Match expression (PHP 8) - Time & Space Complexity

Time Complexity: Match expression (PHP 8)

O(n)

Understanding Time Complexity

Let's see how the time it takes to run a match expression changes as we add more cases.

We want to know how the number of cases affects the work done.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

$value = 3;
switch ($value) {
    case 1:
    case 2:
        $result = 'One or Two';
        break;
    case 3:
        $result = 'Three';
        break;
    default:
        $result = 'Other';
}

// Using match expression
$result = match ($value) {
    1, 2 => 'One or Two',
    3 => 'Three',
    default => 'Other',
};
    

This code uses a match expression to select a result based on the value.

Identify Repeating Operations

Look for repeated checks or comparisons.

• Primary operation: Comparing the input value to each case value.
• How many times: Up to the number of cases, until a match is found.

How Execution Grows With Input

As the number of cases grows, the number of comparisons grows too.

Input Size (n)	Approx. Operations
10	Up to 10 comparisons
100	Up to 100 comparisons
1000	Up to 1000 comparisons

Pattern observation: The work grows roughly in direct proportion to the number of cases.

Final Time Complexity

Time Complexity: O(n)

This means the time to find a match grows linearly with the number of cases.

Common Mistake

[X] Wrong: "Match expressions check all cases at once, so time stays the same no matter how many cases there are."

[OK] Correct: The match expression checks cases one by one until it finds a match, so more cases mean more checks.

Interview Connect

Understanding how match expressions work helps you explain code efficiency clearly and shows you think about how code runs as it grows.

Self-Check

"What if the match expression used a hash map internally to find cases? How would the time complexity change?"

Practice

1. What is the main advantage of using a match expression in PHP 8 compared to a switch statement?

easy

A. It returns a value and uses strict comparison.

B. It allows fall-through between cases.

C. It only works with strings.

D. It requires a default case.

Solution

1. Step 1: Understand match vs switch behavior

   Match expressions return a value directly, unlike switch which is a statement.

2. Step 2: Identify comparison type

   Match uses strict comparison (===), while switch uses loose comparison (==).

3. Final Answer:

   It returns a value and uses strict comparison. -> Option A

4. Quick Check:

   Match returns value + strict check [OK]

Hint: Remember: match returns values and checks types strictly [OK]

Common Mistakes:

• Thinking match allows fall-through like switch
• Believing match works only with strings
• Assuming default case is mandatory in match

2. Which of the following is the correct syntax for a simple match expression in PHP 8?

easy

A. match ($value) { 1 => 'one', 2 => 'two', default => 'other' };

B. match $value { 1: 'one', 2: 'two', default: 'other' };

C. match ($value) { 1: 'one', 2: 'two', default => 'other' };

D. match ($value) { 1 => 'one', 2 => 'two', _ => 'other' };

Solution

1. Step 1: Recall match syntax

   Match uses parentheses around the expression and curly braces with arrows (=>) for cases.

2. Step 2: Identify correct default syntax

   Default case uses the keyword default with =>, not _ or colon.

3. Final Answer:

   match ($value) { 1 => 'one', 2 => 'two', default => 'other' }; -> Option A

4. Quick Check:

   Correct syntax uses parentheses, arrows, and default keyword [OK]

Hint: Use parentheses and arrows => with default keyword [OK]

Common Mistakes:

• Using colon : instead of arrow =>
• Omitting parentheses around the match expression
• Using _ instead of default for fallback

3. What will be the output of the following PHP code?

$status = 2;
$message = match($status) {
    1 => 'Pending',
    2 => 'Approved',
    3 => 'Rejected',
    default => 'Unknown'
};
echo $message;

medium

A. Pending

B. Unknown

C. Rejected

D. Approved

Solution

1. Step 1: Identify the value of $status

   $status is set to 2.

2. Step 2: Match $status to cases

   Case 2 matches 'Approved'.

3. Final Answer:

   Approved -> Option D

4. Quick Check:

   Value 2 matches 'Approved' [OK]

Hint: Match returns the value for exact case match [OK]

Common Mistakes:

• Confusing default case with matched case
• Assuming loose comparison might match wrong case
• Forgetting match returns a value, not prints it

4. Identify the error in this PHP 8 match expression code:

$input = 'banana';
$result = match($input) {
    'apple' => 'fruit',
    'carrot' => 'vegetable'
};
echo $result;

medium

A. Match expression cannot use strings as cases.

B. Syntax error due to missing semicolon after match.

C. Missing default case causes UnhandledMatchError.

D. Variable $result is not assigned properly.

Solution

1. Step 1: Check for default case presence

   The match expression lacks a default case for unmatched values.

2. Step 2: Understand consequences

   If input does not match any case, PHP throws UnhandledMatchError.

3. Final Answer:

   Missing default case causes UnhandledMatchError. -> Option C

4. Quick Check:

   Always include default to avoid errors [OK]

Hint: Always add default case to handle unmatched values [OK]

Common Mistakes:

• Assuming default case is optional
• Thinking strings can't be used as match cases
• Confusing syntax errors with runtime errors

5. You want to categorize a number into 'small', 'medium', or 'large' using a PHP 8 match expression. Which code correctly implements this logic for:
- small: 1 or 2
- medium: 3 or 4
- large: any other number

$num = 3;
// Your match expression here

hard

A. match($num) { 1, 2 => 'small', 3, 4 => 'medium', _ => 'large' };

B. match($num) { 1, 2 => 'small', 3, 4 => 'medium', default => 'large' };

C. match $num { 1, 2 => 'small', 3, 4 => 'medium', default => 'large' };

D. match($num) { 1, 2: 'small', 3, 4: 'medium', default => 'large' };

Solution

1. Step 1: Use comma-separated values for multiple cases

   PHP 8 match allows multiple values per case separated by commas.

2. Step 2: Use correct default keyword

   Default fallback must use default keyword, not underscore or other.

3. Final Answer:

   match($num) { 1, 2 => 'small', 3, 4 => 'medium', default => 'large' }; -> Option B

4. Quick Check:

   Multiple values + default keyword = match($num) { 1, 2 => 'small', 3, 4 => 'medium', default => 'large' }; [OK]

Hint: Use commas for multiple cases and default keyword for fallback [OK]

Common Mistakes:

• Using _ instead of default for fallback
• Not separating multiple cases with commas
• Confusing syntax with switch statement