Implement object pool pattern

object_pool/pool.go

@@ -0,0 +1,72 @@
+package main
+
+import "container/list"
+
+type Object struct {
+	ID string
+}
+
+type Pool interface {
+	Borrow() (*Object, error)
+	Return(*Object) error
+}
+
+type Allocate func() (Object, error)
+
+type implementation struct {
+	Size      int
+	SizeLimit int
+	Allocate  Allocate
+	Objects   map[Object]bool
+	FreeList  *list.List
+}
+
+func New(initSize int, limit int, alloc Allocate) (*Pool, error) {
+	p := &implementation{
+		Size:      initSize,
+		SizeLimit: limit,
+		Allocate:  alloc,
+		Objects:   nil,
+		FreeList:  list.New(),
+	}
+
+	for i := 0; i < initSize; i++ {
+		obj, err := p.Allocate()
+		if err != nil {
+			return nil, err
+		}
+
+		p.FreeList.PushFront(&obj)
+
+		p.Objects[obj] = true
+	}
+
+	return nil
+}
+
+func (p *implementation) Borrow() (*Object, error) {
+	elem := p.FreeList.Front()
+	obj := p.FreeList.Remove(elem)
+
+	p.Objects[obj] = false
+
+	return obj, nil
+}
+
+func (p *implementation) Return(ref *Object) error {
+	list.PushBack(ref)
+
+	p.Objects[*ref] = true
+
+	return nil
+}
+
+func main() {
+	p := New(0, 0, func() (Object, error) {
+		return []string{}
+	})
+
+	s, _ := p.Borrow()
+	s = append(s, "string")
+	_ = p.Return(s)
+}