# Is it possible to use a UClass as a TMap key?

**URL:** <https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728>\
**Category:** C++\
**Tags:** tmap, UClass, unreal-engine, CPP, question\
**Created:** [May 17, 2016, 6:21pm UTC](https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728 "2016-05-17T18:21:45Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![ArcticKiwi](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@ArcticKiwi](https://forums.unrealengine.com/u/ArcticKiwi)\
**Post date:** [May 17, 2016, 6:21pm UTC](https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728/1 "2016-05-17T18:21:45Z")

</div>

Hello !

I find myself with several cases where I want to have a collection of UObject\*, created via a collection of TSubclassOf so that it’s data driven ( using Properties )  
It works well with a TArray.

My issue is that to access an UObject of a particular subclass I need to iterate over the vector, like it’s done for components, and test IsA(). I would prefer an more direct access with a hash map, as accessing an object by class is what i need 90% of the time.

Here is an example of what i’ve tried.

.h

```
TMap<TSubclassOf<class UState>, UState*> StatesMap; ( also tried TMap<UClass*, UState*> )

```

.cpp

```
// creation, object are added to the map at some point
StatesMap.Add(state->GetClass(), state);

// Access
// stateID here is often something like myState::StaticClass()
UState* UStateManager::GetState(const TSubclassOf<class UState>& stateID)
{
	if (StatesMap.Contains(stateID))
	{
		return StatesMap[stateID];
	}
	return nullptr;
}

```

Contains never returns true.  
TSubclassOf has operators to be converted to and from an UClass\*, so i think it’s ok on that front.

I also noticed that if I have a MyState state, then state-\>GetClass() == MyState::StaticClass() always return false which can be the issue.

So what can I change/add to make it work ?

Do I need to override the == operator for UClass\* and the ToHash(UClass\*) method ? ( could not remember the exact name )

Thanks !

AKiwi.

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<div class="post-metadata">

**Author:** ![Daniel\_Hilburn](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Daniel\_Hilburn](https://forums.unrealengine.com/u/Daniel_Hilburn)\
**Post date:** [July 18, 2016, 11:11pm UTC](https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728/2 "2016-07-18T23:11:10Z")

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It looks like you are comparing your MyState class with a MyState subclass, which will fail. I’m actually trying to do the same thing as you, so I don’t yet have the answer. But that is why your comparison is failing.

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**Author:** ![ArcticKiwi](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@ArcticKiwi](https://forums.unrealengine.com/u/ArcticKiwi)\
**Post date:** [July 19, 2016, 1:01pm UTC](https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728/3 "2016-07-19T13:01:13Z")

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Hello !  
Like I said, SubClassOf can automatically be casted as a Class so the test is ok, Contains gets a class as a parameter.

After digging a little more, i noticed that if i create a data object ( blueprint ) inheriting from MyState, then its class object has a name that’s actually generated.

Basically the hierarchy becomes : UState → MyState → MyBlueprintState.

Then I end up comparing a MyDataState Class to a MyState class which returns false, which is ok I guess.

What I really need then is a way to compare a Class to the first c++ class in the hierachy when dealing with blueprinted UObject.

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<div class="post-metadata">

**Author:** ![Daniel\_Hilburn](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Daniel\_Hilburn](https://forums.unrealengine.com/u/Daniel_Hilburn)\
**Post date:** [July 19, 2016, 8:50pm UTC](https://forums.unrealengine.com/t/is-it-possible-to-use-a-uclass-as-a-tmap-key/357728/4 "2016-07-19T20:50:59Z")

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Okay, I got it working for my case, but with caveats.

```
struct FClassMapKey
{
	TWeakObjectPtr<UClass> Class;
	FClassMapKey(const UClass* InClass) : Class(InClass) {}
};
inline bool operator==(const FClassMapKey& KeyA, const FClassMapKey& KeyB)
{
	UClass* ClassA = KeyA.Class.Get();
	UClass* ClassB = KeyB.Class.Get();
	if (ClassA == nullptr)
	{
		return (ClassB != nullptr);
	}
	else if (ClassB == nullptr)
	{
		return false;
	}
	return ClassB->IsChildOf(ClassA);
}
inline uint32 GetTypeHash(const FClassMapKey& Key)
{
	return GetTypeHash(Key.Class);
}

TMap<FClassMapKey, uint32> ClassMap;
ClassMap.FindOrAdd(AActor::StaticClass()) = 0;
uint32* Value = ClassMap.Find(APawn::StaticClass); // returns 0
Value = ClassMap.Find(AActor::StaticClass); // returns 0
Value = ClassMap.Find(UActorComponent::StaticClass); // returns nullptr
ClassMap.FindOrAdd(APawn::StaticClass()) = 5;
Value = ClassMap.Find(APawn::StaticClass); // returns 5
Value = ClassMap.Find(AActor::StaticClass); // returns 5

```

I make a wrapper struct for the UClass\* key which, when compared, will return true for subclasses. This means that if I add the AActor class, I can look it up with AActor or APawn (or any other AActor subclass).

I also got it to work using a custom KeyFuncs subclass of TDefaultMapKeyFuncs as a template parameter to TMap, but this made the TMap declaration terrible. Also, I wanted to store the UClass\* keys as TWeakObjectPtrs, as the TMaps won’t be serialized. This is especially useful if you are storing classes from a module that may be hotloaded or for Blueprint UClasses that may get unloaded out from under you.