30 lines
1.3 KiB
Markdown
30 lines
1.3 KiB
Markdown
---
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title: Constants
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---
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## Constants
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A constant associates a name with a value of a particular type.
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#### Example:
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```swift
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let name = "Chris Lattner"
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```
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You declare constants with the `let` keyword then give it a name `name` then you use an assignment operator `=` to assign the value `"Chris Lattner"` to the constant `name`.
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Once you have declared a constant you don't need to use the `let` keyword anymore you just call it by its name.
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The value of a constant can’t be changed once it’s _set_. With that being said, it is important to note that the Swift compiler is smart enough to understand the difference between _declaring_ a constant, and _assigning_ a value to it. Consider the following code snippet:
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```swift
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let shouldWaterFreeze: Bool // (1)
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if temperature < 0 {
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shouldWaterFreeze = true // (2)
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else {
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shouldWaterFreeze = false // (3)
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}
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```
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The snippet above is valid and compiles with no problems (given that we have declared and assigned an `Int` value to `temparature` somewhere earlier). Notice that we _declare_ the constant in (1), and then _assign_ a value to it (2) or (3).
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#### More Information:
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- <a href='https://docs.swift.org/swift-book/LanguageGuide/TheBasics.html#ID310' target='_blank' rel='nofollow'>The Swift Programming Language</a>
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