Code examples for http://garrettbluma.com/2012/10/05/exhaustive-pattern-matching-in-php/

figure1.php

<var> = match( <search_term> , <enumerations> ) 
          ->option( <possible_term> , <function> ) 
          ->option( <possible_term> , <function> ) 
          ->option( "_", <function> ) 
          ->exec();

figure2.php

switch ("INIT") { 
    case "INIT": $msg = "program is initializing"; break; 
    case "END": $msg = "program is ending"; break; 
}

figure3.php

$statuses = array("INIT","END"); 
$msg = match("INIT", $statuses) 
       ->option("INIT", function () { return "program is initializing"; } ) 
       ->option("END", function () { return "program is ending"; } ) 
       ->exec();

figure4.php

$statuses = array("INIT","PROCESSING","END");

figure5.php

$msg = match("INIT", $statuses) 
       ->option("INIT", function () { return "program is initializing"; } ) 
       ->option("PROCESSING", function() { return "program is running"; } ) 
       ->option("END", function () { return "program is ending"; } ) 
       ->exec(); 
 
// => No Errors

Matcher.php

<?php 
 
class Matcher {
    private $cases = array(); 
 
    function __construct($target, $source) { 
        $this->target = $target; 
        $this->source = $source; 
    } 
 
    public function option($p,$f) { 
        $this->cases[$p] = $f; 
        return $this; 
    } 
 
    public function exec() { 
        // check that element is in search set 
        if (!isset($this->cases[$this->target])) { 
            // do we have a catch-all? 
            if (isset($this->cases['_'])) { 
                // ... yes, use catch all. 
                return $this->cases["_"](); 
            } else { 
                // ... no, throw error. 
                throw new Exception("Search term not found."); 
            } 
        } 
        if (!isset($this->cases['_'])) { 
            // check for exhaustive matching 
            foreach($this->source as &$s) { 
                if (!isset($this->cases[$s])) { 
                    throw new Exception("$s option not covered" 
                        . " in exhaustive pattern match"); 
                } 
            } 
        }
 
        // we can assume that we have a match return 
        $this->cases[$this->target](); 
    } 
} 
 
// convenience function to simplify implementation 
function match($target, $source) { 
    $o = new Matcher($target, $source); 
    return $o; 
}

usage.php

<?php 
 
// normally we would see something like this. 
switch ("INIT") { 
    case "INIT": $msg = "program is initializing"; break; 
    case "END":  $msg = "program is ending"; break; 
} 
 
/*
 * The problem with this is that we don't know when something is legitimately
 * broken. We assume that any unknown status can be ignored. This is bad.
 */ 
$statuses = array("INIT","END"); 
$msg = match("INIT", $statuses) 
       ->option("INIT", function () { return "program is initializing"; } ) 
       ->option("END", function () { return "program is ending"; } ) 
       ->exec();