Comparing generators with Iterator objects

Comparing generators with Iterator objects

The primary advantage of generators is their simplicity. Much lessboilerplate code has to be written compared to implementing an Iterator class, and the code is generally much morereadable. For example, the following function and class are equivalent: 

<?php

function getLinesFromFile($fileName) {

    if (!$fileHandle = fopen($fileName, 'r')) {

        return;

    }

    while (false !== $line = fgets($fileHandle)) {

        yield $line;

    }

    fclose($fileHandle);

}

// versus...

class LineIterator implements Iterator {

    protected $fileHandle;

    protected $line;

    protected $i;

    public function __construct($fileName) {

        if (!$this->fileHandle = fopen($fileName, 'r')) {

            throw new RuntimeException('Couldn\'t open file "' . $fileName . '"');

        }

    }

    public function rewind() {

        fseek($this->fileHandle, 0);

        $this->line = fgets($this->fileHandle);

        $this->i = 0;

    }

    public function valid() {

        return false !== $this->line;

    }

    public function current() {

        return $this->line;

    }

    public function key() {

        return $this->i;

    }

    public function next() {

        if (false !== $this->line) {

            $this->line = fgets($this->fileHandle);

            $this->i++;

        }

    }

    public function __destruct() {

        fclose($this->fileHandle);

    }

}

?>  

This flexibility does come at a cost, however: generators are forward-onlyiterators, and cannot be rewound once iteration has started. This alsomeans that the same generator can't be iterated over multiple times: thegenerator will need to either be rebuilt by calling the generator functionagain, or cloned via the clone keyword.