1.2.1125. Simple Switch And Match

Switch() and match() are faster when relying only on literal integers or strings.

Since PHP 7.2, simple switches, that use only literal strings or integers, are optimized. The bigger the switch, the greater the gain. Match() was introduced in PHP 8.0

In particular, this optimisation doesn’t work with any expressions (constant or not), function call, methodcall, constant usage, etc. Only literal values, string or integer.

When the switch is partially build of literals, it is worth splitting the switch in two : first level, only with the literal cases, and, in the default, the dynamic values. This brings some performances, though it is a micro-optimisation.

<?php

// Optimized switch.
switch($b) {
    case "a":
        break;
    case "b":
        break;
    case "c":
        break;
    case "d":
        break;
    default :
        break;
}

// Unoptimized switch.
// Try moving the foo() call in the default, to keep the rest of the switch optimized.
switch($c) {
    case "a":
        break;
    case foo($b):
        break;
    case C:
        break;
    case "c":
        break;
    case "d":
        break;
    default :
        break;
}

// Partially optimised switch
// Try moving the foo() call in the default, to keep the rest of the switch optimized.
switch($c) {
    case "a":
        break;
    case "c":
        break;
    case "d":
        break;
    default :
        switch($c) {
            case foo($b):
            break;

            case C:
            break;

        default :
            break;
        }
        break;
}

?>

See also PHP 7.2’s “switch” optimisations.

1.2.1125.1. Suggestions

• Split the switch between literal and dynamic cases

• Remove the dynamic cases from the switch

• Move the most common case to the beginning of the switch

1.2.1125.2. Specs

Short name	Performances/SimpleSwitch
Rulesets	All, Changed Behavior, Performances
Exakat since	1.0.1
PHP Version	With PHP 7.2 and more recent
Severity	Major
Time To Fix	Quick (30 mins)
Precision	Very high
Features	switch, match
Available in	Entreprise Edition, Exakat Cloud