Rewindable PHP Generators

Today I was refactoring some code in one of my libraries, and ended up replacing a named Iterator class with a Generator. To my surprise this changed behaviour, which I noticed due to a broken test. A test verifying that I could iterate multiple times through the iterator – good that I did write that! And so I found out that you can not actually rewind a Generator. By extension, you can also iterate through the iterator only once. If you try to rewind or iterate multiple times, you’ll get an Exception. Gah!

$generator = $myGeneratorFunction();
iterator_to_array($generator);
iterator_to_array($generator); // boom!

$generator = $myGeneratorFunction();
$generator->next();
$generator->rewind(); // boom!

Luckily, this is trivial to get around. Just make an Iterator that recreates the Generator on rewind and delegates to it. I’ve created a (extremely) little library that holds such an adapter, so I can tackle this problem without cluttering my other libraries with such a random infrastructure concern. Which of course you can use as well if you want.

$generator = new RewindableGenerator( $myGeneratorFunction );
iterator_to_array($generator);
iterator_to_array($generator); // works as expected
$generator->rewind(); // works as expected

The library is called Rewindable Generator. You can install it with Composer using the package name jeroen/rewindable-generator.