Why having concepts?

Concepts Lite vs enable_if

by Andrzej Krzemieński

From the article:

This post contains quite advanced material. I assume you are already familiar with Concepts Lite. For an overview of what Concepts Lite is, I recommend this proposal. Also, I have found this blog very useful regarding the details of and issues with concepts’ mechanics. One could look at Concepts Lite as three features:

1. A superior alternative to enable_if (or overload hiding).
2. The subsumption relation that enables the additional control of partial ordering in the overload resolution process.
3. A convenient tool for building compile-time predicates that check for valid types and expressions.

In this post I will only focus on the first feature, and try to answer the question, “what do we need Concepts Lite for, given that we already have std::enable_if (and SFINAE)?”