Functions · Lesson 8 of 9

Arrow Functions

Use a short arrow function for a single expression.

Lesson

Arrow functions use fn and automatically capture referenced outer variables by value. Their body is one expression, so they are compact callbacks for operations such as mapping a list. Use a regular closure when you need multiple statements or explicit capture behavior. The example maps each number to its doubled value. Further guidance Treat a function as a small contract: name its inputs, state what it returns, and avoid hidden dependencies. Test a representative value and an edge case. Keep a function focused; callers should decide how to display a returned result or handle a reported failure. Practice task: Create a fresh example for Arrow Functions. Predict the result before running it, then change one input and explain why the result changes. Test a normal case and one boundary or invalid case where it applies. Compare your output with the example and note one rule you would use in a real project.

Code examples

Arrow Functions

PHP

$numbers = [1, 2, 3];
$doubled = array_map(fn (int $number): int => $number * 2, $numbers);
echo implode(', ', $doubled);

Expected output

2, 4, 6

Key points

Use a short arrow function for a single expression.
Keep inputs, return values, and side effects explicit.
Prefer focused functions that are easy to test independently.

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