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Calling Blocks

5:37 with Jason Seifer

Ruby gives us different ways to call blocks. In this video, we'll explore the yield keyword and using block.call.

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This is an example of calling the block using the call method:

def get_name(prompt, &block)
  print prompt
  name = gets.chomp
  block.call(name)
  name
end

my_name = get_name do |your_name|
  puts "That's a cool name, #{your_name}!"
end

puts "my_name: #{my_name}"

The block_given? keyword can be used to conditionally call a block if one was passed to a method:

def get_name(prompt, &block)
  print prompt
  name = gets.chomp
  block.call(name) if block_given?
  name
end

my_name = get_name("Name: ") do |your_name|
  puts "That's a cool name, #{your_name}!"
end

puts "my_name: #{my_name}"

Ruby gives us several ways to work with blocks when we write our methods. 0:01

During your career as a Ruby programmer, 0:05

you'll encounter different ways methods are written using blocks. 0:07

Let's take a look at some of the ways blocks can be written now 0:12

using WorkSpaces. 0:15

Okay, so let's take a look at a couple different ways of calling blocks. 0:17

Now what I'm going to do is open up this block_argument.rb file 0:21

that we just used and I'm gonna copy it and then create a new file. 0:27

We'll call it calling_blocks.rb and 0:33

I'm just gonna paste everything from the block arguments file into there. 0:38

Okay, so here is our get_name method. 0:43

So let's say we wanted to turn this into a more typical method and 0:48

send an argument where we want to print the prompt that we send it. 0:54

So we'll say print prompt and then a colon a space. 1:01

Now when we call it we can say enter your name and then let's go ahead and run it, 1:11

just make sure it works. 1:15

Okay, so that works just like we expect. 1:20

Now you'll notice we send in the argument to the method just like we would 1:24

with any other method call. 1:29

And then additionally we can send in the block. 1:33

Now there's another way that we can call the block here, but 1:38

it involves assigning the block to a variable. 1:41

And we do that by using an ampersand and then assigning it to a variable. 1:46

In this case, we're calling the block that we send in, block. 1:52

Now, when we do that, I mean, we could save this, and run it again, 1:57

let me just go ahead and clear the screen. 2:02

We can see that it still works. 2:03

Instead of seeing yield name, when we assign a block to a variable, 2:09

we can explicitly call it by saying block.call and 2:15

passing in the argument to it. 2:23

Which in this case is the name. 2:26

So if I clear the screen and run it again, we can see we get the exact same behavior. 2:29

Now if the block didn't take an argument, in this case, its name, and 2:37

we're passing it into the block as your_name, we could just use block.call. 2:41

And if we had another variable in here, 2:48

for example, age. 2:53

If we had two variables that we wanted to send in or two arguments that we wanted to 3:04

send in to the block, we could do that this way. 3:08

Let's just clear the screen and run this again. 3:21

And that is how we would send in multiple arguments to the block. 3:27

We could do this with the yield statement as well. 3:34

Yield name and age. 3:37

And clear the screen, just make sure it runs okay. 3:40

Okay. 3:46

So there we go. 3:47

That's the same thing. 3:47

Now one other interesting thing that we get right here is another keyword which 3:49

lets us tell whether or not a block was sent in to a method. 3:56

And that is called block_given ith a question mark. 4:02

So if we send in a block we can say, yield the name and 4:13

the age if there is a block and the just return the name. 4:16

Let's just go ahead and make sure that works. 4:19

So right now we're still sending in a block. 4:22

We should see the same thing, and we do. 4:24

But if we were to comment this out, let's go ahead and 4:30

clear the screen and run it again. 4:35

And we can see it doesn't even run that. 4:36

If we wanted to, we could get even more fancy and 4:44

say, if there's a block given, well then we do all the assignment and the yield. 4:51

And if there is no block given, we'll say no block given. 5:04

Just clear the screen here. 5:13

And that works like we expect because we did supply the block. 5:16

Now if we go back and comment the block out, let's see what happens. 5:19

We just get the message saying no block given. 5:25

Great Job! 5:30

Try practicing calling blocks in different ways on your own now using WorkSpaces. 5:31

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Ruby Blocks

Calling Blocks

Code Samples