C++20 concepts: part 2

In the first article about concepts, the basic rationale behind C++20’s concept was explained with the help of a very simple generic print method. Specifically the problem with pre-C++20 generic code not enforcing a requirements on the interface it should provide on the template type parameter T eventually causing a messy compilation error during substitution of T with the actual type.

In this article, I intend to dive deeper into C++20 concepts and explain more details on the idea behind concepts and usage.

Note that I’ll stick to examples with function templates for the time being and start explaining class templates in the later issues of the article after all foundations related to concepts have been explained.

1. Concepts as semantic constraint on template type

According to C++ reference page:

The intent of concepts is to model semantic categories (Number, Range, Regular Function) rather than syntactic restrictions … The ability to specify meaningful semantics is a defining characteristic of a true concept, as opposed to a syntactic constraint.

This simply means that C++ concepts model the semantic restrictions on the template parameters in terms of the interface they provide and not care how the (substituted) template parameters are used.