Collection

package main

import (
	"fmt"
)

func main() {
	exampleDefault()
	exampleCustomTypedCollection()
}

func exampleDefault() {
	c := Collection{data: make(map[int]Identifiable)}
	c.Set(Item{ID: 123})
	c.Set(Foo{ID: 234})

	fmt.Printf("%#v\n", c)
	entity, ok := c.Get(123)
	fmt.Printf("%#v %v\n", entity, ok)

	entity, ok = c.Get(234)
	fmt.Printf("%#v %v\n", entity, ok)

	entity, ok = c.Get(999)
	fmt.Printf("%#v %v\n", entity, ok)
}

func exampleCustomTypedCollection() {
	c := NewFooCollection()
	c.Set(Foo{ID: 123})
	fmt.Printf("%#v\n", c)

	entity, ok := c.Get(123)
	fmt.Printf("%#v %v\n", entity, ok)

	entity, ok = c.Get(456)
	fmt.Printf("%#v %v\n", entity, ok)
}

// Interfaces.

type Identifiable interface {
	Identify() int
}

type Collectable interface {
	Get(id int) (entity Identifiable, ok bool)
	Set(entity Identifiable)
}

// Base collection.

type Collection struct {
	data map[int]Identifiable
}

func (collection Collection) Get(id int) (entity Identifiable, ok bool) {
	entity, ok = collection.data[id]

	return
}

func (collection Collection) Set(entity Identifiable) {
	collection.data[entity.Identify()] = entity
}

// Collection item.

type Item struct {
	ID    int
	Value string
}

func (item Item) Identify() int {
	return item.ID
}

// Typed collection.

type FooCollection struct {
	Collection
}

func NewFooCollection() FooCollection {
	return FooCollection{Collection: Collection{data: make(map[int]Identifiable)}}
}

// Typed collection item.

type Foo struct {
	ID   int
	Data string
}

func (foo Foo) Identify() int {
	return foo.ID
}