Default function that just returns the passed value?

Question

As a lazy developer, I like to use this trick to specify a default function:

template 

        

Answer 1

This is called the identity function. Unfortunately, it is not part of the C++ standard, but you can easily build one yourself.

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If you happen to use g++, you can activate its extensions with -std=gnu++11 and then

#include 
#include 

template  >
void index(std::array &x, Function&& f = Function())
{
    for (unsigned int i = 0; i < Size; ++i) {
        x[i] = f(i);
    }
}

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Maybe it will be available in C++20, see std::identity. Until then you may look at boost's version at boost::compute::identity.