std::conditional

```
std::conditional
C++ Utilities library Type support
Defined in header <type_traits>
template< bool B, class T, class F >
struct conditional;
(since C++11)
```

=====================
```
#include <iostream>
#include <type_traits>
#include <typeinfo>

int main()
{
typedef std::conditional<true, int, double>::type Type1;
typedef std::conditional<false, int, double>::type Type2;
typedef std::conditional<sizeof(int) >= sizeof(double), int, double>::type Type3;

std::cout << typeid(Type1).name() << '\n';
std::cout << typeid(Type2).name() << '\n';
std::cout << typeid(Type3).name() << '\n';
}
```

Possible output:
```
int
double
double
```