What is the ERC-1155 multi-token standard?

Why another standard?

ERC-20 and ERC-721 need a separate contract for each token type or collection.¹ The ERC-1155 authors said this puts a lot of repeated code on Ethereum.¹ Blockchain games might need thousands of token types, so the authors wanted a new standard. They add that ERC-1155 is not only for games.¹

ERC-1155 is called the Multi Token Standard. It was created in June 2018, and its official page shows the status Final.¹

Each ID is a token type

In ERC-1155, each token ID stands for its own type of token. Each type can have its own supply and metadata.¹ One contract can mix fungible tokens, non-fungible tokens and other set-ups, such as semi-fungible tokens.¹

Compare this with ERC-721. There, a token ID is one single NFT, and the whole collection shares one contract.¹ In ERC-1155, a type with a supply of just one is in effect an NFT.²

Batches

safeBatchTransferFrom sends several token IDs and amounts in one call.¹ This costs less gas than sending each type in its own transaction.¹

ethereum.org gives an example. Send IDs [3, 6, 13] with amounts [100, 200, 5]. That moves 100 of ID 3, 200 of ID 6 and 5 of ID 13.²

balanceOfBatch works the same way for reading. It gets many balances in a single call.¹ ERC-1155 has no plain transfer function, only transferFrom-style functions. To send your own tokens, you name yourself as the sender.²

Approval is all or nothing

setApprovalForAll lets an operator manage all of your tokens in the contract.¹ You cannot set how many tokens it covers, or which types.² Limiting approval needs something extra, such as another interface or a separate contract.¹

Safer transfers to contracts

The standard transfer functions must fail if the receiving contract lacks the standard's receiving functions.¹ ethereum.org says this means no more tokens stuck in a contract.²

One link for many tokens

A metadata link can contain the text {id}. Apps swap in each token's ID, so one link can serve many tokens.¹ ERC-1155 also leaves out the symbol function. Its authors felt symbols are not very useful outside trading, and different tokens can clash.¹