switch and match

A vending machine doesn't ask "Is it A1? No? Is it A2? No? Is it A3?" You press a code, and it goes straight to the right slot.

In Making Decisions, you chained elseifs. When every condition checks the same variable against different values, PHP offers two tidier tools: the classic switch statement, and the newer match expression (added in PHP 8).

The long way

Here's an elseif chain that turns a day number into a name:

<?php
$day = 3;

if ($day === 1) {
    $name = "Monday";
} elseif ($day === 2) {
    $name = "Tuesday";
} elseif ($day === 3) {
    $name = "Wednesday";
} else {
    $name = "Some other day";
}
echo $name, "\n";

Wednesday

It works, but $day === is repeated on every line. Both switch and match say "look at $day" just once.

switch

<?php
$day = 3;

switch ($day) {
    case 1:
        $name = "Monday";
        break;
    case 2:
        $name = "Tuesday";
        break;
    case 3:
        $name = "Wednesday";
        break;
    default:
        $name = "Some other day";
}
echo $name, "\n";

Wednesday

• switch ($day) names the value to check.
• Each case 1: is a possible value, followed by the code to run.
• break means "done, leave the switch."
• default: runs when no case matched, like a final else.

Forgetting break

break isn't decoration. Without it, PHP keeps going into the next case's code, even though that case doesn't match. That's called fall-through:

<?php
$medal = "silver";

switch ($medal) {
    case "gold":
        echo "First place!\n";
    case "silver":
        echo "Second place!\n";
    case "bronze":
        echo "Third place!\n";
}

Second place!
Third place!

The silver winner is also told they came third. Forgetting break is the most common switch bug.

Fall-through does have one good use: letting several values share the same code, by stacking cases with nothing between them:

<?php
$day = "Sunday";

switch ($day) {
    case "Saturday":
    case "Sunday":
        echo "Weekend!\n";
        break;
    default:
        echo "School day.\n";
}

Weekend!

One more catch: switch compares with loose ==, so the type juggling surprises from Type Juggling and Strict Comparisons apply. A case "1": would match the number 1, too.

match: shorter and stricter

PHP 8 added match. It does the same job, with less typing and fewer traps:

<?php
$day = 3;

$name = match ($day) {
    1 => "Monday",
    2 => "Tuesday",
    3 => "Wednesday",
    default => "Some other day",
};
echo $name, "\n";

Wednesday

How match differs from switch:

• It gives back a value, so you can store it straight into a variable, like $name = match (...). (That's what makes it an expression, not a statement. Notice the ; after the closing brace.)
• No break needed, and no fall-through. Each arm is value => result, and only one arm ever runs.
• It compares strictly, with ===. The number 1 doesn't match the string "1".
• Several values share an arm with commas: "Saturday", "Sunday" => "Weekend!".

When nothing matches

If no arm matches and there's no default, match stops with an error instead of quietly doing nothing:

<?php
$size = "XL";

$price = match ($size) {
    "S" => 150,
    "M" => 180,
    "L" => 200,
};
// error: Uncaught UnhandledMatchError: Unhandled match case 'XL'

That's a feature: a value you forgot about gets noticed right away, instead of causing a hidden bug later. Add a default arm when there really is a sensible fallback.

match with conditions

To choose based on ranges, like grades, use match (true). Each arm is then a condition, and the first one that's true wins:

<?php
$score = 84;

$grade = match (true) {
    $score >= 90 => "A",
    $score >= 80 => "B",
    $score >= 70 => "C",
    default => "Needs improvement",
};
echo "Grade: $grade\n";

Grade: B

Which one to use?

• Choosing a value based on another value: use match. That's most cases.
• Running several lines of code for each case: switch, or if/elseif.
• Checking different variables or complicated conditions: if/elseif.

Try it

A café's order system works out a drink size, a price, and a message. Predict each line.

Running PHP here

Running PHP right in the browser is coming to Syntaxia soon. For now, you can read and edit the code here. If you have PHP installed on your computer (see Setting Up), save it as index.php and run it with php index.php.

Check your prediction

2 medium iced tea: 130 pesos
One for a friend?
Sharing is caring.

"M" gives "medium". In the price match (true), the size isn't large, but the drink is iced tea, so it's 65, and 2 cups make 130. The switch has a missing break in case 2, so it falls through and prints the case 3 line too.

Try it yourself

1. Change $sizeCode to "XL". What's the price now?
2. Change $sizeCode to "XXL". What happens, and how would you fix it?
3. Rewrite the switch as a match that picks the message, and echo the result. What happened to the fall-through?

Check your understanding

What happens in a switch when a case has no break?

The code keeps running into the next case

PHP shows an error

The switch starts again from the top

Nothing, break is optional

What does match do if no arm matches and there's no default?

Returns null

Returns false

Uses the first arm

Throws an UnhandledMatchError

How does match compare values?

Loosely, like ==

Strictly, like ===

Only by type

Alphabetically

Up next

Your code can choose. Next, it'll repeat: counting, going through lists, and running until a job is done, in Loops: for, while, and foreach.