CODEWITHSUNDEEP
swiftstructenumsconstants
Jens Kohl
Jens Kohl

Reputation: 5969

What does "static" imply on constant within an enum or struct

I recently came across the following:

enum MyEnum {
  static let myVariable = "some value"
}

struct MyStruct {
  static let myVariable = "some value"
}

and wonder what the static implies. To my understanding let already implies the immutability which is then shared by all instances of the enum/struct. It sounds to me that this is micromanaging memory consumption, but I'm not sure that I'm missing the underlying point here.

Upvotes: 2

Views: 639

Answers (1)

Airspeed Velocity
Airspeed Velocity

Reputation: 40963

It means myVariable is a type property – a single property that all instances of the type can use. Essentially a global variable associated with MyEnum.

In the case of constants declared with let, this is a way of declaring constants that are scoped to the type that don’t take up space within each instance of that type, i.e.:

struct MySlimStruct {
    static let myVariable = "some value"
}

sizeof(MySlimStruct)  // returns 0

struct MyFatStruct {
    let myVariable = "some value"
}

sizeof(MyFatStruct)  // returns 24

In the case of static variables declared with var, this is a good way of introducing undiagnosable bugs and crashes into your program.

Upvotes: 3

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