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We talked with @elexis about constant references and I gave an example why passing by value may be better than passing by constant reference. During todays refactoring I met another important things that you need to know about constant references. Aliasing Take a look at the following code. Do you see a problem? (It's our code from ps/Shapes.h). // Interface class CSize { public: // ... void operator/=(const float& a); // ... public: float cx, cy; } // Implementation void CSize::operator/=(const float& a) { cx /= a; cy /= a; } If not, would the following usage example help you? CSize size(2560, 1440); // Normalize the size. if (size.cx) size /= size.cx; debug_printf("%f %f", size.cx, size.cy); You'll get: 1.0 1440.0 Because the a references to cx, and the first line of the operator modifies the cx. And in the next we just divide the cy by 1. It may happen in each case where we get the same class. I fixed the problem in D1809. Lifetime Another important thing is a lifetime. Let's take another look at another example (fictional, because I didn't find more detailed example in our code yet): std::vector<Node> nodes; // ... duplicate(nodes[0], 10); // ... void duplicate(const Node& node, size_t times) { for (size_t i = 0; i < times; ++i) nodes.push_back(node); } From first look it seems ok. But, if you know how std::vector works then you know, that on each push_back std::vector can reallocate array to extend it. And then all iterators and raw pointers are invalid, including our constant reference. So after few duplication calls it may contain a trash. So, you need to be careful with such cases.

Hi, I am currently finishing up a project on implementing some emotions in the Petrabot to test a library I've written in C++. However I have run into a problem regarding the data transfer between the Pyrogenesis C++ layer and the mod javascript layer. I apologize for the amount of code in advance, but I am completely stumped as to where the error might be happening. In short, I am trying to convert data contained in a data wrapper class I've made to transfer data from the library. As far as feedback is concerned the data seems to be sent properly without any hiccups as the Javascript end seems to recognize the emotions vector as an object. However, the problem arises when I try to reference the "who" integer as it returns as undefined (this may very well be the case with more of the members of the Emotions wrapper, however I have no evidence that this is the case as of yet). class EmoState { public: class Emotions { public: int who; int strongest; std::vector<const Emote> emotes; Emotions::Emotions(); Emotions::~Emotions(); void SetWho(int s); void SetStrongest(int s); void AddEmotion(const Emote& e); }; int strAt; std::vector<Emotions> emotions; EmoState::EmoState(); EmoState::~EmoState(); void SetStrAt(int s); void AddEmotions(Emotions& e); }; The when the bot requests the data through GetEmoState (below), the C++ architecture fetches the current EmoState (which I've confirmed functions correctly through multiple tests) and tries to convert it for use with the bot. (Though I doubt this script contains the error, I included it to give a complete view of what's happening), static JS::Value GetEmoState(ScriptInterface::CxPrivate* pCxPrivate, int playerid) { ENSURE(pCxPrivate->pCBData); CAIWorker* self = static_cast<CAIWorker*> (pCxPrivate->pCBData); JSContext* cx(self->m_ScriptInterface->GetContext()); JS::RootedValue emoState(cx); const EmoState emoStates = self->ValTest.EmotionalState(playerid); self->m_ScriptInterface->ToJSVal<EmoState>(cx, &emoState, emoStates); return emoState; } The data conversion I wrote to handle the container is as seen below, I suspect that the error lies somewhere in this block of code, however I am not sure what I might have written wrong. template<> void ScriptInterface::ToJSVal<Emote>(JSContext* cx, JS::MutableHandleValue ret, const Emote& val) { JSAutoRequest rq(cx); JS::RootedValue who(cx); JS::RootedValue name(cx); JS::RootedValue intensity(cx); JS::RootedObject obj(cx, JS_NewObject(cx, nullptr, JS::NullPtr(), JS::NullPtr())); if (!obj) { ret.setUndefined(); LOGERROR("Failed to create emote