英文:
C++: How to write a concept that demands that constructor is noexcept?
问题
如何编写一个要求类具有noexcept构造函数的概念？例如，在Clang 15.0.7中，以下static_assert是成立的，尽管我觉得它不应该成立。
class Ragdoll {
int age_ = -1;
public:
Ragdoll(int age) /* noexcept */ : age_(age) {}
int meow() const;
int lose_hair();
};
template<typename Cat>
concept cat = requires(Cat cat) {
noexcept(Cat{42});
{ cat.meow() } -> std::same_as<int>;
};
static_assert(cat<Ragdoll>);
那么在概念中，noexcept表达式究竟是在做什么呢？（也可以链接一些好的概念教程）
英文:
How do I write a concept that demands that the class has a noexcept constructor? For example, the following static_assert is true in Clang 15.0.7, although I feel that it shouldn't.
class Ragdoll {
int age_ = -1;
public:
Ragdoll(int age) /* noexcept */ : age_(age) {}
int meow() const;
int lose_hair();
};
template<typename Cat>
concept cat = requires(Cat cat) {
noexcept(Cat{42});
{ cat.meow() } -> std::same_as<int>;
};
static_assert(cat<Ragdoll>);
What is the noexcept expression doing then anyway in the concept? (Feel free to also link any good concepts tutorials)
答案1
得分: 5
以下是翻译好的部分：
template<typename Cat>
concept cat = requires(const Cat cat) {
{ Cat{42} } noexcept;
// 如果你想要成员函数也是 noexcept 的话，可以这样写
{ cat.meow() } noexcept -> std::same_as<int>;
};
英文:
You can check if an expression is noexcept in a requires expression with a noexcept before the -> or ;:
template<typename Cat>
concept cat = requires(const Cat cat) {
{ Cat{42} } noexcept;
// If you wanted the member function to be noexcept too for example
{ cat.meow() } noexcept -> std::same_as<int>;
};
答案2
得分: 2
这似乎有效（在触发static_assert的意义上），尽管我更愿意以某种方式在requires子句中指定它。
英文:
Okay, apparently the following works (in the sense that it triggers the static_assert), although I'd prefer to somehow specify it in the requires clause.
template<typename Cat>
concept cat = noexcept(Cat{42}) && requires(Cat cat) {
{ cat.meow() } -> std::same_as<int>;
};
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