Swift #define in Extension

Question

How can i define a Constant in a Extension analogous to Objective C

Objective C:

#define integerMax NSIntegerMax

Swift:

extension NSMutableArray {
      let integerMax = Int.max  // Doesn't work

You are confusing preprocessor directives and stored properties (which you cannot add in class extension). — Kreiri, Jun 18 '14 at 08:55
Yeah, this is rather confusing code. The ObjC code doesn't even mention NSMutableArray, why would the Swift code mention it? — Catfish_Man, Jun 18 '14 at 23:54

score 6 · Answer 1 · edited May 23 '17 at 12:24

6

You can add it as a (readonly) computed property:

extension NSMutableArray {
    var integerMax : Int { get { return Int.max } }
    ...
}

see also: https://stackoverflow.com/a/25428013/2274829

Edit

A more concise version, as suggested in the comments:

extension NSMutableArray {
    var integerMax : Int { return Int.max }
    ...
}

edited May 23 '17 at 12:24

Community

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1

answered Mar 11 '15 at 12:09

GK100

3,664
1
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Not possible. `Extensions may not contain stored properties.` – SoftDesigner Sep 12 '16 at 13:15
True that Swift extensions may not contain stored properties but a read-only computed property is functionally equivalent to a constant stored property. – Mobile Dan Jan 27 '17 at 20:05
I suggest the more concise syntax `var integerMax: Int { return Int.max }`. If a stored property has only a getter then the `get` keyword and braces are not required. – Mobile Dan Jan 27 '17 at 20:09

score 1 · Answer 2 · answered Nov 11 '14 at 05:40

1

you can define first the constant. And then using it in the extension

let integerMax = Int.max
extension NSMutableArray {
    func someFunc() {
        var someVar : Int = integerMax
        //..... 
    }

answered Nov 11 '14 at 05:40

Rodrigo Gonzalez

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score 0 · Answer 3 · answered Jun 18 '14 at 08:54

I presume Extensions have the same constraint as Categories in Obj-C in that you can't add new instance variables (or in this case constants).

the #define in Obj-C is not the same as a let-generated constant in Swift. #define is a preprocessor macro which simply tells the compiler to do a find and replace on the name with the value. the let statement is in effect creating a new property on the class which you can't do in Extensions/Categories.

In Obj-C you can route around this with associated objects by using some runtime magic. I'm afraid I don't know the equivalent for Swift or even if it's possible.

Swift #define in Extension

3 Answers3