ERC-1155: Multi Token Standard
Simple Summary
A standard interface for contracts that manage multiple token types. A single deployed contract may include any combination of fungible tokens, non-fungible tokens or other configurations (e.g. semi-fungible tokens).
Abstract
This standard outlines a smart contract interface that can represent any number of fungible and non-fungible token types. Existing standards such as ERC-20 require deployment of separate contracts per token type. The ERC-721 standard's token ID is a single non-fungible index and the group of these non-fungibles is deployed as a single contract with settings for the entire collection. In contrast, the ERC-1155 Multi Token Standard allows for each token ID to represent a new configurable token type, which may have its own metadata, supply and other attributes.
The _id
argument contained in each function's argument set indicates a specific token or token type in a transaction.
Motivation
Tokens standards like ERC-20 and ERC-721 require a separate contract to be deployed for each token type or collection. This places a lot of redundant bytecode on the Ethereum blockchain and limits certain functionality by the nature of separating each token contract into its own permissioned address. With the rise of blockchain games and platforms like Enjin Coin, game developers may be creating thousands of token types, and a new type of token standard is needed to support them. However, ERC-1155 is not specific to games and many other applications can benefit from this flexibility.
New functionality is possible with this design such as transferring multiple token types at once, saving on transaction costs. Trading (escrow / atomic swaps) of multiple tokens can be built on top of this standard and it removes the need to "approve" individual token contracts separately. It is also easy to describe and mix multiple fungible or non-fungible token types in a single contract.
Specification
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
Smart contracts implementing the ERC-1155 standard MUST implement all of the functions in the ERC1155
interface.
Smart contracts implementing the ERC-1155 standard MUST implement the ERC-165 supportsInterface
function and MUST return the constant value true
if 0xd9b67a26
is passed through the interfaceID
argument.
ERC-1155 Token Receiver
Smart contracts MUST implement all of the functions in the ERC1155TokenReceiver
interface to accept transfers. See "Safe Transfer Rules" for further detail.
Smart contracts MUST implement the ERC-165 supportsInterface
function and signify support for the ERC1155TokenReceiver
interface to accept transfers. See "ERC1155TokenReceiver ERC-165 rules" for further detail.
Safe Transfer Rules
To be more explicit about how the standard safeTransferFrom
and safeBatchTransferFrom
functions MUST operate with respect to the ERC1155TokenReceiver
hook functions, a list of scenarios and rules follows.
Scenarios
Scenario#1 : The recipient is not a contract.
onERC1155Received
andonERC1155BatchReceived
MUST NOT be called on an EOA (Externally Owned Account).
Scenario#2 : The transaction is not a mint/transfer of a token.
onERC1155Received
andonERC1155BatchReceived
MUST NOT be called outside of a mint or transfer process.
Scenario#3 : The receiver does not implement the necessary ERC1155TokenReceiver
interface function(s).
- The transfer MUST be reverted with the one caveat below.
- If the token(s) being sent are part of a hybrid implementation of another standard, that particular standard's rules on sending to a contract MAY now be followed instead. See "Backwards Compatibility" section.
Scenario#4 : The receiver implements the necessary ERC1155TokenReceiver
interface function(s) but returns an unknown value.
- The transfer MUST be reverted.
Scenario#5 : The receiver implements the necessary ERC1155TokenReceiver
interface function(s) but throws an error.
- The transfer MUST be reverted.
Scenario#6 : The receiver implements the ERC1155TokenReceiver
interface and is the recipient of one and only one balance change (e.g. safeTransferFrom
called).
- The balances for the transfer MUST have been updated before the
ERC1155TokenReceiver
hook is called on a recipient contract. - The transfer event MUST have been emitted to reflect the balance changes before the
ERC1155TokenReceiver
hook is called on the recipient contract. - One of
onERC1155Received
oronERC1155BatchReceived
MUST be called on the recipient contract. - The
onERC1155Received
hook SHOULD be called on the recipient contract and its rules followed.- See "onERC1155Received rules" for further rules that MUST be followed.
