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swiftstructnested
Vic W.
Vic W.

Reputation: 837

Swift nested structures -- how to access element

In a Swift app, I am attempting to nest structures for greater clarity. Here is the code:

struct ColorStruct {
    var colorname: String = ""
    struct RGB {
        var red:   Int = 0
        var green: Int = 0
        var blue:  Int = 0
    }
}

I can access a ColorStruct element (example: "colorname") as long as it isn't nested.

Q: What am I failing to understanding about how to properly access the "red" variable?

var newColor = ColorStruct()
newColor.colorname = "Red"
newColor.RGB.red   = 255     // Results in error:
// Static member 'RGB' cannot be used on instance of type `ColorStruct`

Upvotes: 3

Views: 6370

Answers (5)

J. Doe
J. Doe

Reputation: 13033

This line:

struct RGB{ var red: Int = 0}

states that red is an instance variable in a struct RGB (with other words, red does belong to an instance of RGB). When you create a struct of type ColorStruct, you do not create a struct RGB. You can only access instance variabele if you have created an object of it. If you want to access the variabele red, create a struct RGB (RGB()), or make the variabele/struct (is this possible in Swift?) static (don't make it an instance variabele).

Upvotes: 2

Sandeep
Sandeep

Reputation: 21144

You cannot assign value to struct just like that. Either create a new property of RGB like so,

struct ColorStruct {
  var colorname:String    = ""
  var rgb = RGB()

  struct RGB {
    var red:            Int    = 0
    var green:          Int    = 0
    var blue:           Int    = 0
  }

}

var newColor = ColorStruct()
newColor.colorname = "Red"
newColor.rgb.red   = 255     // Results in error:

Or, make static variable inside ColorStruct,

struct ColorStruct {
  var colorname:String    = ""
  static var rgb = RGB()

  struct RGB {
    var red:            Int    = 0
    var green:          Int    = 0
    var blue:           Int    = 0
  }
}

ColorStruct.rgb.red = 255

Upvotes: 1

sebastien FCT
sebastien FCT

Reputation: 630

You must instantiate your RGB struct instead of ColorStruct:

struct ColorStruct {
    var colorname:String    = ""
    struct RGB              {
        var red:            Int    = 0
        var green:          Int    = 0
        var blue:           Int    = 0
    }
}

var newColor = ColorStruct.RGB()
newColor.red = 255

Upvotes: 0

Max Desiatov
Max Desiatov

Reputation: 5565

A nested struct as given in the question code doesn't automatically create an outer struct member of that type. To achieve that, refine the code this way:

struct ColorStruct {
  var colorname: String = ""
  struct RGB {
    var red:   Int = 0
    var green: Int = 0
    var blue:  Int = 0
  }

  var rgb = RGB()
}

var color = ColorStruct()
color.rgb.red = 255

Upvotes: 6

Agent Smith
Agent Smith

Reputation: 2913

You can achieve it by this:

struct ColorStruct {
var colorname:String  = ""
var colorValue: RGB!

struct RGB              {
    var red:            Int    = 0
    var green:          Int    = 0
    var blue:           Int    = 0

    mutating func setRed(value: Int) {
        self.red = value
    }
    mutating func setGreen(value: Int) {
        self.green = value
    }
    mutating func setBlue(value: Int) {
        self.blue = value
    }
}
}

And then use the struct as: 

var color = ColorStruct()

color.colorname = "blue"
color.colorValue = ColorStruct.RGB.init(red: 0, green: 0, blue: 1)
print(color.colorValue)

And if you want to change a value call this :

color.colorValue.setRed(value: 2)
print(color.colorValue)

Hope it helps

Upvotes: 0

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