Swift Apprentice Beginning programming with Swift 4.2 by Unknown

Author:Unknown
Language: eng
Format: epub

Swift Apprentice

Chapter 12: Methods

Before you get carried away with all the power that these libraries provide, let’s continue implementing your own SimpleDate type from the ground up.

Initializers in structures

Initializers ensure all properties are set before the instance is ready to use: struct SimpleDate {

var month: String

var day: Int

init() {

month = "January"

day = 1

}

func monthsUntilWinterBreak() -> Int {

return months.index(of: "December")! -

months.index(of: month)!

}

}

If you tried to create an initializer without setting the day property, then the compiler would complain.

By creating even one custom initializer, you forgo the option to use the automatic memberwise initializer. Recall that the auto-generated memberwise initializer accepts all the properties in order as parameters, such as init(month:day:), for the SimpleDate structure. When you write a custom initializer, the compiler scraps the one created automatically.

So this code won’t work right now:

let valentinesDay = SimpleDate(month: "February",

day: 14) // Error!

Instead, you’ll have to define your own initializer with parameters:

init(month: String, day: Int) {

self.month = month

self.day = day

}

In that code, you assign the incoming parameters to the properties of the structure.

Notice how self is used to tell the compiler that you’re referring to the property rather than the local parameter.

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