C ++编译时检查模板类型中是否存在方法 [英] C++ compile time check if method exists in template type
问题描述
我有一个调用成员函数的模板.如何使用 static_assert
检查该方法是否存在?
I have a template that calls a member function. How do I check with static_assert
that the method exists?
struct A {
};
struct B {
int foo() { return 42; } };
template <typename T> struct D {
static_assert(/* T has foo */, "T needs foo for reasons");
int bar() {
return t.foo();
}
T t; };
int main() {
D<A> d;
std::cout << d.bar() << std::endl;
return 0; }
我知道这只会产生A没有foo的编译器错误,但是我想使用 static_assert
检查并提供更好的错误输出.
I know this will just generate a compiler error that A does not have foo but I would like to check and give a better error output using static_assert
.
推荐答案
由于您使用的是 static_assert
,所以我断言您至少在使用C ++ 11.这样可以编写如下内容:
Since you use static_assert
I assert that you are using at least C++11. This allows to write something like this:
#include <type_traits>
template<class ...Ts>
struct voider{
using type = void;
};
template<class T, class = void>
struct has_foo : std::false_type{};
template<class T>
struct has_foo<T, typename voider<decltype(std::declval<T>().foo())>::type> : std::true_type{};
并且您只使用静态字段 value
( has_foo< your_type> :: value
)-如果为true,则您的类型具有函数 foo
And you just use static field value
(has_foo<your_type>::value
) - if it's true then your type has function foo
.
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