WEBVTT

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Hello everyone.

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In this course,
we'll learn about the method Yourself.

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It is seemingly useless,
and yet it's very useful.

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Let's start with an exercise.

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For this expression, Set new add: 2,

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we'd like to get a set
containing the value 2

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so that it returns only the value 2.

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Why do you get the value 2
rather than a set containing 2?

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If you look at the method add:
implemented in the class Set,

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you can see it returns its parameter.

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In the expression Set new add: 2,

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the expression Set
returns the class Set.

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When you send new to the class Set,
it returns a new set.

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Set new add: 2

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returns the value returned by add: 2,
which is 2.

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The set is lost.

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To solve this problem,

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you can describe the expressions
step by step.

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You can create a temporary variable:
you declare the variable s.

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Assign the new Set to s.

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Add 2 to s.

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s now contains
a set which contains the value 2.

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It's what we wanted.

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You can simplify these expressions

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by using the method yourself.

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If you take a closer look,

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you'll see it contains only one thing:
return self.

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Return self being optional,
this method could also be empty

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and do nothing
except returning its receiver.

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This method seemingly
only returns its receiver.

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And yet, it's useful in such cases

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thanks to the operator cascade.

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After adding 2,

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let's execute the method yourself

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which will return the receiver

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so that the full expression
can be the receiver,

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which is the new Set.

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If I take Set new,

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which is the new Set,

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and write add: 2 applied to Set new,

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it returns 2.

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But thanks to the operator cascade
followed by yourself,

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the expression
as a whole returns the new Set.

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Why does the cascade
systematically return

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the value its last expression returns?

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The cascade, in this case,

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returns the value yourself returns.

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We often use yourself and the cascade

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in the methods of instantiation.

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These are class methods

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of messages to be sent to classes

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which return new instances.

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To create a new Set

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which contains an object by default,

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I can send the message with: anObject
to Set.

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This code is executed
to create a new Set,

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to put it in the variable instance,

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to add to instance the new parameter,

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and to return instance.

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I can write this expression as a whole
by using yourself

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in a shorter and more idiomatic way.

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This code is typically found in Pharo.

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It's important to master the semicolon,

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the cascade, and yourself.

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What you must remember
at the end of this course

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is that some methods,
even though they're very simple,

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can be very powerful and used a lot.

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The cascade, the semicolon,
and the method yourself

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are very often used together

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to make sure a complete expression

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returns the expected value.