How To Use TMap?

Development Programming & Scripting C++
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1

TMap is exactly what I need considering it works similar to the stl::map. The issue is that it seemes to work a bit differently. I get that it sorts based on hashes. What do I need to implement for my custom struct to be used as a key? The documentation is less than helpful. TMap | Unreal Engine Documentation

2

Here you go:

TMap<struct FBoneIndexPair, TArray<uint32> > VertexInfluenceMapping;


/** 
* A pair of bone indices
*/
struct FBoneIndexPair
{
	int32 BoneIdx[2];

	bool operator==(const FBoneIndexPair& Src) const
	{
		return (BoneIdx[0] == Src.BoneIdx[0]) && (BoneIdx[1] == Src.BoneIdx[1]);
	}

	friend FORCEINLINE uint32 GetTypeHash( const FBoneIndexPair& BonePair )
	{
		return FCrc::MemCrc_DEPRECATED(&BonePair, sizeof(FBoneIndexPair));
	}

	/**
	* Serialize to Archive
	*/
	friend FArchive& operator<<( FArchive& Ar, FBoneIndexPair& W )
	{
		return Ar << W.BoneIdx[0] << W.BoneIdx[1];
	}
};

I think the most important part of this struct is == operator.

3

You are correct! I did not have the == operator implemented correctly.

4

Exactly what I needed! Made a version based on Cantor pairs without the deprecated cyclic redundancy thing. Perhaps a tiny bit less performant, but should work well for bounded indices like the ones above:

	friend FORCEINLINE uint32 GetTypeHash(const IndexPair& indexPair)
	{
		return (indexPair.key + indexPair.value) * (indexPair.key + indexPair.value + 1) / 2 + indexPair.value;
	}