Type declarations identify accepted parameter, property and return types.
What It Does
Type declarations identify accepted parameter, property and return types. 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 total(int $quantity, float $price): float { return $quantity * $price; }
echo total(3, 4.5);Example 2: Another Case
Examine the edge case and the observable result.
<?php
function findName(int $id): ?string { return $id === 5 ? 'Rita' : null; }
var_dump(findName(8));Practical Example: Putting It to Use
Function parameter and return declarations make contracts explicit.
<?php
function score(int $wins, int $draws): int { return $wins * 3 + $draws; }
echo score(4, 2);Important Behavior and Edge Cases
They prevent some category errors but do not guarantee business rules such as positive quantities.
Comparison with Related Functions or Approaches
| Option | What it means in practice |
|---|---|
| Type Declarations | Type declarations identify accepted parameter, property and return types. |
| Related approach | Validation and domain objects enforce richer constraints. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Ignoring the important boundary for Type Declarations | They prevent some category errors but do not guarantee business rules such as positive quantities. |
| Assuming a related mechanism has the same behavior | Validation and domain objects enforce richer constraints. |
Key Takeaways
- Type declarations identify accepted parameter, property and return types.
- They prevent some category errors but do not guarantee business rules such as positive quantities.
- Validation and domain objects enforce richer constraints.
Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.