Constraining Variable Templates and Template Aliases

As we know, apart from function templates and class templates, we also have variable templates and alias templates in C++. These make no exception of the need to define constraints. The same rules for constraining the template arguments discussed so far apply to these two. In this lesson, we’ll demonstrate them shortly. Let’s start with variable templates.

Constraining variable templates

It’s a typical example to define the PI constant for showing how variable templates work. Indeed, it’s a simple definition that looks as follows: