Track 5 · Tokens · lesson 8

ERC-1155

12 min

A game has 200 item types. Under ERC-721 that is 200 deployed contracts, or one collection where every sword is a distinct token with its own id and no way to say "give me fifty".

ERC-1155 solves both: one contract, many token types, each with quantities.

mapping(uint256 => mapping(address => uint256)) balanceOf;
//      id                  account      amount

One extra mapping level. That is the whole idea.

Multi.solCompose

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One contract, many token types. Build it.

Run the code to see what happens.

Nudge

The only structural change from ERC-20 is one extra mapping level: id first, then account.

Show me the approach

`balanceOf[id][account]`. Mint adds and emits; transfer checks, moves both sides, and emits.

Show me the code

In `transfer`, guard with `if (balanceOf[id][msg.sender] < amount) revert InsufficientBalance();` before touching anything.

Explain the solution

The real ERC-1155 adds batch operations — `safeBatchTransferFrom` moves many ids in one call, which is the standard's actual selling point. A game handing out ten item types pays for one transaction instead of ten.

Fungible and non-fungible in one contract

Because each id has quantities, an id can behave either way:

id 1 = gold coins, supply 1,000,000 → fungible, like ERC-20.
id 2 = the legendary sword, supply 1 → non-fungible, like ERC-721.

Same contract, same functions, same events. The distinction is a choice about supply, not a different standard.

The real selling point is batching. safeBatchTransferFrom moves many ids in a single call.

A game handing a player ten different rewards pays for one transaction rather than ten. At scale that is not a nicety — it is the difference between a playable game and an unplayable one.

Predict

Why does ERC-1155 have no `ownerOf(id)` function?

Because an id can have many holders — there is no single ownerBecause it was left out of the standard by oversightBecause ownership is tracked off-chain

Choosing between the three

| Use case | Standard | |---|---| | A currency or share | ERC-20 | | One unique thing with an identity | ERC-721 | | Many types, some unique, some in quantity | ERC-1155 |

If you would deploy more than a handful of ERC-721 contracts that share a purpose, you probably want ERC-1155 instead.

Check

What is ERC-1155's main practical advantage?

Many token types in one contract, with batch transfersIt is cheaper per individual transferIt supports on-chain metadata and ERC-721 does not

Worth remembering

ERC-1155 indexes balances by id and then by account — one extra mapping level.
The same contract holds fungible and non-fungible ids; supply is what distinguishes them.
Batch transfers are the real advantage — many ids in one transaction.
There is no `ownerOf` because an id can have many holders.
Reach for it when you would otherwise deploy many related ERC-721 contracts.