Use Lambdas as Predicates with the Algorithm Library

Some functions in the algorithm library require the use of a predicate function. A predicate is a function (or functor or lambda) that tests a condition and returns a Boolean true/false response.

How to do it

For this recipe, we will experiment with the count_if() algorithm using different types of predicates:

• First, let’s create a function for use as a predicate. A predicate takes a certain number of arguments and returns a bool. A predicate for count_if() takes one argument: