Delegates and the Observer Pattern

Delegate Performance Impact

How does the performance of delegates compare to direct function calls?

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Delegates do have some performance overhead compared to direct function calls. Let's break down the costs and examine when they matter.

Direct Function Calls

A direct function call is typically compiled into a single CPU instruction:

class Player {
public:
  void TakeDamage(int Damage) {
    UpdateHealthBar(Health - Damage);
  }

private:
  void UpdateHealthBar(int NewHealth) {
    std::cout << "Health: " << NewHealth << '\n';
  }

  int Health{100};
};

Delegate Calls

A delegate using std::function involves:

  • A virtual function call (typically 2-3 instructions)
  • Possible heap allocation during delegate setup
  • Small memory overhead for storing the delegate
class Player {
 public:
  using DamageDelegate = std::function<
    void(int NewHealth)>;

  void SetDelegate(DamageDelegate D) {
    OnDamage = D;  
  }

  void TakeDamage(int Damage) {
    if (OnDamage) OnDamage(Health - Damage);  
  }

 private:
  DamageDelegate OnDamage;
  int Health{100};
};

Performance Impact

For most games, this overhead is negligible. Consider:

  • Modern CPUs execute billions of instructions per second
  • Delegate calls typically happen in response to events (damage, collecting items, etc.) rather than every frame
  • The flexibility benefits often outweigh the small performance cost

However, if you're calling delegates thousands of times per frame, you might want to consider alternatives:

  • Raw function pointers (less overhead but less flexible)
  • Direct virtual function calls
  • Compile-time polymorphism using templates

The key is to profile your specific use case. Don't optimize prematurely - start with the cleaner delegate-based design, and only optimize if profiling shows it's necessary.

Answers to questions are automatically generated and may not have been reviewed.

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