- The
onERC1155BatchReceived
hook MAY be called on the recipient contract and its rules followed.- See "onERC1155BatchReceived rules" for further rules that MUST be followed.
Scenario#7 : The receiver implements the ERC1155TokenReceiver
interface and is the recipient of more than one balance change (e.g. safeBatchTransferFrom
called).
- All balance transfers that are referenced in a call to an
ERC1155TokenReceiver
hook MUST be updated before theERC1155TokenReceiver
hook is called on the recipient contract. - All transfer events MUST have been emitted to reflect current balance changes before an
ERC1155TokenReceiver
hook is called on the recipient contract. onERC1155Received
oronERC1155BatchReceived
MUST be called on the recipient as many times as necessary such that every balance change for the recipient in the scenario is accounted for.- The return magic value for every hook call MUST be checked and acted upon as per "onERC1155Received rules" and "onERC1155BatchReceived rules".
- The
onERC1155BatchReceived
hook SHOULD be called on the recipient contract and its rules followed.- See "onERC1155BatchReceived rules" for further rules that MUST be followed.
- The
onERC1155Received
hook MAY be called on the recipient contract and its rules followed.- See "onERC1155Received rules" for further rules that MUST be followed.
Scenario#8 : You are the creator of a contract that implements the ERC1155TokenReceiver
interface and you forward the token(s) onto another address in one or both of onERC1155Received
and onERC1155BatchReceived
.
- Forwarding should be considered acceptance and then initiating a new
safeTransferFrom
orsafeBatchTransferFrom
in a new context.- The prescribed keccak256 acceptance value magic for the receiver hook being called MUST be returned after forwarding is successful.
- The
_data
argument MAY be re-purposed for the new context. - If forwarding fails the transaction MAY be reverted.
- If the contract logic wishes to keep the ownership of the token(s) itself in this case it MAY do so.
Scenario#9 : You are transferring tokens via a non-standard API call i.e. an implementation specific API and NOT safeTransferFrom
or safeBatchTransferFrom
.
- In this scenario all balance updates and events output rules are the same as if a standard transfer function had been called.
- i.e. an external viewer MUST still be able to query the balance via a standard function and it MUST be identical to the balance as determined by
TransferSingle
andTransferBatch
events alone.
- i.e. an external viewer MUST still be able to query the balance via a standard function and it MUST be identical to the balance as determined by
- If the receiver is a contract the
ERC1155TokenReceiver
hooks still need to be called on it and the return values respected the same as if a standard transfer function had been called.- However while the
safeTransferFrom
orsafeBatchTransferFrom
functions MUST revert if a receiving contract does not implement theERC1155TokenReceiver
interface, a non-standard function MAY proceed with the transfer. - See "Implementation specific transfer API rules".
- However while the
Rules
safeTransferFrom rules:
- Caller must be approved to manage the tokens being transferred out of the
_from
account (see "Approval" section). - MUST revert if
_to
is the zero address. - MUST revert if balance of holder for token
_id
is lower than the_value
sent to the recipient. - MUST revert on any other error.
- MUST emit the
TransferSingle
event to reflect the balance change (see "TransferSingle and TransferBatch event rules" section). - After the above conditions are met, this function MUST check if
_to
is a smart contract (e.g. code size > 0). If so, it MUST callonERC1155Received
on_to
and act appropriately (see "onERC1155Received rules" section).- The
_data
argument provided by the sender for the transfer MUST be passed with its contents unaltered to theonERC1155Received
hook function via its_data
argument.
- The
safeBatchTransferFrom rules:
- Caller must be approved to manage all the tokens being transferred out of the
_from
account (see "Approval" section). - MUST revert if
_to
is the zero address. - MUST revert if length of
_ids
is not the same as length of_values
. - MUST revert if any of the balance(s) of the holder(s) for token(s) in
_ids
is lower than the respective amount(s) in_values
sent to the recipient. - MUST revert on any other error.
