PHP Proxy Pattern

What It Is

The Proxy pattern puts a stand-in with the same interface in front of a real object. Callers talk to the proxy as if it were the real thing; the proxy decides when and how to involve the original.

Common jobs for a proxy: caching answers, checking access, delaying expensive creation, counting calls.

Example: A Caching Proxy

The real weather service is slow. The proxy answers repeated questions from its cache and only calls the service for new ones — behind the very same interface.

The stand-in that remembers

The first Paris question reaches the remote service; the second is answered from the cache — the "calling the remote service" line prints only once. One isset check on the cache array decides which path a question takes.

Write a PHP script with a caching Proxy: a Weather interface (forecast method), a WeatherService that prints when it calls the remote service, and a CachedWeather proxy that stores answers in an array and serves repeats from cache. Ask for the same city twice and print both answers.

> Output: PHP script

Prompt

Write a PHP script with a caching Proxy: a Weather interface (forecast method), a WeatherService that prints when it calls the remote service, and a CachedWeather proxy that stores answers in an array and serves repeats from cache. Ask for the same city twice and print both answers.

Output: PHP script

<?php

interface Weather {
  public function forecast(string $city): string;
}

// The real service is slow and expensive.
class WeatherService implements Weather {
  public function forecast(string $city): string {
    echo "  (calling the remote service...)\n";
    return "sunny in " . $city;
  }
}

// The proxy stands in front and caches answers.
class CachedWeather implements Weather {
  /** @var array<string, string> */
  private array $cache = [];

  public function __construct(private WeatherService $service) {}

  public function forecast(string $city): string {
    if (isset($this->cache[$city])) {
      return $this->cache[$city] . " (from cache)";
    }
    $answer = $this->service->forecast($city);
    $this->cache[$city] = $answer;
    return $answer;
  }
}

$w = new CachedWeather(new WeatherService());

echo $w->forecast("Paris"), "\n";
echo $w->forecast("Paris"), "\n";

When to Use It

Use it to add caching, access control, laziness or metering in front of something you cannot or should not change — especially remote or expensive resources.

Skip it when you own the object and the behavior belongs inside it. A proxy is for controlling access; a decorator is for adding behavior in layers — pick the intent that matches.

Pros and Cons

Pros: callers need no changes at all; expensive work is skipped or controlled in one place.

Cons: hidden behavior — a caller may get a cached answer without knowing; stale caches and surprise denials are debugged behind an innocent-looking interface.