What is the difference between convenience init vs init in swift, explicit examples better

Question

I am having troubles to understand the difference between both, or the purpose of the convenience init.

Answer 1

Note: Read The whole Text

Designated initializers are the primary initializers for a class. A designated initializer fully initializes all properties introduced by that class and calls an appropriate superclass initializer to continue the initialization process up to the superclass chain.

Convenience initializers are secondary, supporting initializers for a class. You can define a convenience initializer to call a designated initializer from the same class as the convenience initializer with some of the designated initializer’s parameters set to default.

Designated initializers for classes are written in the same way as simple initializers for value types:

init(parameters) {
statements
}

Convenience initializers are written in the same style, but with the convenience modifier placed before the init keyword, separated by a space:

convenience init(parameters) {
statements
}

A practical Example are as follow:

class Food {
var name: String
init(name: String) {
    self.name = name
}
convenience init() {
    self.init(name: "[Unnamed]")
}
}
let namedMeat = Food(name: "Bacon")
// namedMeat's name is "Bacon”

The init(name: String) initializer from the Food class is provided as a designated initializer because it ensures that all stored properties of a new Food instance are fully initialized. The Food class does not have a superclass, and so the init(name: String) initializer does not need to call super.init() to complete its initialization.

“The Food class also provides a convenience initializer, init(), with no arguments. The init() initializer provides a default placeholder name for a new food by delegating across to the Food class’s init(name: String) with a name value of [Unnamed]:”

“let mysteryMeat = Food()
// mysteryMeat's name is "[Unnamed]”

The second class in the hierarchy is a subclass of Food called RecipeIngredient. The RecipeIngredient class models an ingredient in a cooking recipe. It introduces an Int property called quantity (in addition to the name property it inherits from Food) and defines two initializers for creating RecipeIngredient instances:

class RecipeIngredient: Food {
var quantity: Int
init(name: String, quantity: Int) {
    self.quantity = quantity
    super.init(name: name)
}
override convenience init(name: String) {
    self.init(name: name, quantity: 1)
}
}

The RecipeIngredient class has a single designated initializer, init(name: String, quantity: Int), which can be used to populate all of the properties of a new RecipeIngredient instance. This initializer starts by assigning the passed quantity argument to the quantity property, which is the only new property introduced by RecipeIngredient. After doing so, the initializer delegates up to the init(name: String) initializer of the Food class.

page:536 Excerpt From: Apple Inc. “The Swift Programming Language (Swift 4).” iBooks. https://itunes.apple.com/pk/book/the-swift-programming-language-swift-4-0-3/id881256329?mt=11