Match expression (PHP 8) - Step-by-Step Execution

Concept Flow - Match expression (PHP 8)

Evaluate expression

↓

Compare with each case

↓

Match found?

No→Throw error or default

Yes↓

Return matched case value

↓

End

The match expression evaluates a value, compares it to cases, and returns the matching case's result or a default.

Execution Sample

PHP

<?php
$color = 'red';
$result = match($color) {
  'red' => 'Stop',
  'green' => 'Go',
  default => 'Unknown'
};
echo $result;

This code matches the color variable to cases and prints the matching message.

Execution Table

Step	Expression Value	Case Checked	Match?	Action	Output
1	'red'	'red'	Yes	Return 'Stop'
2		'green'	No	Skip
3		default	N/A	Not reached
4				End of match	Stop

💡 Match found at case 'red', returned 'Stop', execution ends.

Variable Tracker

Variable	Start	After match
$color	undefined	'red'
$result	undefined	'Stop'

Key Moments - 2 Insights

Why does the match expression not continue checking other cases after a match?

Because match returns immediately when a case matches, as shown in step 1 of the execution_table where it returns 'Stop' and stops.

What happens if no case matches and there is no default?

Match throws an UnhandledMatchError error. This is not shown here because default is provided.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $result after step 1?

A 'Unknown'

B 'Stop'

C 'Go'

D undefined

💡 Hint

Check the 'Action' and 'Output' columns at step 1 in the execution_table.

At which step does the match expression stop checking cases?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Match?' column and when the action returns a value in the execution_table.

If $color was 'blue' instead of 'red', which case would be matched?

A 'red'

B 'green'

C default

D No match, error thrown

💡 Hint

Refer to the default case in the code and execution_table description.

Concept Snapshot

match(expression) {
  case1 => result1,
  case2 => result2,
  default => defaultResult
};

- Evaluates expression once
- Compares strictly (===) to cases
- Returns matched case value immediately
- Throws error if no match and no default

Full Transcript

The match expression in PHP 8 evaluates a given expression and compares it strictly to each case. When a match is found, it returns the corresponding value immediately and stops checking further cases. If no case matches and a default is provided, it returns the default value. Without a default, it throws an error. This example matches the variable $color to 'red', 'green', or default and returns a message accordingly.