Default function arguments apply when the caller omits an argument, not whenever a null value is supplied.
What It Does
Default function arguments apply when the caller omits an argument, not whenever a null value is supplied. 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
function greeting(string $name = 'Guest'): string { return 'Hi, ' . $name; }
echo greeting();Example 2: Another Case
Examine the edge case and the observable result.
<?php
function rangeTotal(int $start, int $length = 3): int { return array_sum(range($start, $start + $length - 1)); }
echo rangeTotal(2);Practical Example: Putting It to Use
Apply the technique to a small practical task.
<?php
function translate(string $word, string $lang = 'en'): string { return $lang . ':' . $word; }
echo translate('hello', lang: 'fr');Important Behavior and Edge Cases
Avoid mutable shared default objects; use explicit nullable defaults when null is valid.
Comparison with Related Functions or Approaches
| Option | What it means in practice |
|---|---|
| Default Function Arguments | Default function arguments apply when the caller omits an argument, not whenever a null value is supplied. |
| Related approach | Named arguments let callers specify optional values by name. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Ignoring the important boundary for Default Function Arguments | Avoid mutable shared default objects; use explicit nullable defaults when null is valid. |
| Assuming a related mechanism has the same behavior | Named arguments let callers specify optional values by name. |
Key Takeaways
- Default function arguments apply when the caller omits an argument, not whenever a null value is supplied.
- Avoid mutable shared default objects; use explicit nullable defaults when null is valid.
- Named arguments let callers specify optional values by name.
Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.