topic Hashable struct for the GS::HashTable<Key, Value> in Archicad C++ API

Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 07:30:38 GMT

Hi,

I need to create a struct that can be used as a Key in a hashtable.

So far I made this:

struct Item{ GS::UInt8 parentId; GS::UInt8 itemId; const GS::UInt8 hash = this->parentId + this->itemId; GS::ULong Item::GenerateHashValue() { return GS::GenerateHashValue(this->hash); } bool operator== (const Item& other) const { return (this->parentId == other.parentId && this->itemId == other.itemId); } };

It gives me the error:

Does not have a GenerateHashValue member or non-member function. I am pretty sure I have GenerateHashValue.

Can you please point some directions on this matter?

Re: Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 08:03:46 GMT

I know how to make it work with c++ standard std::unordered_map

struct Item { int parentId; short itemId; bool operator==(const Item &other) const { return (parentId == other.parentId && itemId == other.itemId); } }; template <> struct std::hash<Item> { std::size_t operator()(const Item& k) const { return (k.itemId + k.parentId); } };

with the above struct I can use the following:

Item itm = { 10, 20 }; Item itm2 = { 10, 20 }; std::unordered_map<Item, int> hashMap; hashMap[itm] = 10; hashMap[itm2] = 30; std::cout << hashMap[itm2] << std::endl;

Output will be 30.

Re: Hashable struct for the GS::HashTable

Oleg — Thu, 14 Oct 2021 10:42:22 GMT

I think you need to mplement the GenerateHashValue as non member function.

GS::ULong GenerateHashValue( const Item& item ) { return GS::GenerateHashValue( item.parentId + item.itemId ); }

Re: Hashable struct for the GS::HashTable

Oleg — Mon, 18 Oct 2021 00:58:14 GMT

And I guess there is other variant.
Inherit your Item from GS::Hashable and implement virtual member
virtual ULong GenerateHashValue (void) const = 0;

like this

struct Item : public GS::Hashable { virtual ULong GenerateHashValue (void) const { return this->hash; } }

Re: Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 13:19:31 GMT

It says it is already declared in the .obj file. GIS is my namespace.

Error LNK2005 "unsigned int __cdecl GIS::GenerateHashValue(struct GIS::Item const &)" (?GenerateHashValue@GIS@@YAIAEBUItem@1@@Z) already defined in AddOnMain.obj AddOn \polyGIS\Build\Source.obj

Re: Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 13:20:06 GMT

I can't find the GS::Hashable class.

Re: Hashable struct for the GS::HashTable

Oleg — Thu, 14 Oct 2021 15:07:31 GMT

Sorry. I worked on old project and checked it for old API.
It seem GS::Hashable was before AC24 and implementation of the HashTable was changed.
I will try it for API 24 and 25 later.

Re: Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 15:11:23 GMT

I was looking at other data structures which work with the GS::hashTable, the GS::Pair<T1, T2>. It has an implementation of the GenerateHashValue() like you said.

//This is from the GS::Pair<> template <class Type1, class Type2> ULong GenerateHashValue (const Pair<Type1, Type2>& pair) { return GS::GenerateHashValue (pair.first, pair.second); }

Re: Hashable struct for the GS::HashTable

Oleg — Thu, 14 Oct 2021 16:57:59 GMT

Fast tests. Works for me. VisualStudio.
Using test is:

GS::HashTable<Item,int> table; Item itm = { 10, 20 }; table.Add(itm, 2); table[itm] = 3;

AC24 (you need const qualifier)

GS::ULong Item::GenerateHashValue() const { return GS::GenerateHashValue(this->hash); }

AC25 (dont have time to study it )

GS::ULong Item::GenerateHashValue() const { return GS::CalculateHashValue(this->hash); }

And just reply. Are you shure to use summary Ids for hashe generation ?
May be beter like this:

GS::ULong Item::GenerateHashValue() const { return ((ULong) parentId << 8 ) | itemId; }

Re: Hashable struct for the GS::HashTable

Mihalcea Bogdan — Thu, 14 Oct 2021 17:02:49 GMT

I was pretty sure that there will be no conflict. Now that I think more about it will not work. Your solution works for me too, I forgot about the const, it is the same behavior as with operator overriding. Thank you very much!