WEBVTT

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Hello. In this session,
we will learn about return.

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How can you return a value

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from a block or method?

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And what are the default return values?

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There are four cases to study:

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a method which uses the caret to return,

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a method without the caret,

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a block with the caret,

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and a block without the caret.

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In a method,

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if you use the caret to return a value,

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here, it will return

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a specific value.

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It will exit the method.

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If I don't use the caret,

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the method returns self by default.

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This part is optional.
You don't usually write it.

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The return value of a block
is its last expression.

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In the case of this block,

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between these, I have a block

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which takes a value x as a parameter.

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I add 33 to x.

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The value, the result
of this expression x+33

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is not used, so it was erased.

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The following instruction is x+2,
so I add 2 to the value x.

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As it's the block's last expression,

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its value

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represents the return value
of the block.

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So my block, value:5.

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It means I execute the block

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with x taking the value 5.

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So I compute 33+5;

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the result gets erased,
since it's useless.

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5+2 gives the value 7

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which is used
as the block's return value.

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So the entire expression's value is 7.

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If I use the caret in a block,

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the behavior is totally different
from a method.

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You shouldn't expect
the block to be terminated,

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but the method.

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Let's look at the example
of the method factorial

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in the class Integer.

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There's one return here and one there.

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These two returns
terminate the method's execution.

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So if the receiver self is zero

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during the execution of the method,

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the block is executed,

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1 is immediately returned,
and the method will terminate.

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So the method returns 1.

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return is not used to terminate
the block but the embracing method.

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In the second example,
if self is bigger than zero,

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you compute with a recursive call

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and immediately return the result.

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So the method
doesn't continue to execute

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when self is bigger than zero.

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In the other cases,
if you reach the third instruction,

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you get an error message, meaning
that the receiver is a negative number.

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You should remember

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that the caret allows you
to terminate the method

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whether caret is located in the method
or in the block in the method.

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The caret always terminates the method

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and returns a value
specified after the caret.

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By default, a method returns self.

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It's useless to write method self
at the end

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as it is the value
which is returned by default.

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A block returns the result
of its last expression.