What Is ERC-1155?

ERC-20 requires a separate contract for each token type, and ERC-721 for each collection. In ERC-1155, each token type is identified by an ID number, and the same contract can host many types. If only one unit of a type is minted, it behaves like an NFT; if thousands are minted, it becomes a fungible token like an in-game currency. The standard emerged from a proposal by developers from the Enjin team.

An important feature of the standard is batch operations: many tokens of different types can be transferred or queried in a single transaction, which saves on gas fees. For example, a game can manage a character's unique sword, its many potions and its in-game gold in a single contract and send them to the player in a single transaction. Metadata is generally defined with a single URI template into which the ID number is inserted.

Under the safe transfer rules, a smart contract receiving tokens must implement the standard's receiver interface; otherwise, the transfer is rejected. This rule reduces losses from sending to the wrong contract, but it requires careful coding on the receiving side against reentrancy vulnerabilities.