Edd Mann has a new post today looking at implementing streams in your PHP applications. In this case we're not talking about the streams built into PHP but the concept of a source of information that only produces the next item when requested (aka "lazy loading").
Typically, when we think about a list of elements we assume there is both a start and finite end. In this example the list has been precomputed and stored for subsequent traversal and transformation. If instead, we replaced the finite ending with a promise to return the next element in the sequence, we would have the architecture to provide infinite lists. Not only would these lists be capable of generating infinite elements, but they would also be lazy, only producing the next element in the sequence when absolutely required. This concept is called a Stream, commonly also referred to as a lazy list, and is a foundational concept in languages such as Haskell.
He talks about how streams of data should be interacted with differently than a finite list of data and the promises they're based on to provide the right data. He shows two different approaches to implementing a an object to stream data from - a class-based method and one that uses generators. Sample code is provided for each with the generator approach being a bit shorter as they're designed to lazy load items as requested.