Delegate Performance Impact

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

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

1class Player {
2public:
3  void TakeDamage(int Damage) {
4    UpdateHealthBar(Health - Damage);
5  }
6
7private:
8  void UpdateHealthBar(int NewHealth) {
9    std::cout << "Health: " << NewHealth << '\n';
10  }
11
12  int Health{100};
13};

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

1class Player {
2 public:
3  using DamageDelegate = std::function<
4    void(int NewHealth)>;
5
6  void SetDelegate(DamageDelegate D) {
7    OnDamage = D;  
8  }
9
10  void TakeDamage(int Damage) {
11    if (OnDamage) OnDamage(Health - Damage);  
12  }
13
14 private:
15  DamageDelegate OnDamage;
16  int Health{100};
17};

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.