go-generics.go

package main

import (
	"fmt"
	"strings"
)

type Country struct {
	Code string
	Name string
}

func (country Country) String() string {
	return country.Code + ": " + country.Name
}

func Map[T any](items []T, mapper func(T) T) []T {
	result := make([]T, 0, len(items))

	for _, item := range items {
		result = append(result, mapper(item))
	}

	return result
}

func Filter[T any](items []T, filter func(T) bool) []T {
	var result []T

	for _, item := range items {
		if !filter(item) {
			continue
		}

		result = append(result, item)
	}

	return result
}

func Find[T any](items []T, match func(T) bool) (*T, bool) {
	for _, item := range items {
		if match(item) {
			return &item, true
		}
	}

	var empty T
	return &empty, false
}

func Print[T any](s []T) {
	for _, v := range s {
		fmt.Println(v)
	}
}

func main() {
	countries := []*Country{
		{Code: "SK", Name: "Slovakia"},
		{Code: "CZ", Name: "Czechia"},
		{Code: "HU", Name: "Hungary"},
	}

	fmt.Println("all countries:")
	Print(countries)

	countries = Map(countries, func(country *Country) *Country {
		return &Country{
			Code: strings.ToUpper(country.Code),
			Name: strings.ToUpper(country.Name),
		}
	})

	sk, found := Find(countries, func(country *Country) bool {
		return country.Code == "SK"
	})
	if found {
		fmt.Printf("\nSK found: %s\n", *sk)
	}

	fmt.Println("\nuppercase:")
	Print(countries)

	countries = Filter(countries, func(country *Country) bool {
		return country.Code != "SK"
	})

	fmt.Println("\nexcept SK:")
	Print(countries)
}