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I have a game with an RPG system where derived stats, like HP,armor, etc depend on a variety of components: armor, stats and feats. I'm running into an issue where the code to change derived metrics gets spread throughout the game - some is in the inventory module, another in stats module, another in buffs module.

How can I centralize and ensure accuracy of all my stat/equipment related changes to the character?

I thought that I can just create a "mega method" within the character class that would recalculate everything any time I change anything within the formula, but I don't know if this recalculate everything is a good practice, or if there are potential pitfalls with this approach down the road.

One of the complications with the complete rebuild that I see is that I will have to keep track of the player's HP and properly restore it after rebuild is complete.

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  • \$\begingroup\$ try delegation, ie the module that gives access to a derived stat registers itself to be notified for any chances relating to specific stats - when any of them change the module updates the derived stat. \$\endgroup\$ – LearnCocos2D Dec 24 '13 at 23:40
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This also largely depends on how your character class is setup.

Assuming we're using direct references here, I would actually refrain from storing your stats directly. Instead I might have the following:

int Player::GetStrength() { return _stats.strength + equipment.GetStrength() + buffs.GetStrength(); }
int Equipment::GetStrength() { return _head.strength + body.strength + gauntlets.strength + leggings.strength + feet.strength }
int Buffs::GetStrength() { int strength = 0; foreach(Buff buff in Buffs) { strength += buff.strength; } return strength; }

Then any time you need to reference this, whether for UI purposes, combat calculations, etc... you have a realtime value with minimal performance cost.

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  • \$\begingroup\$ Great answer, I have an issue where these calls may form long chains - current hp depends on current constitution, which depends on items and speed. Then each monster may call these multiple times. ** Is there a good way to cache these values until an update is needed?** \$\endgroup\$ – Alex Stone Dec 25 '13 at 2:42
  • \$\begingroup\$ Another approach that may work better for you may be to separate these into a Get and Set function for each stat. for example you could have int GetConstitution() { return _stats.constitution; } and void SetConstitution(int value) { _stats.constitution = value; DoUpdateDependents(); } \$\endgroup\$ – Thebluefish Dec 25 '13 at 3:36
  • \$\begingroup\$ @AlexStone: There's many ways to cache them. One simple one is to recalculate a current value only when buffs, equipment, or character level changes. Something like a RecalculateStats method that does all the work and is called when needed. \$\endgroup\$ – Sean Middleditch Dec 25 '13 at 7:16

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