Swift Language Initializers Customizing initialization with paramaters
Example
struct MetricDistance {
var distanceInMeters: Double
init(fromCentimeters centimeters: Double) {
distanceInMeters = centimeters / 100
}
init(fromKilometers kilos: Double) {
distanceInMeters = kilos * 1000
}
}
let myDistance = MetricDistance(fromCentimeters: 42)
// myDistance.distanceInMeters is 0.42
let myOtherDistance = MetricDistance(fromKilometers: 42)
// myOtherDistance.distanceInMeters is 42000
Note that you cannot omit the parameter labels:
let myBadDistance = MetricDistance(42) // error: argument labels do not match any available overloads
In order to allow omission of parameter labels, use an underscore _ as the label:
struct MetricDistance {
var distanceInMeters: Double
init(_ meters: Double) {
distanceInMeters = meters
}
}
let myDistance = MetricDistance(42) // distanceInMeters = 42
If your argument labels share names with one or more properties, use self to explicitly set the property values:
struct Color {
var red, green, blue: Double
init(red: Double, green: Double, blue: Double) {
self.red = red
self.green = green
self.blue = blue
}
}
