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Why use a generator

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Generators are useful when you need to generate a large collection to later iterate over. They’re a simpler alternative to creating a class that implements an Iterator, which is often overkill.

For example, consider the below function. 

function randomNumbers(int $length)
{
    $array = [];
    
    for ($i = 0; $i < $length; $i++) {
        $array[] = mt_rand(1, 10);
    }
    
    return $array;
}

All this function does is generates an array that’s filled with random numbers. To use it, we might do randomNumbers(10), which will give us an array of 10 random numbers. What if we want to generate one million random numbers? randomNumbers(1000000) will do that for us, but at a cost of memory. One million integers stored in an array uses approximately 33 megabytes of memory. 

$startMemory = memory_get_usage();

$randomNumbers = randomNumbers(1000000);

echo memory_get_usage() - $startMemory, ' bytes';

This is due to the entire one million random numbers being generated and returned at once, rather than one at a time. Generators are an easy way to solve this issue.

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Generators:
* Generators
* The Yield Keyword
* Reading a large file with a generator
* Why use a generator
* Using the send() function to pass values to a generator
* Re-writing randomNumbers using a generator
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