CODEWITHSUNDEEP
swiftgenerics
user14302744
user14302744

Reputation:

What is the difference between <T> and Tree<T> here? I am quite confused here

I don't quite understand when to state Tree<T> and when just T

class Tree<T> {
    var value: T

    private (set) var children: [Tree<T>] = []

    init(value: T) {
        self.value = value
    }
  
    func addChild(value: T) -> Tree<T> {
        let newChild = Tree<T>(value: value)
        children.append(newChild)
        return newChild
    }
}

Upvotes: 0

Views: 46

Answers (1)

David Pasztor
David Pasztor

Reputation: 54775

The <T> makes Tree a generic type and declares the generic type parameter called T. If you want to declare a property as type Tree, you need to write it as Tree<T>. However, if you want to use the type of a tree node, then you need to use T.

When you declare value, you simply want to store the generic value, so its type needs to be T. However, the children array stores an array of trees, so you need to declare it as [Tree<T>], not just [T].

For each instance of Tree, the generic type parameter T might be different. By naming the generic type parameter something more meaningful, such as Value, this will become much more clear.

class Tree<Value> {
    var value: Value

    private (set) var children: [Tree<Value>] = []

    init(value: Value) {
        self.value = value
    }
  
    func addChild(value: Value) -> Tree<Value> {
        let newChild = Tree<Value>(value: value)
        children.append(newChild)
        return newChild
    }
}

let intTree = Tree(value: 1) // `Value` is of type `Int` here, but you don't need to specify it, the compiler can infer it
let stringTree = Tree(value: "value") // `Value` is of type `String` here

Upvotes: 1

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