Concepts in the <iterator> Header

In the <iterator> header, we’ll find concepts that can be very useful in dealing with algorithms. The functions in <iterator> do not operate directly on containers but through iterators.

std::indirect_unary_predicate<F, I>

Some concepts are related to callables. For those, we can specify that we accept only unary predicates.

A predicate is a callable that returns either a bool value or a value that can be converted to a bool. A unary predicate is a predicate that takes one parameter as its input.

The following example is just for demonstration. It will generate an error when compiled. Let’s look at the code below to get an idea of how unary predicates work.