A Tour of Go/Generic types excercise

main.go

package main

import "fmt"

// List represents a singly-linked list that holds
// values of any type.
type List[T any] struct {
	next *List[T]
	val  T
}

func (xs *List[T]) String() string {
	if xs.next == nil {
		return fmt.Sprintf("{ val: %v, next: <nil> }", xs.val)
	} else {
		return fmt.Sprintf("{ val: %v, next: %s }", xs.val, fmt.Sprint(xs.next))
	}
}

func Append[T any](xs *List[T], x T) *List[T] {
	if xs.next == nil {
		xs.next = NewList(x)
		return xs
	} else {
		// ys is a pointer to xs, so when "moving" the current(ys) pointer down the
		// list, we "keep" the original starting pointer in xs
		//
    // Step by step:
		// xs := { val: 3, next: { val: 2, next: <nil> } }
		// ys := { val: 3, next: { val: 2, next: <nil> } }
		// ys.next = { val: 2, next: <nil> } 				        (== xs.next)
		// ys = Append(ys.next, x) 							            (ys = ys.next)
		// ys = { val: 2, next: { val: x, next: <nil> } } 	(== xs.next)
		// xs = { val: 3, next: { val: 2, next: { val: x, next: <nil> } } }
		
		ys := xs
		ys = Append(ys.next, x)
		return xs
	}
}

// Create a list with a starting value
func NewList[T any](val T) *List[T] {
	xs := new(List[T])
	xs.val = val
	xs.next = nil
	return xs
}

func main() {
	xs := NewList(0)
	fmt.Println(xs)
	
	for i := 1; i < 5; i++ {
		xs = Append(xs, i)
		fmt.Println(xs)
	}
}