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What Are Blocks?

3:59 with Jason Seifer

At its most basic, a block is statements of code that are grouped together. The statements can be grouped inside of curly braces or between the do and end keywords.

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Blocks and Return Values

Blocks must use the implicit return format in Ruby.

A Note on Convention

Conventionally, most Ruby programmers distinguish between the two formats the following way:

Multi line blocks are usually written using the do and end format.
- Single line blocks are usually written using curly braces {}.

Code Samples

A code block using the do and end syntax:

3.times do
  puts "Hello world!"
  puts "This is the second line."
  true
end

A code block using curly braces:

3.times { puts "Hello world!" }

[MUSIC] 0:00

[SOUND] You may have seen a block before in Ruby code, they're really common. 0:04

At its most basic, a block is a statement of code that is grouped together. 0:09

The statements can be grouped inside of curly braces, or 0:15

between the do and end keywords. 0:18

Blocks are actually a piece of syntax in Ruby and 0:21

not explicitly an object like everything else. 0:24

Blocks can be a little confusing at first, but they're actually really easy. 0:28

Let's take a look at some blocks now using workspaces. 0:32

Okay, so I have launched a new Ruby workspace. 0:36

Or, you can click on the launch workspace button on the side. 0:40

Now let's go ahead and create a file that we're going to call block_examples.rb. 0:44

And we can go ahead and close the welcome document. 0:52

Now let's go ahead and write a simple block. 0:57

We're just gonna do a quick loop, and print Hello world to the screen. 1:01

And then close it by writing end. 1:08

Now we go through and everything in between do and end is part of the block. 1:11

Let's go ahead and run it, and just make sure it works. 1:20

Now you'll notice there's no conditional to exit the block. 1:23

So we're going to have to exit it using Ctrl+C. 1:26

So as we can see, it keep s printing hello world to the screen. 1:29

And we can see after hitting Ctrl+C that this interrupts the loop. 1:35

Now we can also write the loop using curly braces. 1:39

And I'm gonna clear my screen here and 1:46

if we run this again we should see the same thing. 1:48

And we do. 1:53

Now it may take a moment once you hit Ctrl+C for it to stop and that's okay. 1:54

That's perfectly normal. 1:59

It might be your Internet catching up with workspaces. 2:00

So, here we go. Now, let's go ahead and 2:04

change this block a little bit so we don't have to do Ctrl+C every single time. 2:06

We'll change this to printing it out three times. 2:13

Now, with block syntax it doesn't really matter if you use do and end, or 2:19

the curly braces. 2:24

There are some nuances, with the precedents of those. 2:25

The curly braces have higher precedence. 2:30

But we don't really need to worry about that right now. 2:33

Now when we have these blocks, choosing between curly braces, and do and 2:36

end is usually a matter of convention. 2:41

Most Rubyists when writing a block, if the block only 2:45

takes up a single line, like this one does, we will use curly braces. 2:50

The other convention is, if it takes up multiple lines, 2:55

to put that inside of a do end block. 3:00

And that's not done for any functionality reasons. 3:07

It is done for visual separation, and it just kind of looks a little bit better, 3:11

potentially depending on your preferences, if multiline blocks are within do and end. 3:15

Now here's something interesting about blocks. 3:20

You can't use the return statement inside. 3:23

So, here's an example, if we run this, 3:30

this is going to error out, saying there's an unexpected return. 3:32

So, you can't use the return statement inside of blocks. 3:38

If you are going to return something from a block, it needs to use an implicit 3:42

return, which would just be the return value of the last line of the block. 3:47

So if we run that again, 3:54

we can see it doesn't error out with that local jump error this time. 3:55

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