Side Effect Check
Analyze PHP code for side effects that reduce testability.
Side Effect Types
- State mutation — Changing object/array state
- Global access — Reading/writing global variables
- I/O operations — File, network, database
- Output — echo, print, header
- External service calls — API, queue, cache
Detection Patterns
1. State Mutation
// SIDE EFFECT: Mutates input
public function normalize(array &$data): void
{
$data['name'] = trim($data['name']);
$data['email'] = strtolower($data['email']);
}
// PURE: Returns new array
public function normalize(array $data): array
{
return [
'name' => trim($data['name']),
'email' => strtolower($data['email']),
];
}
// SIDE EFFECT: Mutates object
public function complete(Order $order): void
{
$order->setStatus('completed');
$order->setCompletedAt(new DateTime());
}
// BETTER: Command pattern or event
public function complete(Order $order): OrderCompletedEvent
{
return new OrderCompletedEvent($order->getId(), new DateTimeImmutable());
}
2. Global Variable Access
// SIDE EFFECT: Reads global
function getUser(): ?User
{
global $currentUser;
return $currentUser;
}
// SIDE EFFECT: Superglobal access
public function handleRequest(): Response
{
$userId = $_SESSION['user_id']; // Hidden dependency
$data = $_POST; // Hidden input
}
// BETTER: Explicit parameters
public function handleRequest(Session $session, Request $request): Response
{
$userId = $session->get('user_id');
$data = $request->all();
}
3. Static Property Access
// SIDE EFFECT: Static state
class Counter
{
private static int $count = 0;
public static function increment(): void
{
self::$count++; // Shared mutable state
}
public static function getCount(): int
{
return self::$count;
}
}
// BETTER: Instance state
class Counter
{
private int $count = 0;
public function increment(): void
{
$this->count++;
}
}
4. I/O in Business Logic
// SIDE EFFECT: Mixed concerns
public function calculateDiscount(int $userId): float
{
$user = $this->db->query("SELECT * FROM users WHERE id = ?", [$userId]); // I/O
$orderCount = $this->db->query("SELECT COUNT(*) FROM orders WHERE user_id = ?", [$userId]); // I/O
// Pure calculation
if ($orderCount > 100) return 0.20;
if ($orderCount > 50) return 0.15;
return 0.10;
}
// BETTER: Separated concerns
// Pure function
public function calculateDiscountRate(int $orderCount): float
{
return match(true) {
$orderCount > 100 => 0.20,
$orderCount > 50 => 0.15,
default => 0.10,
};
}
// I/O in service
public function getUserDiscountRate(int $userId): float
{
$orderCount = $this->orderRepository->countByUser($userId);
return $this->calculateDiscountRate($orderCount);
}
5. Output Operations
// SIDE EFFECT: Direct output
public function render(array $data): void
{
echo json_encode($data); // Side effect
header('Content-Type: application/json'); // Side effect
}
// BETTER: Return value
public function render(array $data): JsonResponse
{
return new JsonResponse($data);
}
6. Time and Random
// SIDE EFFECT: Non-deterministic
public function createToken(): Token
{
return new Token(
bin2hex(random_bytes(32)), // Random
new DateTime('+1 hour'), // Current time
);
}
// BETTER: Inject dependencies
public function createToken(
RandomGeneratorInterface $random,
ClockInterface $clock,
): Token {
return new Token(
bin2hex($random->bytes(32)),
$clock->now()->modify('+1 hour'),
);
}
7. Logging and Metrics
// SIDE EFFECT: Logging in calculation
public function calculate(Order $order): Money
{
$this->logger->debug('Starting calculation'); // Side effect
$total = $this->computeTotal($order);
$this->metrics->increment('orders.calculated'); // Side effect
$this->logger->info('Calculated', ['total' => $total]); // Side effect
return $total;
}
// BETTER: Separate concerns
public function calculate(Order $order): Money
{
return $this->computeTotal($order);
}
// Decorate for logging
class LoggingOrderCalculator implements OrderCalculatorInterface
{
public function __construct(
private OrderCalculatorInterface $inner,
private LoggerInterface $logger,
) {}
public function calculate(Order $order): Money
{
$this->logger->debug('Starting calculation');
$total = $this->inner->calculate($order);
$this->logger->info('Calculated', ['total' => $total]);
return $total;
}
}
Grep Patterns
# Echo/print
Grep: "(echo|print)\s+" --glob "**/*.php"
# Header calls
Grep: "header\s*\(" --glob "**/*.php"
# Superglobals
Grep: "\$_(GET|POST|SESSION|COOKIE|SERVER|FILES)" --glob "**/*.php"
# Global keyword
Grep: "global\s+\\\$" --glob "**/*.php"
# Static property write
Grep: "(self|static)::\\\$\w+\s*[+\-*\/]?=" --glob "**/*.php"
# File operations
Grep: "(file_put_contents|fwrite|unlink|mkdir|chmod)\(" --glob "**/*.php"
Severity Classification
| Side Effect | Severity |
|---|---|
| Superglobal access | 🟠 Major |
| Static state mutation | 🟠 Major |
| I/O mixed with logic | 🟠 Major |
| Input mutation | 🟡 Minor |
| Logging in pure logic | 🟢 Suggestion |
Refactoring Strategies
Command/Query Separation
// Query: No side effects
public function getTotalPrice(Order $order): Money;
// Command: Side effects
public function completeOrder(Order $order): void;
Return vs Mutate
// Before: Mutate
$order->applyDiscount($discount);
// After: Return new
$discountedOrder = $order->withDiscount($discount);
Output Format
### Side Effect: [Description]
**Severity:** 🟠/🟡/🟢
**Location:** `file.php:line`
**Type:** [State Mutation|Global Access|I/O|...]
**Issue:**
Method mixes business logic with database I/O.
**Current:**
```php
public function calculateDiscount(int $userId): float
{
$user = $this->db->query(...); // I/O
return $this->computeDiscount($user); // Logic
}
Suggested:
public function calculateDiscount(User $user): float
{
return $this->computeDiscount($user); // Pure
}
Testing Impact:
- Before: Need database or complex mocking
- After: Pass User object, test edge cases easily
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