PHP Strict Types: When and How to Enable Them

Choose strict types to catch accidental scalar coercion and make contracts easier to test.

What It Does

Choose strict types to catch accidental scalar coercion and make contracts easier to test. 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 strict_types declaration applies in the calling file for scalar parameter typing; it does not perform business validation or replace explicit input parsing.

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
declare(strict_types=1);
function units(int $count): int { return $count * 2; }
try { units('3'); } catch (TypeError $e) { echo 'Rejected string at strict call site'; }

Example 2: Another Case

Examine the edge case and the observable result.

<?php
declare(strict_types=1);
function subtotal(float $price): float { return $price * 2; }
echo subtotal(5); // An int can be accepted for float

Practical Example: Putting It to Use

Enable strict mode in each entry file and convert external input explicitly.

<?php
declare(strict_types=1);
function length(string $value): int { return strlen($value); }
try { length(25); } catch (TypeError $e) { echo 'Normalize request input first'; }

Important Behavior and Edge Cases

Explicit normalization remains necessary for form and JSON input.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• Choose strict types to catch accidental scalar coercion and make contracts easier to test.
• Explicit normalization remains necessary for form and JSON input.
• Use declare(strict_types=1) at the beginning of each relevant file.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.