Channel Directions in PHP

In PHP, we don’t have direct equivalents for channels or goroutines. However, we can simulate similar behavior using arrays and functions. Here’s how we might approach this:

<?php

// This `ping` function only accepts an array reference for adding
// values. It simulates sending a message to a channel.
function ping(&$pings, $msg) {
    $pings[] = $msg;
}

// The `pong` function accepts two array references, one for
// receiving ($pings) and one for sending ($pongs).
function pong(&$pings, &$pongs) {
    $msg = array_shift($pings);
    $pongs[] = $msg;
}

function main() {
    $pings = [];
    $pongs = [];
    
    ping($pings, "passed message");
    pong($pings, $pongs);
    
    echo array_shift($pongs) . "\n";
}

main();

When using arrays as function parameters in PHP, you can specify if an array is meant to be modified by passing it by reference (using &). This specificity increases the type-safety of the program.

The ping function only accepts an array reference for adding values. It would be a logical error to try to remove values from this array within the function.

The pong function accepts two array references, one for receives ($pings) and a second for sends ($pongs).

In the main function, we create two arrays to simulate channels. We then call ping to add a message to $pings, call pong to move the message from $pings to $pongs, and finally print the message from $pongs.

To run the program, save it as channel-directions.php and use the PHP CLI:

$ php channel-directions.php
passed message

This example demonstrates how to simulate channel-like behavior in PHP using arrays and passing them by reference. While it’s not a perfect analogy to channels in concurrent programming, it provides a similar concept of directed communication between functions.