Template metaprogramming: Difference between revisions

Revision as of 20:09, 8 June 2021

Revision as of 15:44, 18 June 2021

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What exactly "programming at compile-time" means can be illustrated with an example of a factorial function, which in non-template C++ can be written using recursion as follows:

<syntaxhighlight lang=cpp>

unsigned int factorial(unsigned int n) {

return n == 0 ? 1 : n * factorial(n - 1);

}

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By using template metaprogramming and template specialization to provide the ending condition for the recursion, the factorials used in the program—ignoring any factorial not used—can be calculated at compile time by this code:

<syntaxhighlight lang=cpp>

template <unsigned int nN>

struct factorial {

enumstatic {constexpr unsigned value = nN * factorial<nN - 1>::value };

};

template <>

struct factorial<0> {

enumstatic {constexpr unsigned value = 1 };

};