30 lines
1.3 KiB
Markdown
30 lines
1.3 KiB
Markdown
|
---
|
|||
|
|
title: Constants
|
|||
|
|
---
|
|||
|
|
## Constants
|
|||
|
|
|
|||
|
|
A constant associates a name with a value of a particular type.
|
|||
|
|
|
|||
|
|
#### Example:
|
|||
|
|
```swift
|
|||
|
|
let name = "Chris Lattner"
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
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`.
|
|||
|
|
|
|||
|
|
Once you have declared a constant you don't need to use the `let` keyword anymore you just call it by its name.
|
|||
|
|
|
|||
|
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:
|
|||
|
|
```swift
|
|||
|
|
let shouldWaterFreeze: Bool // (1)
|
|||
|
|
if temperature < 0 {
|
|||
|
|
shouldWaterFreeze = true // (2)
|
|||
|
|
else {
|
|||
|
|
shouldWaterFreeze = false // (3)
|
|||
|
|
}
|
|||
|
|
```
|
|||
|
|
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).
|
|||
|
|
|
|||
|
|
#### More Information:
|
|||
|
|
- <a href='https://docs.swift.org/swift-book/LanguageGuide/TheBasics.html#ID310' target='_blank' rel='nofollow'>The Swift Programming Language</a>
|