In this article we’ll take a look at generators which provide an easy way to implement simple iterators without the overhead or complexity of the Iterator interface.

How do Generators Work?

According to Wikipedia, a generator “is very similar to a function that returns an array, in that a generator has parameters, can be called, and generates a sequence of values”. A generator is basically a normal function, but instead of returning a value it yields as many values as it needs to. It looks like a function but acts like an iterator.

Generators use the yield keyword instead of return. It acts similar to return in that it returns a value to the caller of the function, but instead of removing the function from the stack, yield saves its state. This allows the function to continue from where it was when it’s called again. In fact, you cannot return a value from a generator although you can use return without a value to terminate its execution.

The PHP manual states: “When a generator function is called, it returns an object that can be iterated over.” This is an object of the internal Generator class and implements the Iterator interface in the same way a forward-only iterator object does. As you iterate over that object, PHP calls the generator each time it needs a value. The state is saved when the generator yields so that it can be resumed when the next value is required.

Written by Stefan Froelich. Read the full article here.