修改集合内对象的可变成员是否安全? [英] Is it safe to modify mutable members of objects inside sets?

问题描述

我对以下情况是否安全感到好奇.

I was curious as to whether the following scenario is safe.

我有以下类定义:

class ActiveStatusEffect
{
public:
    StatusEffect* effect;
    mutable int ReminaingTurns;
    ActiveStatusEffect() : ReminaingTurns(0)
    {
    }
    //Other unimportant stuff down here
}

然后我将其中的一组存储在std :: set中，如下所示:

I then store a group of these inside an std::set as follows:

struct ASECmp
{
    bool operator ()(const StatusEffects::ActiveStatusEffect &eff1, const StatusEffects::ActiveStatusEffect &eff2)
    {
        return eff1.effect->GetPriority() < eff2.effect->GetPriority();
    }
};
std::set<StatusEffects::ActiveStatusEffect, ASECmp> ActiveStatusEffects;

我将RemainingTurns标记为可变的，因为我希望能够更改它而不必不断擦除/插入到集合中.即

I mark RemainingTurns as mutable because I want to be able to change it without haing to constantly erase/insert into the set. I.e.

void BaseCharacter::Tick(Battles::BattleField &field, int ticks)
{
    for (auto effect = ActiveStatusEffects.begin(); effect != ActiveStatusEffects.end();)// ++index)
    {
           auto next = effect;
            ++next;
        if (effect->effect->HasFlag(StatusEffects::STATUS_FLAGS::TickEffect) && effect->ReminaingTurns > 0)
        {                       
            effect->effect->TickCharacter(*this, field, ticks);
            --effect->ReminaingTurns;

        }
        if (effect->ReminaingTurns == 0)
        {
            ActiveStatusEffects.erase(effect);
        }
        effect = next;
    }
}

我很担心，因为这似乎有可能弄乱集合中的顺序，这意味着我不能保证集合将始终按effect-> GetPrority()

I'm concerned because it seems possible for this to mess up the ordering within the set, meaning I can't guarantee the set will always be sorted by effect->GetPrority()

如果是这样，除了复制，修改，擦除然后插入我需要更改的内容之外，是否有安全的方法(例如没有RemainingTurns构成键的一部分)?

If that's true, is there a safe way (such as not have RemainingTurns form part of the key) to do this besides copying, modifying, erasing then inserting what I need to change?

@ildjarn-抱歉，我认为没关系.它只是返回一个存储在StatusEffect中的int值.保证int在程序运行时不会改变.

@ildjarn - sorry, I didn't think that mattered. It just returns an int stored within StatusEffect. That int is guaranteed not to change over the runtime of the program.

int StatusEffect::GetPriority() const
{
    return StatusPriority;
}

推荐答案

更改影响对象顺序的数据确实会破坏关联容器的不变性，但是因为 ActiveStatusEffect :: ReminaingTurns 并非如此涉及到 ActiveStatusEffect 对象的排序，将其保持为 mutable 并修改其值是完全无害的.

Changing data that affects the ordering of an object will indeed break the invariants of associative containers, but because ActiveStatusEffect::ReminaingTurns is not involved in the ordering of ActiveStatusEffect objects whatsoever, keeping it mutable and modifying its value is perfectly harmless.

我很担心，因为这似乎有可能弄乱集合中的顺序，这意味着我不能保证集合将始终按effect-> GetPrority()

I'm concerned because it seems possible for this to mess up the ordering within the set, meaning I can't guarantee the set will always be sorted by effect->GetPrority()

这是 std :: set< StatusEffects :: ActiveStatusEffect，ASECmp> ;除了 ASECmp 定义的标准以外，如何按其他标准进行排序?

It's a std::set<StatusEffects::ActiveStatusEffect, ASECmp>; how could it sort by any criteria other than that defined by ASECmp?

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