Arrow functions automatically capture outer variables by value in a concise expression.
What It Does
Arrow functions automatically capture outer variables by value in a concise expression. The following examples distinguish a normal use case, a boundary case and a practical application.
Requirements and Compatibility
PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.
The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.
Example 1: Basic Behavior
Start with the smallest meaningful working case.
<?php
$prices = [18, 29, 42];
print_r(array_map(fn (int $price): int => $price * 2, $prices));Example 2: Another Case
Examine the edge case and the observable result.
<?php
$rate = 0.15;
$totals = array_map(fn (float $price): float => round($price * (1 + $rate), 2), [10.0, 20.0]);
print_r($totals);Practical Example: Putting It to Use
Apply the technique to a small practical task.
<?php
$users = [['active' => true], ['active' => false]];
print_r(array_filter($users, fn (array $user): bool => $user['active']));Important Behavior and Edge Cases
They support one expression, not a full block, and their captured variables are not mutable by reference.
Comparison with Related Functions or Approaches
| Option | What it means in practice |
|---|---|
| Arrow Functions | Arrow functions automatically capture outer variables by value in a concise expression. |
| Related approach | Use a full closure with use (&$variable) when mutable capture is intentional. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Ignoring the important boundary for Arrow Functions | They support one expression, not a full block, and their captured variables are not mutable by reference. |
| Assuming a related mechanism has the same behavior | Use a full closure with use (&$variable) when mutable capture is intentional. |
Key Takeaways
- Arrow functions automatically capture outer variables by value in a concise expression.
- They support one expression, not a full block, and their captured variables are not mutable by reference.
- Use a full closure with use (&$variable) when mutable capture is intentional.
Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.