Hey all,

I'm struggling a bit with defining the approach of handling allocation for the mesh instances in my 3d scene class. Some remarks:

• I want to be able to identify them using a unique numeric ID (ideally the vector/array index)
• don't need a full memory pool functionality, because the size in bytes for a single mesh instance object can vary
• looking for a not overcomplex but in balance easy solution, can always improve later on

So far I've come up with 4 different options.
Question; what would you do/ what other options do you see?

Option 1:
Class members:
std::vector<C3dMeshInst> mMeshInstances>
std::vector<uint> mFreeList;

Initial loading:
- reserve(nrMeshInst in scene + some margin)
- load up all initial instances
- add remaining IDs in mFreelist

Add inst:
- Get ID from free list
- Assignment/copy, new mesh inst to free ID

Remove inst:
- 'reset' object in vector, assignment/copy = C3dMeshInst();
- add ID (vector index) to freelist

Option 2:
Class members:
C3dMeshInst *mMeshInstances;
std::vector<uint> mFreeList;

Initial:
- mMeshInstances = new C3dMeshInst(nrMeshInst in scene + some margin)
- load up all initial instances
- add remaining IDs in mFreeList

Add inst:
- Get ID from freelist
- Assignment/copy, new mesh inst to free ID

Remove inst:
- 'reset', by assignment/copy = C3dMeshInst();
- add ID (vector index) to freelist

Option 3:
Class members:
std::vector<C3dMeshInst*> mMeshInstances;
std::vector<uint> mFreeList;

Initial:
- resize mMeshInstances, nrMeshInst in scene + margin
- load up all initial instances, using new C3dMeshInst and assigning pointers in vector

Add inst:
- get vector index from freelist
- 'new' the new mesh inst, assign to pointer in vector

Remove inst:
- 'delete' the mesh inst
- add vector index to mFreeList

Option 4:
see 3, but:
- without freelist
- when removing just move .back() to deleted index
- when adding just push_back new pointer
- downside: ID is no longer guaranteed from vector index (might need ID var in C3dMeshInst class)

Thanks both, I'm going for option 1.
Some answers:

• why? because my current approach does (in this specific case) 5000+ push_back() calls, which I believe is pretty bad practice
  (compared to allocating the vector at once and doing simple assignments: https://www.acodersjourney.com/6-tips-supercharge-cpp-11-vector-performance/
  • I also don't support any form of adding and removing mesh instances
• “And if you have an ID system that can't detect delete+reuse and your not resizing the array, then what is the benefit over a pointer?”
  Well, the vector index == the ID that's used for the mesh instances, so imagine a scene that's created upfront/offline, which contains a number of mesh instances, those all have IDs which I use for several purposes. At some point when I add game objects, I'll have to solve this differently, but for now the vector index is used in a lot of places (also for the renderqueue and spatial subdivision). The benefit over std::vector<object> versus std::vector<object*>, I guess, is that I don't have to new/delete everything manually? (instead, resize the vector just once, allocating all that space in one go)
• the advantage over using std array is that I don't have to keep to a max

Thanks, will read some more into that