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C++: Template Conditional Structures

Bjarne-stroustrup
 

This page lists the conditional structures offered by different programming languages. Common conditional structures are if-then-else and switch.

Template metaprogramming

Selecting a type depending on a compile time condition

template<bool Condition, typename ThenType, typename Elsetype> struct ifthenelse;

template<typename ThenType, typename ElseType> struct ifthenelse<true, ThenType, ElseType>
{
	typedef ThenType type;
};

template<typename ThenType, typename ElseType> struct ifthenelse<false, ThenType, ElseType>
{
	typedef ElseType type;
};

// example usage: select type based on size
ifthenelse<INT_MAX == 32767, // 16 bit int?
long int,         // in that case, we'll need a long int
int>              // otherwise an int will do
::type myvar;              // define variable myvar with that type

SOURCE

Content is available under GNU Free Documentation License 1.2.