Template specialization
In the last post I define a recursive template function to calculate factorial. But since only the first 21 factorials fit in an unsigned 64-bit int I can just define them all with specialization.
// all overflow calculations return zero
template< int N > factorial( ) { return 0; /* overflow */ }
// brute force
template<> factorial< 0 >( ) { return 1; }
template<> factorial< 1 >( ) { return 1; }
template<> factorial< 2 >( ) { return 2; }
template<> factorial< 3 >( ) { return 3*2; }
template<> factorial< 4 >( ) { return 4*3*2; }
.. etc ..
template<> factorial< 20 >( )
{
return 20ull *
19 * 18 * 17 * 16 * 15 * 14 * 13 * 12 * 11 *
10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1;
}
Factorial is probably the wrong example to use here, but this could be useful in other situations, such as defining specialized functions for all the values of an enum.
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