1
00:00:06,540 --> 00:00:08,730
- Hello, again, and
welcome to lesson nine.

2
00:00:08,730 --> 00:00:10,980
This lesson continues
the theme of functions,

3
00:00:10,980 --> 00:00:14,370
and shows how to define
nested functions and closures.

4
00:00:14,370 --> 00:00:16,140
Nested functions are
quite straightforward,

5
00:00:16,140 --> 00:00:17,760
so we'll cover them first.

6
00:00:17,760 --> 00:00:20,520
Then we'll spend the rest of
the lesson looking at closures,

7
00:00:20,520 --> 00:00:23,430
which are similar to
Lambdas in other languages.

8
00:00:23,430 --> 00:00:26,250
We'll have a look at the
syntax of simple closures first

9
00:00:26,250 --> 00:00:29,580
using full closure syntax
so you understand the idea.

10
00:00:29,580 --> 00:00:31,830
Then we'll see how you
can use tight inference

11
00:00:31,830 --> 00:00:33,303
to simplify the syntax.

12
00:00:34,530 --> 00:00:38,130
Closures are called closures
because they can capture

13
00:00:38,130 --> 00:00:41,700
or enclose variables
defined in external scope.

14
00:00:41,700 --> 00:00:43,980
We'll see how to capture
variables by reference,

15
00:00:43,980 --> 00:00:47,610
first of all, which is borrowing, invest.

16
00:00:47,610 --> 00:00:50,100
Then we'll see how to
capture variables by value

17
00:00:50,100 --> 00:00:53,820
so that the closure claims
ownership of the variable.

18
00:00:53,820 --> 00:00:56,520
We wrap up the lesson with
a look at how to iterate

19
00:00:56,520 --> 00:00:59,850
over collection and perform
an operation on each element,

20
00:00:59,850 --> 00:01:01,320
which is quite a good example

21
00:01:01,320 --> 00:01:04,083
of why to use closures in practice.