Iterator 迭代器模式:

無需知曉聚合物件的內部細節, 即可依序存取內含的每一個元素

提供一種方法依序存取一個聚合物件中各個元素, 而又不暴露該物件的內部表示

Example

https://github.com/kimi0230/DesignPatternGolang/tree/master/Iterator

package iterator

type Iterator interface {
    First() interface{}
    Next() interface{}
    IsDone() bool
    CurrentItem() interface{}
}

type ConcreteIterator struct {
    // 定義一個具體聚集物件
    aggregate *ConcreteAggregate
    current   int
}

func NewConcreteIterator(aggregate *ConcreteAggregate) *ConcreteIterator {
    return &ConcreteIterator{aggregate, 0}
}

func (c *ConcreteIterator) First() interface{} {
    return c.aggregate.items[0]
}

func (c *ConcreteIterator) Next() interface{} {
    c.current++
    if c.current < c.aggregate.Count() {
        return c.aggregate.items[c.current]
    }
    return nil
}

func (c *ConcreteIterator) IsDone() bool {
    if c.current >= c.aggregate.Count() {
        return true
    }
    return false
}

func (c *ConcreteIterator) CurrentItem() interface{} {
    if c == nil {
        return nil
    }
    return c.aggregate.items[c.current]
}

type Aggregate interface {
    CreateIterator()
}

type Object struct {
    Name string
}

type ConcreteAggregate struct {
    items []Object
}

func NewConcreteAggregate() *ConcreteAggregate {
    return new(ConcreteAggregate)
}

func (c *ConcreteAggregate) Count() int {
    return len(c.items)
}

func (c *ConcreteAggregate) GetThis(index int) Object {
    if c == nil {
        return Object{}
    }

    return c.items[index]
}

// SetThis : Insert 到指定 index
func (c *ConcreteAggregate) SetThis(index int, val Object) {
    if c == nil {
        return
    }
    // 先要一組記憶體空間
    tmpObject := Object{}
    c.items = append(c.items, tmpObject)
    copy(c.items[index+1:], c.items[index:])
    c.items[index] = val
}