C++
Type Traits
Type relations with std::is_same
Example
C++11
The std::is_same<T, T> type relation is used to compare two types. It will evaluate as boolean, true if the types are the same and false if otherwise.
e.g.
// Prints true on most x86 and x86_64 compilers.
std::cout << std::is_same<int, int32_t>::value << "\n";
// Prints false on all compilers.
std::cout << std::is_same<float, int>::value << "\n";
// Prints false on all compilers.
std::cout << std::is_same<unsigned int, int>::value << "\n";
The std::is_same type relation will also work regardless of typedefs. This is actually demonstrated in the first example when comparing int == int32_t however this is not entirely clear.
e.g.
// Prints true on all compilers.
typedef int MyType
std::cout << std::is_same<int, MyType>::value << "\n";
Using std::is_same to warn when improperly using a templated class or function.
When combined with a static assert the std::is_same template can be valuable tool in enforcing proper usage of templated classes and functions.
e.g. A function that only allows input from an int and a choice of two structs.
#include <type_traits>
struct foo {
int member;
// Other variables
};
struct bar {
char member;
};
template<typename T>
int AddStructMember(T var1, int var2) {
// If type T != foo || T != bar then show error message.
static_assert(std::is_same<T, foo>::value ||
std::is_same<T, bar>::value,
"This function does not support the specified type.");
return var1.member + var2;
}
