package main

import "fmt"

func getKeys(m any) ([]any, error) {
	switch t := m.(type) {
	default:
		return nil, fmt.Errorf("unknown type: %T", t)
	case map[string]int:
		var keys []any
		for k := range t {
			keys = append(keys, k)
		}
		return keys, nil
	case map[int]string:
		// ...
	}

	return nil, nil
}

func getKeysGenerics[K comparable, V any](m map[K]V) []K {
	var keys []K
	for k := range m {
		keys = append(keys, k)
	}
	return keys
}

type customConstraint interface {
	~int | ~string <1>
}

func getKeysWithConstraing[K customConstraint, V any](m map[K]V) []K {
	return nil
}

type Node[T any] struct {
	Val  T
	next *Node[T]
}

func (n *Node[T]) Add(next *Node[T]) {
	n.next = next
}

type sliceFn[T any] struct {
	s       []T
	compare func(T, T) bool
}

func (s sliceFn[T]) Len() int           { return len(s.s) }
func (s sliceFn[T]) Less(i, j int) bool { return s.compare(s.s[i], s.s[j]) }
func (s sliceFn[T]) Swap(i, j int)      { s.s[i], s.s[j] = s.s[j], s.s[i] }