Question

There is something that has been on my mind for a long time now. Just consider this function:

template<typename T>
T foo(const T& value)
{
    return value;
}

It’s the simplest possible function wrapper for any given value. However, I’ve been wondering whether it has a “standard name” (that many would recognize, like functions such as map, filter, sqrt, etc…). And are they well-known problems that require to use such a function?

Answer 1

In principle it’s an identity function, but in practice it forces a copy of the argument.

So, if T has value semantics, it’s still a real identity.
Otherwise, it’s a cloning function.

A perfect identity would be

template<typename T>
const T& identity(const T& value)
{
    return value;
}