在迭代器模式中实现`continue`关键字答案

【问题标题】：Implementation of `continue` keyword inside iterator pattern在迭代器模式中实现`continue`关键字
【发布时间】：2021-09-12 02:25:33
【问题描述】：

我发现continue 功能只能通过递归在迭代器模式中实现。问题当然是循环数百万个应继续的无效元素应该非常慢或堆栈溢出。

如何在不使用迭代器模式内递归的情况下实现continue关键字？

带有递归的 PHP 代码：

class TableIterator implements \Iterator
{
    private $row;
    private $fileLines;

    public function __construct()
    {
        $this->fileLines = [
            "1, 2, 3, 4, 5, 6, 7, 8",
            "my condition, 9, 10, 11, 12, 13, 14, 15",
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "24, 25, 26, 27, 28, 29, 30, 31",
            "32, 33, 34, 35, 36, 37, my condition 2, 38",
            "39, 40, 41, 42, 43, 44, 45, 46"
        ];
    }

    public function rewind(): void
    {
        reset($this->fileLines);
    }

    public function current(): array
    {
        return $this->row;
    }

    public function key(): int
    {
        return key($this->fileLines);
    }

    public function next(): void
    {
        next($this->fileLines);
    }

    public function valid(): bool
    {
        $this->row = explode(", ", current($this->fileLines));

        if($this->row[0] === 'my condition')
            $this->continue(); // here is the recursion problem
        
        if($this->row[6] === 'my condition 2')
            return false;

        return true;
    }
    
    private function continue()
    {
        $this->next();
        $this->valid();
    }
}

foreach(new TableIterator() as $key => $value)
    print_r($value);

如果有 PHP 的解决方案或 hack，我会很高兴。谢谢。

【问题讨论】：

标签： php iterator continue

【解决方案1】：

我想出了一些解决方法，但它仍然不是理想的解决方案！

问题可能是是否有任何解决方案？

if($value === null) continue; 继续迭代。评论它以获取空值并且仍然能够获取密钥。问题可能出在空值是预期值时！

class TableIterator implements \Iterator
{
    private $row;
    private $fileLines;
    private $continue;

    public function __construct()
    {
        $this->fileLines = [
            "1, 2, 3, 4, 5, 6, 7, 8",
            "my condition, 9, 10, 11, 12, 13, 14, 15",
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "24, 25, 26, 27, 28, 29, 30, 31",
            "32, 33, 34, 35, 36, 37, my condition 2, 38",
            "39, 40, 41, 42, 43, 44, 45, 46"
        ];
    }

    public function rewind(): void
    {
        reset($this->fileLines);
    }

    public function current(): ?array
    {
        if($this->continue)
        {
            $this->continue = false;
            return null;
        }
        
        return $this->row;
    }

    public function key(): int
    {
        return key($this->fileLines);
    }

    public function next(): void
    {
        next($this->fileLines);
    }

    public function valid(): bool
    {
        $this->row = explode(", ", current($this->fileLines));

        if($this->row[0] === 'my condition')
            $this->continue = true;
        
        if($this->row[6] === 'my condition 2')
            return false;

        return true;
    }
}

foreach(new TableIterator() as $key => $value)
{
    if($value === null) continue;
    var_dump($value);
}

【讨论】：

【解决方案2】：

这就是解决方案！

我不会在 2021 年费心去解释它。如果你好奇，可以爬取整个算法。

class TableIterator implements \Iterator
{
    private $row;
    private $fileLines;

    public function __construct()
    {
        $this->fileLines = [
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "1, 2, 3, 4, 5, 6, 7, 8",
            "my condition, 9, 10, 11, 12, 13, 14, 15",
            "my condition, 16, 17, 18, 19, 20, 21, 22, 23",
            "24, 25, 26, 27, 28, 29, 30, 31",
            "32, 33, 34, 35, 36, 37, my condition 2, 38",
            "39, 40, 41, 42, 43, 44, 45, 46"
        ];
    }

    public function rewind(): void
    {
        reset($this->fileLines);
        
        while($this->continue())
        {
            next($this->fileLines);
        }
    }

    public function current(): array
    {
        return $this->row;
    }

    public function key(): int
    {
        return key($this->fileLines);
    }

    public function next(): void
    {
        do {
            next($this->fileLines);
        }
        while($this->continue());
    }

    public function valid(): bool
    {
        if($this->row[6] === 'my condition 2')
            return false;

        return true;
    }
    
    private function continue()
    {
        $this->row = explode(", ", current($this->fileLines));
        
        return $this->row[0] === 'my condition' ? true : false;
    }
}

foreach(new TableIterator() as $key => $value)
{
    var_dump($value);
}

【讨论】：