- MUST emit
TransferSingle
orTransferBatch
event(s) such that all the balance changes are reflected (see "TransferSingle and TransferBatch event rules" section). - The balance changes and events MUST occur in the array order they were submitted (_ids[0]/_values[0] before _ids[1]/_values[1], etc).
- After the above conditions are met, this function MUST check if
_to
is a smart contract (e.g. code size > 0). If so, it MUST callonERC1155Received
oronERC1155BatchReceived
on_to
and act appropriately (see "onERC1155Received and onERC1155BatchReceived rules" section).- The
_data
argument provided by the sender for the transfer MUST be passed with its contents unaltered to theERC1155TokenReceiver
hook function(s) via their_data
argument.
- The
TransferSingle and TransferBatch event rules:
TransferSingle
SHOULD be used to indicate a single balance transfer has occurred between a_from
and_to
pair.- It MAY be emitted multiple times to indicate multiple balance changes in the transaction, but note that
TransferBatch
is designed for this to reduce gas consumption. - The
_operator
argument MUST be the address of an account/contract that is approved to make the transfer (SHOULD be msg.sender). - The
_from
argument MUST be the address of the holder whose balance is decreased. - The
_to
argument MUST be the address of the recipient whose balance is increased. - The
_id
argument MUST be the token type being transferred. - The
_value
argument MUST be the number of tokens the holder balance is decreased by and match what the recipient balance is increased by. - When minting/creating tokens, the
_from
argument MUST be set to0x0
(i.e. zero address). See "Minting/creating and burning/destroying rules". - When burning/destroying tokens, the
_to
argument MUST be set to0x0
(i.e. zero address). See "Minting/creating and burning/destroying rules".
- It MAY be emitted multiple times to indicate multiple balance changes in the transaction, but note that
TransferBatch
SHOULD be used to indicate multiple balance transfers have occurred between a_from
and_to
pair.- It MAY be emitted with a single element in the list to indicate a singular balance change in the transaction, but note that
TransferSingle
is designed for this to reduce gas consumption. - The
_operator
argument MUST be the address of an account/contract that is approved to make the transfer (SHOULD be msg.sender). - The
_from
argument MUST be the address of the holder whose balance is decreased for each entry pair in_ids
and_values
. - The
_to
argument MUST be the address of the recipient whose balance is increased for each entry pair in_ids
and_values
. - The
_ids
array argument MUST contain the ids of the tokens being transferred. - The
_values
array argument MUST contain the number of token to be transferred for each corresponding entry in_ids
. _ids
and_values
MUST have the same length.- When minting/creating tokens, the
_from
argument MUST be set to0x0
(i.e. zero address). See "Minting/creating and burning/destroying rules". - When burning/destroying tokens, the
_to
argument MUST be set to0x0
(i.e. zero address). See "Minting/creating and burning/destroying rules".
- It MAY be emitted with a single element in the list to indicate a singular balance change in the transaction, but note that
- The total value transferred from address
0x0
minus the total value transferred to0x0
observed via theTransferSingle
andTransferBatch
events MAY be used by clients and exchanges to determine the "circulating supply" for a given token ID. - To broadcast the existence of a token ID with no initial balance, the contract SHOULD emit the
TransferSingle
event from0x0
to0x0
, with the token creator as_operator
, and a_value
of 0. - All
TransferSingle
andTransferBatch
events MUST be emitted to reflect all the balance changes that have occurred before any call(s) toonERC1155Received
oronERC1155BatchReceived
.- To make sure event order is correct in the case of valid re-entry (e.g. if a receiver contract forwards tokens on receipt) state balance and events balance MUST match before calling an external contract.
onERC1155Received rules:
- The
_operator
argument MUST be the address of an account/contract that is approved to make the transfer (SHOULD be msg.sender).
