Swift Q & A


What are constants in Swift?

In Swift, a constant is a variable-like entity that holds a value, but once assigned, its value cannot be changed throughout the program’s execution. Constants are declared using the `let` keyword followed by a name, an optional type annotation, and an initial value. Here’s the basic syntax:

let constantName: DataType = initialValue

`let`: This keyword indicates that you are declaring a constant, which means its value remains fixed after assignment.

`constantName`: Replace this with the name you want to give to your constant, following Swift’s naming conventions.

`DataType`: Optionally, you can specify the data type of the constant. Similar to variables, Swift can infer the data type from the initial value, so you can omit it if Swift can deduce it.

– `initialValue`: This is the initial value you want to assign to the constant. If you specify the data type, the value must be of that type. If you omit the data type, Swift will infer it from the value you provide.


Here are a few examples:

let pi: Double = 3.14159  // Declaring a constant for the mathematical constant Pi
let appName = "MyApp"    // Declaring a string constant without specifying the data type (Swift infers it's a String)

Constants are useful when you have values that should not change during the execution of your program, such as mathematical constants, configuration settings, or values that represent unchanging aspects of your application. By using constants, you make your code more readable and maintainable while ensuring that the values you depend on remain consistent throughout your program’s execution.


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Experienced iOS Engineer with 7+ years mastering Swift. Created fintech solutions, enhanced biopharma apps, and transformed retail experiences.