设计模式——迭代器模式

说明

示例

下面看下代码实现

interface Collection{
    public function iterator();
    public function get(int $i);
    public function size(): int;
}

interface Iterator{
    public function previous();
    public function next();
    public function hasNext(): bool;
    public function first();
}

class MyCollection implements Collection{
    public string $str = 'ABCDE';
    public function iterator(): MyIterator{
        return new MyIterator($this);
    }
    public function get(int $i): string{
        return $this->str[$i];
    }
    public function size(): int{
        return strlen($this->str);
    }
}

class MyIterator implements Iterator{
    private Collection $collection;
    private int $pos = -1;
    public function __construct(Collection $collection){
        $this->collection = $collection;
    }

    public function previous(){
        if ($this->pos > 0){
            $this->pos--;
        }
        return $this->collection->get($this->pos);
    }

    public function next(){
        if ($this->pos < $this->collection->size() - 1){
            $this->pos++;
        }
        return $this->collection->get($this->pos);
    }

    public function hasNext(): bool{
        return $this->pos < $this->collection->size() - 1;
    }

    public function first(){
        $this->pos = 0;
        return $this->collection->get($this->pos);
    }
}


// 调用
$collection = new MyCollection();
$it = $collection->iterator();
while ($it->hasNext()){
    echo $it->next().'&nbsp;&nbsp;';
}
// output: A  B  C  D  E

总结