In this post to his site Mark Baker has shared some "sending gotchas" when generators are used in you PHP code. The focus of the article is on the "sending" part, pushing data into the generator for evaluation and use.

If you’re reading this, you’re probably already aware of just how useful PHP’s Generators are for improving performance and/or reducing memory overheads while keeping your code clean and easy to read.

Unlike their equivalent in some programming languages, PHP’s Generators allow you to send data into the Generator itself; not simply at initialisation (the arguments that we pass to the Generator when instantiating it); but also between iterations. This has its own uses, and again, allows us to move code from our main blocks and methods into the Generator itself. [...] However, there are a few “gotchas” when we combine Generators that both return and accept data in this way, and it really helps to be aware of them when we’re developing, otherwise it can create problems.

He starts simple, showing a generator that uses integers passed in as the starting number and addition interval for each loop. He gets a bit more complex in his next example, having a method called inside the loop. While the first instance of this behaves as expected, the second (after minor modification) yields unexpected results. He walks you through what's happening to produce those results and one possibility on how to get it corrected.