Glossary

Strategy Pattern

Strategy is a pattern that extracts a varying behaviour into a separate class (the strategy) and allows it to be swapped at runtime. The class depends on the strategy interface, not on a concrete implementation.

Example

interface SortStrategy {
  sort(array $data): array;
}
class QuickSort implements SortStrategy { ... }
class MergeSort implements SortStrategy { ... }

class Sorter {
  public function __construct(private SortStrategy $strategy) {}
  public function sort(array $data): array {
    return $this->strategy->sort($data);
  }
}

When to use

There are multiple variants of an algorithm and you need to switch between them
You want to avoid large if/switch blocks selecting the algorithm
The behaviour should be configurable from outside or changeable at runtime