object"); return; } ToJSVal<int>(cx, &who, *val.directedAt); ToJSVal<int>(cx, &name, *val.name); ToJSVal<double>(cx, &intensity, *val.intensity); JS_SetProperty(cx, obj, "directedAt", who); JS_SetProperty(cx, obj, "name", name); JS_SetProperty(cx, obj, "intensity", intensity); ret.setObject(*obj); } template<> void ScriptInterface::ToJSVal<EmoState::Emotions>(JSContext* cx, JS::MutableHandleValue ret, const EmoState::Emotions& val) { JSAutoRequest rq(cx); JS::RootedValue who(cx); JS::RootedValue strongest(cx); JS::RootedObject obj(cx, JS_NewObject(cx, nullptr, JS::NullPtr(), JS::NullPtr())); if (!obj) { ret.setUndefined(); LOGERROR("Failed to create emotions object"); return; } JS::RootedObject em(cx, JS_NewArrayObject(cx, 0)); if (!em) { ret.setUndefined(); LOGERROR("Failed to create emotions object"); return; } for (size_t i = 0; i < val.emotes.size(); ++i) { JS::RootedValue el(cx); ScriptInterface::ToJSVal<Emote>(cx, &el, val.emotes[i]); JS_SetElement(cx, em, i, el); } JS::RootedValue em2(cx); em2.setObject(*em); ToJSVal<int>(cx, &who, val.who); ToJSVal<int>(cx, &strongest, val.strongest); JS_SetProperty(cx, obj, "who", who); JS_SetProperty(cx, obj, "strongest", strongest); JS_SetProperty(cx, obj, "emotes", em2); ret.setObject(*obj); } template<> void ScriptInterface::ToJSVal<EmoState>(JSContext* cx, JS::MutableHandleValue ret, const EmoState& val) { JSAutoRequest rq(cx); JS::RootedObject obj(cx, JS_NewObject(cx, nullptr, JS::NullPtr(), JS::NullPtr())); if (!obj) { ret.setUndefined(); LOGERROR("Failed to create EmoState object"); return; } JS::RootedValue strAt(cx); ScriptInterface::ToJSVal(cx, &strAt, val.strAt); JS::RootedObject em(cx, JS_NewArrayObject(cx, 0)); if (!em) { ret.setUndefined(); LOGERROR("Failed to create EmoState object"); return; } for (size_t i = 0; i < val.emotions.size(); ++i) { JS::RootedValue el(cx); ScriptInterface::ToJSVal<EmoState::Emotions>(cx, &el, val.emotions[i]); JS_SetElement(cx, em, i, el); } JS::RootedValue em2(cx); em2.setObject(*em); JS_SetProperty(cx, obj, "strAt", strAt); JS_SetProperty(cx, obj, "emotions", em2); ret.setObject(*obj); } As mentioned before, the javascript code (as seen below) requests the data, which is then applied to their relevant variables on the javascript end. The specific problem variable in the script is the "eS.who" variable which returns undefined and as such the if statement defaults to else. let emoState = Engine.GetEmoState(PlayerID); let pHF = this.PersonalEmoState.HopeFear; let pJD = this.PersonalEmoState.JoyDistress; let pPS = this.PersonalEmoState.PrideShame; for(let eS in emoState.emotions) { if(eS.who === PlayerID) { this.PersonalEmoState.Strongest = eS.strongest; this.PersonalEmoState.PrideShame = eS.emotes[0].intensity; this.PersonalEmoState.JoyDistress = eS.emotes[1].intensity; this.PersonalEmoState.HopeFear = eS.emotes[2].intensity; this.PersonalEmoState.SatisfactionFearsconfirmed = eS.emotes[3].intensity; this.PersonalEmoState.ReliefDisappointment = eS.emotes[4].intensity; this.PersonalEmoState.GratificationRemorse = eS.emotes[5].intensity; } else { let pGA = m.EmotionHandler.SocialEmoState[eS.who].GratitudeAnger; m.EmotionHandler.SocialEmoState[eS.who].Strongest = eS.strongest; m.EmotionHandler.SocialEmoState[eS.who].AdmirationReproach = eS.emotes[0].intensity; m.EmotionHandler.SocialEmoState[eS.who].HappyforResentment = eS.emotes[1].intensity; m.EmotionHandler.SocialEmoState[eS.who].GloatingPity = eS.emotes[2].intensity; m.EmotionHandler.SocialEmoState[eS.who].GratitudeAnger = eS.emotes[3].intensity; if(gameState.isPlayerAlly(eS.who)) { pJD = (pJD === this.PersonalEmoState.JoyDistress ? 0 : this.PersonalEmoState.JoyDistress); pPS = (pPS === this.PersonalEmoState.PrideShame ? 0 : this.PersonalEmoState.PrideShame); if(pGA !== m.EmotionHandler.SocialEmoState[eS.who].GratitudeAnger) { pGA = m.EmotionHandler.SocialEmoState[eS.who].GratitudeAnger ? 0 : this.PersonalEmoState.PrideShame; this.Config.personality.cooperative = Math.max(Math.min(1, this.Config.personality.cooperative + ((pGA + pPS + pJD)/3)), 0); } } } } this.StrongestAt = emoState.strAt; Once again, I am very sorry for the long post and mass of code. I hope someone will be able to help me as I believe I can make this a cool update. If my tests of the system are successful I am planning on developing a fully Javascript version of my library, which I'll submit as a fork to the Petrabot for people to play with as they want.