What is the pupose of TokenID increment in OpenZepplin implementation?

Question

I am exploring OpenZepplin implementation of ERC721. One thing I found in example of Counters.sol to increment/decrement tokenId. I do get that we do not tokenId for the uniqueness in case the owner holds multiple unique NFTs but why there is a need of increment of it? I assume that each NFT' Token ID is bind to the contract address. Why not just use 1 as a default token Id because that NFT will always be a unique?

Thanks

Answer 1

What makes a token unique within an ERC-721 NFT contract is that token’s tokenId. The ERC-721 NFT standard doesn’t tell you how to assign tokenIds to tokens, but only requires that different tokens have different tokenIds. If a particular NFT contract allows NFTs to be minted one by one, a simple strategy that will guarantee tokenId uniqueness is to assign tokenId = 0 to the first minted token, tokenId = 1 to the second minted token, tokenId = 2 to the next minted token, tokenId = 3 to the next, etc., which is what OpenZeppelin’s ERC721PresetMinterPauserAutoId is doing.

NFT contracts are usually deployed once per collection, so in this case a token’s tokenId needs to identify a token within the entire collection, as described above. However it is possible to use 1 as a “default tokenId” as you have suggested, but only if the NFT contract is deployed once per NFT. This isn’t common practice, because in the long run it could end up consuming a lot of gas, but it’s perfectly doable, and there might be scenarios in which such a strategy is preferable (e.g. if you are going to deploy a single special one-of-a-kind NFT, or if you actually required individual NFTs to have their own Ethereum address). Probably if you opted for this strategy of deploying a “singleton NFT contract” per NFT , you’d want to deploy the NFT implementation once, and then deploy a small proxy for every new NFT that would delegate calls to the common implementation.