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