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- Hello again and welcome to lesson four.

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In this lesson, we're going
to talk all about enums.

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An enum is a data type

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that only permits a
restricted set of values.

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Enums are an important part
of Rust, as you'll see,

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and you can't get very far
without knowing how they work.

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So we'll begin by showing the syntax

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for defining and using simple enums,

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and how to avoid warning messages

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when you're getting started.

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Then we'll take it a step further

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and see how to define enums
that convey data values.

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We'll explore the syntax and
discuss why this is useful.

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We'll wrap up the lesson by
discussing two standard enums

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in the vast library, the option enum,

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which represents a possibly empty valley,

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and the result enum,

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which represents a
possible error condition.