The Hidden Danger of Private Method Calls in Ruby: Why 'send' Can Break Your Code

The Problem

When working with Ruby modules and inheritance, developers often use the sendmethod to call private methods across different classes. While this might seem like a clever workaround, it can lead to subtle bugs and maintenance issues.

The Issue Explained

Consider this common pattern in Ruby applications:

# Base module with private methods
module PaymentProcessor
  private

  def process_payment(amount)
    # Payment logic
    "Processed #{amount}"
  end

  def validate_transaction(user)
    # Validation logic
    user.valid?
  end
end

# Class that includes the module
class PaymentGateway
  include PaymentProcessor

  def handle_payment(amount, user)
    # Using send to call private methods
    result = send(:process_payment, amount)
    valid = send(:validate_transaction, user)

    return result if valid
  end
end

Why This Breaks

The send method bypasses Ruby's method visibility rules, which can cause several problems:

1. Method Signature Changes: If the private method's signature changes, the sendcall won't be caught by the compiler

2. Refactoring Nightmares: IDEs and static analysis tools can't properly track these calls

3. Debugging Difficulties: Stack traces become confusing when methods are called via send

4. Testing Complexity: It's harder to mock or stub methods called via send

The Solution

Instead of using send, make the methods public or use proper delegation:

# Better approach: Make methods public
module PaymentProcessor
  def process_payment(amount)
    # Payment logic
    "Processed #{amount}"
  end

  def validate_transaction(user)
    # Validation logic
    user.valid?
  end
end

# Clean, readable code
class PaymentGateway
  include PaymentProcessor

  def handle_payment(amount, user)
    # Direct method calls - much cleaner!
    result = process_payment(amount)
    valid = validate_transaction(user)

    return result if valid
  end
end

Alternative: Proper Delegation

If you need to maintain encapsulation, use proper delegation patterns:

class PaymentGateway
  include PaymentProcessor

  def handle_payment(amount, user)
    # Delegate to a dedicated processor
    PaymentHandler.new.process(amount, user)
  end
end

class PaymentHandler
  def process(amount, user)
    result = process_payment(amount)
    valid = validate_transaction(user)

    return result if valid
  end

  private

  def process_payment(amount)
    "Processed #{amount}"
  end

  def validate_transaction(user)
    user.valid?
  end
end

Key Takeaways

1. Avoid send for method calls: It breaks encapsulation and makes code harder to maintain

2. Make methods public when appropriate: Don't hide methods that need to be called from other classes

3. Use proper delegation: Create dedicated classes or modules for shared functionality

4. Follow Ruby conventions: Let the language's visibility rules work for us, not against us

Real-World Impact

In production applications, send calls can lead to:

• Runtime errors that are hard to debug

• Performance issues due to method lookup overhead

• Code that's difficult to refactor or test

• Maintenance headaches for future developers

The fix is simple: replace send calls with direct method calls and adjust method visibility accordingly.