <class T=Derived>
requires impls_decrement<T>
Derived& operator--()
{
auto& self = static_cast<Derived&>(*this);
self.decrement();
return self;
}
};
struct my_iterator : iterator_facade<my_iterator> {
void decrement() {
std::cout << "decrement" << std::endl;
}
};
int main() {
my_iterator iter;
--iter;
return 0;
}