Lambda expressions

A lambda is essentially an anonymous function as a literal expression:

auto la = []{ return "Hello\n"; };

The variable la may now be used as if it were a function:

cout << la();

It can be passed to another function:

f(la);

It can be passed to another lambda:

const auto la = []{ return "Hello\n"; };
const auto lb = [](auto a){ return a(); };
cout << lb(la);

Output:

Hello

Or it can be passed anonymously (as a literal):

const auto lb = [](auto a){ return a(); };
cout << lb([]{ return "Hello\n"; });

Closures

The term closure is often applied to any anonymous function. Strictly speaking, a closure is a function that allows the use of symbols outside its own lexical scope.

You may have noticed the square brackets in the definition of a lambda:

auto la = []{ return "Hello\n"; };

The square brackets are used to specify a list of captures. Captures are outside variables...