-Hi! In this video, we are going to look at two extremely important features
in the object-oriented language, which are senders and implementors.
In order to understand what they mean,
let us open the System Browser.
Once again, go to Tools, then System Browser.
We will go to a package, let us say in AST-Core.
We will go to our RBComment, and we will look at the size.
If you right click on the method Size,
you will see that the Implementors and Senders options show up.
So, what are the implementors of size?
Basically, the implementors of size, if we look at them,
will be all of the different classes, and their associated packages,
that implement a method called "size".
We can see that we have quite a lot of them, 109.
We can look inside them.
For example, LGitDiffFile, Pointer Layout, RBComment.
But if we look at it,
we can see that we have the package from which it is defined,
so System-Sources, the class SourceFile,
and we can simply browse it by clicking on Browse.
It will open another System Browser on the correct class method.
So, the implementors are all the different classes
that have size method defined.
Now, if we look at the senders...
So, Senders...
We can see that the senders of size
are all the methods that call "size" in their body.
For example, here, we have "at:put:" that shows its "size",
we have "extendMaxAsciiTo:"...
So, any method, basically, that will call "size" in its body.
This is really useful, because implementors will show you
all the classes that define a method of the same name
and how it can be used, while senders will show you examples
of how the method "size" is used concretely.
So, in order to have a quicker access to them,
you can see that there are some shortcuts.
So, basically, implementors... This is the M, right there, that is used.
So, Cmd+M will open the implementors.
While the senders... N will be the shortcut.
So, Cmd+N.
So, senders and implementors will really help you
understand the method you do not understand.
You will see how it is used, and I really encourage you to learn
both the shortcuts and how to use them,
just to navigate and to understand the structure and class better.