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In this video, we learn a little trick with extending and including something at the same time.
Code Samples
module Inventoryable
def self.included(klass)
klass.extend(ClassMethods)
end
module ClassMethods
def create(attributes)
object = new(attributes)
instances.push(object)
return object
end
def instances
@instances ||= []
end
end
def stock_count
@stock_count ||= 0
end
def stock_count=(number)
@stock_count = number
end
def in_stock?
stock_count > 0
end
end
class Shirt
include Inventoryable
attr_accessor :attributes
def initialize(attributes)
@attributes = attributes
end
end
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When we last left off,
0:00
we had just added the stock_count
methods to our inventoriable class.
0:01
Now what we're gonna do is take the same
pattern that we used in the tracking
0:07
module to do this create and
return instances.
0:11
So, we're gonna do this
in a tricky little way.
0:17
We're gonna do it inside of another
module, inside of Inventoryable.
0:20
We're gonna call this ClassMethods
0:24
because these are going to go on
the class of what we want inventoried.
0:28
So let's go ahead and
write our create method.
0:34
And that's going to take
an attributes hash.
0:40
And this is gonna be very very
similar to what we did here.
0:45
We're gonna initialize an object, push
it to instances and return the object.
0:48
And the only difference between this and
1:06
the create method in the tracking
module is that we're
1:09
taking an attributes hash instead of
a single item, which was a string.
1:12
So now we'll be able to say, shirt.create.
1:18
But we still need to write
the instances method.
1:22
Very very easy, we just say, instances
conditionally equals a new array.
1:26
And now we can push on to that.
1:32
So, we've got this class methods module.
1:36
And what we need to do
1:41
is extend our shirt class with
it in order to get that to work.
1:43
We can say extend
Inventoryable::ClassMethods,
1:49
and now we'll get
the create method as well.
1:55
So we can say the same thing here,
Shirt.create,
2:02
Shirt.create, and this shouldn't affect
our code at all, and it should work.
2:06
Let's go ahead and
run it and see what happens.
2:13
Okay, it looks like we got
what we were expecting.
2:17
We still have these
specific shirts in stock.
2:19
New.
2:23
Take all of these out here,
and let's go ahead and
2:24
just take a look at Shirt.instances.
2:28
Just to make sure everything is in there.
2:34
So I'm gonna clear my screen and
run that again.
2:36
And we can see we have these
two instances of the shirt
2:41
class just like we expected to
by having this create method.
2:46
So this is kind of cumbersome
to keep doing each time.
2:53
Extend and include.
2:57
And, there's a pattern that a lot of Ruby
programmers use when we do something
2:59
like this.
3:03
Now, remember this included method
that we had access to before?
3:05
Where we sent in the class
that's been included?
3:10
We could take advantage of that inside
of our Inventoryable module as well.
3:14
So when we say that this module
has been included into this class,
3:20
we can get really tricky and
just tell the class to extend itself
3:27
with the class methods that
are inside of this module.
3:33
Now, if we take this out,
everything should still work.
3:39
I clear my screen and run this again.
3:44
We still get these shirts and
the create method works fine,
3:48
even though we're only
specifically including one module.
3:52
So when we include it, the class gets sent
in, which in this case is the shirt class.
3:57
So by calling shirt.extend ClassMethods,
it's the same thing
4:02
as if we extended it with
the Inventoryable class methods ourselves.
4:08
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