PHP's behavior with duplicate keys in associative arrays is by design. When you define an array with the same key multiple times, PHP automatically takes the last occurrence of the key and overwrites the previous value without raising any error or warning.

Why Doesn't PHP Throw an Error for Duplicate Keys?

The main reason PHP doesn't throw an error or warning for duplicate keys is that it's designed to be a forgiving and loosely typed language. This design philosophy prioritizes flexibility and ease of use, allowing developers to work without having to manage strict type or syntax rules, which includes silently handling duplicate keys in arrays.

How Can We Handle Duplicate Keys?

To handle the issue of duplicate keys and catch these scenarios during development, you need to use Static code analysis tools like PHPStan or Psalm can help catch such issues during development. These tools analyze your code and look for potential problems, including duplicate array keys.