Union type declarations allow a value to match any of several declared alternatives.
What It Does
Union type declarations allow a value to match any of several declared alternatives. 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 renderId(int|string $id): string { return (string) $id; }
echo renderId('A42');Example 2: Another Case
Examine the edge case and the observable result.
<?php
function parseValue(float|int $value): float { return $value * 1.2; }
echo parseValue(10);Practical Example: Putting It to Use
Apply the technique to a small practical task.
<?php
function find(int|string $key): array|null { return $key === 0 ? null : ['key' => $key]; }
print_r(find(7));Important Behavior and Edge Cases
Union types still require careful input normalization; they do not validate semantic meaning.
Comparison with Related Functions or Approaches
| Option | What it means in practice |
|---|---|
| Union Types Explained with Examples | Union type declarations allow a value to match any of several declared alternatives. |
| Related approach | Intersection types require every interface at once rather than any one type. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Ignoring the important boundary for Union Types Explained with Examples | Union types still require careful input normalization; they do not validate semantic meaning. |
| Assuming a related mechanism has the same behavior | Intersection types require every interface at once rather than any one type. |
Key Takeaways
- Union type declarations allow a value to match any of several declared alternatives.
- Union types still require careful input normalization; they do not validate semantic meaning.
- Intersection types require every interface at once rather than any one type.
Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.