CODEWITHSUNDEEP
swift
Nandin Borjigin
Nandin Borjigin

Reputation: 2154

How to initialize multiple variables of some type in one line

I want to achieve something like

var a, b, c: MyType = MyType()

but this line doesn't compile because compiler treats the type annotation MyType is only for variable c thus a and b are missing either type annotation or a initial value for type inference.

Both of followings are legal : 

// legal but verbose
var a = MyType()
var b = MyType()
var c = MyType()

// legal but verbose to initialize
var a, b, c: MyType
a = MyType()
b = MyType()
c = MyType()

These two styles I can think of are both legal but somehow verbose, especially if there are dozens of variables of same type.

Is there any elegant way to achieve this?

Upvotes: 12

Views: 19442

Answers (5)

Lucas Werner Kuipers
Lucas Werner Kuipers

Reputation: 300

Swift 5+

Some possible solution (maybe worth it if you're planning on doing this several times) is writting a struct to initialize your values and a method (or computed property) on that struct to return the individual components unpacked. You could also add a typealias for improved readability:

typealias MyTypeTrio = (a: MyType, b: MyType, c: MyType)

struct MyTypesPack {
    var a, b, c: MyType

    init(a: MyType = .init(), b: MyType = .init(), c: MyType = .init()) {
        self.a = a
        self.b = b
        self.c = c
    }

    var components: MyTypeTrio { (a, b, c) }
}

Usage:

...

let (a, b, c) = MyPackTrio().components

Of course, if you don't need that much granularity of control you may as well just add a static (or not) helper method anywhere (but preferrably in a namespace, such as in an extension of MyType, for instance).

You coud simply write:

extension MyType {
    static let trio: MyTypeTrio = (a: MyType(), b: MyType(), c: MyType())
}

and then just use it as:

var (a, b, c) = MyType.trio

I ran into a similar situation recently regarding color components.

Here's what I did then:

typealias RGBA = (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat)

struct RGBAColor {
    var red, green, blue, alpha: CGFloat

    init(red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0) {
        self.red = red
        self.green = green
        self.blue = blue
        self.alpha = alpha
    }

    var components: RGBA { (red, green, blue, alpha) }
}

Upvotes: 0

BandarAlmarri
BandarAlmarri

Reputation: 1

MyType = MyType() var MyType: [Any] = [Int, "String", "abc", Double, etc..]

Upvotes: -1

Vikash Kumar Chaubey
Vikash Kumar Chaubey

Reputation: 184

More smarter way to do this is

let type = (MyType(), MyType(), MyType())
var (a, b, c) = type

Upvotes: -3

Cœur
Cœur

Reputation: 38717

Two options in Swift: commas or tuples.

With commas separated statements:

var a = MyType(), b = MyType(), c = MyType()

With a tuple statement:

var (a, b, c) = (MyType(), MyType(), MyType())

Also, but discouraged, you can make multiple statements on one line using semi-colons:

var a = MyType(); var b = MyType(); var c = MyType()

Upvotes: 15

Adrian Bobrowski
Adrian Bobrowski

Reputation: 2794

You can declare multiple constants or multiple variables on a single line, separated by commas:

var a = "", b = "", c = ""

NOTE

If a stored value in your code is not going to change, always declare it as a constant with the let keyword. Use variables only for storing values that need to be able to change.

Documentation HERE.

In your case:

var a = MyType(), b = MyType(), c = MyType()

Upvotes: 10

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