php

i often joke that php is a systems programming language that you can also use to create a home page. it’s not really true, of course; no one is going to write, say, a video driver in php. but it does highlight the fact that php has an absolute tonne of functionality that is either straight through calls to c or built-in libraries that allow us to access all sorts of operating systems features.

in this series, we’re going to leverage some of that power to write a php program that does multiple things at the same time. we’ll do that by using pcntl_fork to create a number of child processes that run simultaneously. then in part two, we’ll be looking at shmop, php’s ‘shared memory operations’, as a way to allow those processes to communicate their results.

recursion has a bad reputation amongst programmers; it’s convoluted and complicated and difficult to debug, a real footgun. it’s something you do at school (if you went to school for that sort of thing) and then never touch again if you can avoid it. which is a drag, because there’s a lot of use cases for recursion. data structures of arbitrary depth are everywhere: file systems, dom trees, that 32kb json packet your integration partner just shovelled into your api.

in this post we’re going to over two features of php that help make recursion easier: the RecursiveIterator interface, which provides us with methods and features that make writing recursive functions easier, and the dreadfully-named RecursiveIteratorIterator class which we can use to flatten down arbitrarily-deep data structures.

we’ll be building a recursive function using RecursiveArrayIterator, starting with a simple loop and working up to the full function. then we’ll look at how leverage RecursiveIteratorIterator to smash that nested array into a single level so we can extract data, either with a simple loop or a more-complex-but-powerful call to iterator_apply.

there’s an rfc vote currently underway for a number of new array functions in php8.4 (thanks to symfony station for pointing this out!). the proposal is for four new functions for finding and evaluating arrays using callables. the functions are:

• array_find()
  
• array_find_key()
  
• array_any()
  
• array_all()
  

the full details can be read here

if we’re impatient, though, we can skip waiting for php8.4 and homeroll these ourselves.