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(uplifting music)

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-: Welcome to this bonus section for the course.

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In this section, we'll learn the basics

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of C++ plus Lambda expressions.

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Lambda expressions were first introduced in C++ 11,

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and then extended in C++ 14 and 17.

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They provide a very convenient way

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to provide functionality exactly where it's needed

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without writing lots and lots of code.

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In order to understand Lambda expressions,

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it's important to understand what they are

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and what motivated their addition to C++.

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First, we'll look

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at what motivated C++ Lambda expressions,

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and in order to do that, we'll quickly review using C++

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function objects, or functors.

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You may remember that I spoke

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about functors in the Algorithms lecture

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in the Standard Template Library section of the course.

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Why is it important to understand function objects?

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Well, because behind the scenes

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the C++ compiler generates anonymous

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or unnamed functional objects from Lambda expressions.

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Then we'll look at the syntax

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of a Lambda expression and go through every part of it.

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We'll then see the difference

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between stateless and stateful Lambda expressions.

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Stateless lambdas only know

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about the information that's passed into them

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via the parameter list, pretty much like a regular function.

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We'll then learn about stateful lambdas.

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These are a bit more complex

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since they can capture the elements

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from the environment that they execute in,

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so they close around their environment,

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and that's where the concept of a closure comes from.

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This is a very, very powerful concept

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and happens via the Lambda's capture list.

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There are lots of options here,

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and we'll look at the ones that are most commonly used.

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Finally, we'll look at Lambdas in the context of the STL.

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We've already seen basic lambdas in the STL section,

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but we'll look at a few more examples here.

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That's it.

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I hope you enjoyed this section.

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Please remember, I'm only covering the basics

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of C++ Lambda expressions.

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They can get very complex when we use them

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with templates, as class functions,

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and when we pass and return Lambda's to and from functions.

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So let's see what motivated C++ Lambda expressions

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in the next video.