Reducing Cyclomatic Complexity Techniques

TL;DR

Explanation

Cyclomatic complexity (CC) = branches + 1. CC > 10 is complex, > 20 is very complex and untestable. Techniques to reduce: (1) Early returns / guard clauses eliminate nesting, (2) Extract complex conditions to named predicate functions, (3) Replace switch/if chains with lookup tables or strategy pattern, (4) Decompose large functions into smaller ones, (5) Use polymorphism instead of type-checking conditions, (6) Replace nested ternaries with match/switch or named functions. Tools: PHPStan, PHP_CodeSniffer (PHPMD), ESLint (complexity rule), SonarQube.

Common Misconception

Why It Matters

Common Mistakes

• Ignoring CC metrics in code review.
• Reducing CC by moving complexity into long boolean expressions.
• Not using early returns — unnecessary else after return increases nesting.

Code Examples

function process($user, $action) {
    if ($user) {
        if ($user->isActive()) {
            if ($action === 'delete') {
                if ($user->isAdmin()) {
                    // do delete
                } else {
                    throw new Exception('No permission');
                }
            }
        } else {
            throw new Exception('Inactive');
        }
    } else {
        throw new Exception('No user');
    }
}

function process($user, $action) {
    if (!$user) throw new Exception('No user');
    if (!$user->isActive()) throw new Exception('Inactive');
    if ($action === 'delete') deleteUser($user);
}

function deleteUser($user) {
    if (!$user->isAdmin()) throw new Exception('No permission');
    // do delete
}

References

• ↗ https://phpmd.org/rules/complexity.html

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