Substitution failure is not an error: Difference between revisions

Revision as of 02:39, 17 October 2024

Latest revision as of 21:01, 29 July 2025

Line 37:

template <typename T>

struct has_typedef_foobarHasTypedefFoobar {

// Types "yes" and "no" are guaranteed to have different sizes,

// specifically sizeof(yes) == 1 and sizeof(no) == 2.

Line 55:

};

struct fooFoo {

typedef float foobar;

};

Line 61:

int main() {

std::cout << std::boolalpha;

std::cout << has_typedef_foobarHasTypedefFoobar<int>::value << std::endl; // Prints false

std::cout << has_typedef_foobarHasTypedefFoobar<fooFoo>::value << std::endl; // Prints true

return 0;

}

Line 75:

#include <iostream>

#include <type_traits>

template <typename... Ts>

using void_t = void;

template <typename T, typename = void>

struct has_typedef_foobarHasTypedefFoobar : std::false_type {};

template <typename T>

struct has_typedef_foobarHasTypedefFoobar<T, std::void_t<typename T::foobar>> : std::true_type {};

struct fooFoo {

using foobar = float;

};

Line 91 ⟶ 88:

int main() {

std::cout << std::boolalpha;

std::cout << has_typedef_foobarHasTypedefFoobar<int>::value << std::endl;

std::cout << has_typedef_foobarHasTypedefFoobar<fooFoo>::value << std::endl;

return 0;

}

Line 103 ⟶ 100:

template <typename T>

using has_typedef_foobar_tHasTypedefFoobarUnderlying = typename T::foobar;

struct fooFoo {

using foobar = float;

};

Line 111 ⟶ 108:

int main() {

std::cout << std::boolalpha;

std::cout << std::is_detected<has_typedef_foobar_tHasTypedefFoobarUnderlying, int>::value << std::endl;

std::cout << std::is_detected<has_typedef_foobar_tHasTypedefFoobarUnderlying, fooFoo>::value << std::endl;

return 0;

}