It would be nice to have an identity function object

[mclow]

From the -users ML:

I use the following function on a regular basis:

template < class P_T > P_T const &same (P_T const &p) { return p; }

I use it for two purposes:

1. to pass an identity function to an API that expects a unary function,
2. to help the compiler identify the right chain of type conversions.

The standard uses static_cast for (2), which could be used but it disables
some compile-time verification so I would rather not use static_cast when
not absolutely necessary.

[dabrahams]

Whether this is really an algorithm, and how it should be written in the presence of rvalue references, are both open questions.