Applying the Strategy Pattern in PHP

The strategy pattern selects interchangeable algorithms behind a small stable interface.

What It Does

The strategy pattern selects interchangeable algorithms behind a small stable interface. 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

Understand the primary operation and its inputs.

<?php
interface PriceRule { public function apply(int $cents): int; }
class TenPercentOff implements PriceRule { public function apply(int $cents): int { return (int) round($cents * 0.9); } }
function total(PriceRule $rule, int $cents): int { return $rule->apply($cents); }
echo total(new TenPercentOff(), 1000);

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
interface Sorting { public function sort(array $items): array; }
class NumericSorting implements Sorting { public function sort(array $items): array { sort($items, SORT_NUMERIC); return $items; } }
print_r((new NumericSorting())->sort([8, 2, 4]));

Practical Example: Putting It to Use

Apply the behavior in a small, controlled scenario.

<?php
interface Shipping { public function fee(int $weight): int; }
class FlatShipping implements Shipping { public function fee(int $weight): int { return 250; } }
function quote(Shipping $method): int { return $method->fee(2); }
echo quote(new FlatShipping());

Important Behavior and Edge Cases

Keep strategies side-effect-aware and injectable so they can be independently tested.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• The strategy pattern selects interchangeable algorithms behind a small stable interface.
• Keep strategies side-effect-aware and injectable so they can be independently tested.
• A decorator adds behavior to one implementation rather than choosing an algorithm.

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