Function objects and lambda expressions
Lambda expressions, introduced in C++11, and further enhanced with every C++ version since, are one of the most useful features in modern C++. Their versatility comes not only from easily passing functions to algorithms, but also their use in a lot of circumstances where you need to pass the code around, especially as you can store a lambda in a std::function.
Although lambdas made these programming techniques vastly simpler to work with, everything mentioned in this section is possible to perform without them. A lambda—or, more formally, a lambda expression—is a convenient way of constructing a function object. But instead of using lambda expressions, we could instead implement classes with operator() overloaded, and then instantiate these to create function objects.
We will explore the lambda's similarities to these kinds of classes later, but first I will introduce lambda expressions in a simple use case.
