All language subtitles for pragstudio-ruby-blocks-08-block_initializer (Transcribed on 27-Apr-2023 21-06-55)

We're not going to look at another block pattern that turns up in a very unexpected place.

If you've ever written a Ruby gem, then you might have seen something like this.

So we're creating a Ruby gem specification here using the specification class that's

inside of the gem module, but notice we're calling new to initialize a new object,

but the new method takes a block here.

The block parameter is S, that's the specification object that's being initialized or

created, and then inside of the block, we can just assign values to some of the attributes

of the specification.

In this particular case, I've all signed the result of all this to the spec object,

and then printed it out down below.

And if we run this, well, the 2S method in the gem spec class, it just prints out the name,

in this case it'd be my gem, and the version is 2.0.0, which is what we set up in the

block.

And the block, in this case, gives us a way to set up that object inside of a block structure

here.

So how does this work?

Well, let's try writing our own shorter version of this.

I'm going to abbreviate this a little bit because we don't need all these attributes,

right?

And because gem, the gem module, on the specification class, they've already been written,

and they're actually loaded in the Ruby programs, I'm going to change this around.

Our modules are going to be called gem with a j, and that way we won't run into any collisions

with the built-in specification class in RubyJems.

All right, let's go ahead and implement this.

We'll do it right up here.

We're going to have a module, it's called gem with a j, inside of there, we're going to have

a class called specification.

It has some attributes.

We'll have extra accessors for those.

We have name, version, and summary.

And then we have an initialized method.

Now remember, when you call new and Ruby to create a new object, new allocates the memory,

but then behind the scenes that turns around and calls the initialized method to actually

initialize that object.

So in the initialized method, we generally set attributes.

In this case, we can set the version attribute to be by default 1.0.0.

All right?

And you might do more default initialization right here, as you would, any initialized method.

But we know that this new method, we passed the block to that, and it could do some more

initialization.

So how do we pull that off?

Well, inside of our initialized method here, we just yield to the block.

We need to give it the object that's being created, which is the specification object

in this case.

We can get that by using self, inside of initialize, self is the object we're initializing.

And we only want to do that if a block was given.

So we use block underscore given, question mark there.

All right, we save that and run it.

Well now it prints out our gems specification.

I want to see what the attributes are in there.

So when it changes a little bit, I'm going to use our old friend P right there to print

out its native form.

And we see we've got a gems specification object whose version is 2.0.

Notice it's not 1.0 as up in here, because our block overwrote that version number

right here.

So our block did further initialization.

This name is my gem and the summary is, this is a cool gem.

So this block based style makes it very clear that inside of the block, all the statements

in that block are focusing on initializing this same object.

So what if we don't pass it up block?

Well we're checking if a block is given.

So we should be okay there.

If we take this block and I'm just going to comment that out right there.

So we don't have it associated.

And then we can initialize attributes as we normally were with an object say I'm going

to set the name of our gem to be something like Mike.

Well that should still work and it does.

But notice that the version now is 1.0.0 because that's the default version and the name

is now Mike.

So because we use the block given, we can associate a block or not associate a block.

So whether you want to use a block or not is really a stylistic design decision.

You can assign attributes as you normally would like this or if you want to make it very

clear that this chunk of code is all focused on initializing the object then you can

pass a block in there.

So when I was researching code for this course I was surprised how often I found this block

initialization pattern in the wild and you'll see a lot more examples of this in the exercise.

In the next section we're going to look at the final use for blocks and it's a great way

to manage resources.