In a recent post to the LeaseWebLabs blog Maurits van der Schee looks at the use of the "yield" keyword in PHP 5.5 to work with generators. 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 but it yields values one at a time.

The concept of generators is not new. The “yield” keyword exists in other programming languages as well. As far as I know C#, Ruby, Python, and JavaScript have this keyword. The first usage that comes to mind for me is when I want to read a big text file line-by-line (for instance a log file). Instead of reading the whole text file into RAM you can use an iterator and still have a simple program flow containing a “foreach” loop that iterates over all the lines.

He includes a few code examples showing a class that can read in data from a file in chunks and output the lines as they're extracted (versus using something like file). He also talks about a small performance comparison in working with the file pointer, fread over fgets. He even makes a simple benchmark script to compare the overall time and memory consumption of the fetching of different byte "chunks" from the file.