Created
September 15, 2015 17:33
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This shows how to enable a template for an explicit list of types.
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#include <iostream> | |
#include <type_traits> | |
template<typename T, typename... UsableTypes> | |
struct SearchImpl : std::is_same<T, UsableTypes>... | |
{ | |
}; | |
template<typename T, typename... UsableTypes> | |
struct Search : std::is_base_of<std::true_type, SearchImpl<T, UsableTypes...>>::type | |
{ | |
}; | |
// Enable a given template only for a given list of types. | |
// Works assuming all the types given are unique | |
template<typename T, typename... UsableTypes> | |
struct enable_for : std::enable_if<Search<T, UsableTypes...>::value, int> | |
{ | |
}; | |
// Example: | |
template<typename T, typename enable_for<T, char, short, int, long, long long>::type = 0> | |
void print_classification(T) { | |
std::cout << "This is an integral type" << std::endl; | |
} | |
template<typename T, typename enable_for<T, double, float>::type = 0> | |
void print_classification(T) { | |
std::cout << "This is a floating point type" << std::endl; | |
} | |
template<typename T, typename enable_for<T, double, float>::type = 0, | |
typename U, typename enable_for<U, char, short, int, long, long long>::type = 0> | |
void print_classification(T, U) { | |
std::cout << "float then int" << std::endl; | |
} | |
template<typename T, typename enable_for<T, char, short, int, long, long long>::type = 0, | |
typename U, typename enable_for<U, double, float>::type = 0> | |
void print_classification(T, U) { | |
std::cout << "int then float" << std::endl; | |
} | |
template<typename T, typename enable_for<T, char, short, int, long, long long>::type = 0, | |
typename U, typename enable_for<U, char, short, int, long, long long>::type = 0> | |
void print_classification(T, U) { | |
std::cout << "both int" << std::endl; | |
} | |
template<typename T, typename enable_for<T, double, float>::type = 0, | |
typename U, typename enable_for<U, double, float>::type = 0> | |
void print_classification(T, U) { | |
std::cout << "both float" << std::endl; | |
} | |
int main() { | |
std::cout << Search<int, double, int>::value << std::endl; | |
print_classification('a'); | |
print_classification((short)2); | |
print_classification(2); | |
print_classification(2l); | |
print_classification(2ll); | |
print_classification(2.); | |
print_classification(2.0f); | |
print_classification(2., 3); | |
print_classification(3, 2.); | |
print_classification(2, 2); | |
print_classification(2., 2.); | |
int a = 2; | |
int &b = a; | |
int &&c = 2; | |
print_classification(a); | |
print_classification(b); | |
print_classification(c); | |
return 0;} |
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