3

on Swift String is a struct and you could just initialize it using

var someString:String = "Hello"

how would I make another Struct initializable like String?

for example

struct StringV2 {
    init()
}

class SomeClass {
    let someStringV2:StringV2 = "Hello"
}

Since that's how String's code looks like.

Zonily Jame
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  • I think this might help you http://stackoverflow.com/questions/25112081/is-string-type-a-class-or-a-struct-or-something-else – Rajan Maheshwari Nov 02 '16 at 06:40
  • For Swift 2 you'll find an example here: http://stackoverflow.com/a/27713005/1187415. – Martin R Nov 02 '16 at 06:54
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    We don't know what your intentions are, but writing up a new string type is a pretty niche thing that pretty much never comes up. Most likely what you're trying to achieve can be more easily, and better, done using an extension. – Alexander Nov 02 '16 at 07:09
  • @AlexanderMomchliov yep I know of extensions but right now I'm just trying to make a new string type. for learning purposes :) – Zonily Jame Nov 02 '16 at 07:49

1 Answers1

5

This is (in my opinion) neat part of the language. Yes, this is possible, thanks to the ExpressibleByStringLiteral protocol.

Unfortunately, there is some complexity to it. ExpressibleByStringLiteral inherits from ExpressibleByExtendedGraphemeClusterLiteral, which itself inherits from ExpressibleByUnicodeScalarLiteral. Thus, to conform to the first, you must conform to the other 2 above it.

This makes it possible for your struct or class to be initialized from:

  • A UnicodeScalarLiteralType (such as a UnicodeScalar, which is a single Unicode code point, e.g. "A")
  • An ExtendedGraphemeClusterLiteralType (such as a Character, which is a collection of UnicodeScalars, such as "")
  • A StringLiteralType (such as String, which is a collection of Characters, such as "This is a string")

Here's an example implementation that just sets a String member variable:

struct StringV2: ExpressibleByStringLiteral {
    let s: String

    init(unicodeScalarLiteral: UnicodeScalar) {
        s = String(unicodeScalarLiteral)
    }

    init(extendedGraphemeClusterLiteral: Character) {
        s = String(extendedGraphemeClusterLiteral)
    }

    init(stringLiteral: String) {
        s = stringLiteral
    }
}

let s1: StringV2 = "This is a string" // String
print(s1.s)

let s2: StringV2 = "A" // Unicode scalar
print(s2.s)

let s3: StringV2 = "" // Extended grapheme cluster
print(s3.s)
Alexander
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