Concepts are not yet here, but there are solutions.

Detection Idiom - A Stopgap for Concepts

by Simon Brand

From the article:

Concepts is a proposed C++ feature which allows succinct, expressive, and powerful constraining of templates. They have been threatening to get in to C++ for a long time now, with the first proposal being rejected for C++11. They were finally merged in to C++20 a few months ago, which means we need to hold on for another few years before they’re in the official standard rather than a Technical Specification. In the mean time, there have been various attempts to implement parts of concepts as a library so that we can have access to some of the power of Concepts without waiting for the new standard. The detection idiom – designed by Walter Brown and part of the Library Fundamentals 2 Technical Specification – is one such solution. This post will outline the utility of it, and show the techniques which underlie its implementation.