Token Standards

[Richa-iitr]

ERC721

• Nonfungible assets: unique and non-divisible, a title of ownership of unique, non-replicable item, one-of-a-kind. Store data rather than value( which is stored in fungible tokens).
• Each NFT has globally unique tokenID and contract address.
• Events: Transfer, Approval, ApproveForAll
• Functions: balanceOf(owner) - returns count of NFTs associated with owner. ownerOf(tokenId) - returns owner of an NFT safeTransferFrom(from,to,tokenId,data) - throws if 'to' address is address[0] transferFrom(from,to,tokenId) - 'from' needs to verify 'to' address is capable of receiving, else NFT lost approve(approved,tokenId) - change or reaffirm approved address, zero address means no one approved. setApprovalForAll(operator, approved) - approve operator to manage assets getApproved(tokenId) - get approved address of tokenId isApprovedForAll(owner,operator) - true if operator is approved for owner.
• Metadata - name(), symblo(), tokenURI()
• Enumeration extension: If application is able to grow then avoid using for/while loops in the code These indicate the contract may be unable to scale and gas costs will rise over time without bound.

Questions

1. Fungible tokens store value as Bitcoin and ERC20 whereas NonFungible Tokens store data. What does data and value refer to here?
2. What does quantity or totalSupply of token denotes? The tokens are unique so how can we have more than one of the same token?
3. Use of data parameter while calling safeTransferFrom? What it actually contains?
4. 'The ERC721 smart contract calls onERC721Received on the recipient after a transfer. This function may throw to revert and reject the transfer. Return of other than the magic value MUST result in the transaction being reverted'. What is the magic value here?

[Richa-iitr]

ERC1155

• Multi Standard Token
• Can transfer multiple token types at once, easy to mix multiple fungible and non-fungible token types in single contract.

[CodeLikeLisa]

Hey Richa - I dm'd you on twitter just looking for a little assistance on some testing on smart contract development I'm currently attempting - would highly appreciate any advice/links/resources to guides that may assist me.