- The
_from
argument MUST be the address of the holder whose balance is decreased._from
MUST be 0x0 for a mint.
- The
_id
argument MUST be the token type being transferred. - The
_value
argument MUST be the number of tokens the holder balance is decreased by and match what the recipient balance is increased by. - The
_data
argument MUST contain the information provided by the sender for the transfer with its contents unaltered.- i.e. it MUST pass on the unaltered
_data
argument sent via thesafeTransferFrom
orsafeBatchTransferFrom
call for this transfer.
- i.e. it MUST pass on the unaltered
- The recipient contract MAY accept an increase of its balance by returning the acceptance magic value
bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))
- If the return value is
bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))
the transfer MUST be completed or MUST revert if any other conditions are not met for success.
- If the return value is
- The recipient contract MAY reject an increase of its balance by calling revert.
- If the recipient contract throws/reverts the transaction MUST be reverted.
- If the return value is anything other than
bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))
the transaction MUST be reverted. onERC1155Received
(and/oronERC1155BatchReceived
) MAY be called multiple times in a single transaction and the following requirements must be met:- All callbacks represent mutually exclusive balance changes.
- The set of all calls to
onERC1155Received
andonERC1155BatchReceived
describes all balance changes that occurred during the transaction in the order submitted.
- A contract MAY skip calling the
onERC1155Received
hook function if the transfer operation is transferring the token to itself.
onERC1155BatchReceived rules:
- The
_operator
argument MUST be the address of an account/contract that is approved to make the transfer (SHOULD be msg.sender).
- The
_from
argument MUST be the address of the holder whose balance is decreased._from
MUST be 0x0 for a mint.
- The
_ids
argument MUST be the list of tokens being transferred. - The
_values
argument MUST be the list of number of tokens (matching the list and order of tokens specified in_ids
) the holder balance is decreased by and match what the recipient balance is increased by. - The
_data
argument MUST contain the information provided by the sender for the transfer with its contents unaltered.- i.e. it MUST pass on the unaltered
_data
argument sent via thesafeBatchTransferFrom
call for this transfer.
- i.e. it MUST pass on the unaltered
- The recipient contract MAY accept an increase of its balance by returning the acceptance magic value
bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))
- If the return value is
bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))
the transfer MUST be completed or MUST revert if any other conditions are not met for success.
- If the return value is
- The recipient contract MAY reject an increase of its balance by calling revert.
- If the recipient contract throws/reverts the transaction MUST be reverted.
- If the return value is anything other than
bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))
the transaction MUST be reverted. onERC1155BatchReceived
(and/oronERC1155Received
) MAY be called multiple times in a single transaction and the following requirements must be met:- All callbacks represent mutually exclusive balance changes.
- The set of all calls to
onERC1155Received
andonERC1155BatchReceived
describes all balance changes that occurred during the transaction in the order submitted.
- A contract MAY skip calling the
onERC1155BatchReceived
hook function if the transfer operation is transferring the token(s) to itself.
ERC1155TokenReceiver ERC-165 rules:
- The implementation of the ERC-165
supportsInterface
function SHOULD be as follows: - The implementation MAY differ from the above but:
- It MUST return the constant value
true
if0x01ffc9a7
is passed through theinterfaceID
argument. This signifies ERC-165 support. - It MUST return the constant value
true
if0x4e2312e0
is passed through theinterfaceID
argument. This signifies ERC-1155ERC1155TokenReceiver
support. - It MUST NOT consume more than 10,000 gas.
- This keeps it below the ERC-165 requirement of 30,000 gas, reduces the gas reserve needs and minimises possible side-effects of gas exhaustion during the call.
- It MUST return the constant value
Implementation specific transfer API rules:
- If an implementation specific API function is used to transfer ERC-1155 token(s) to a contract, the
safeTransferFrom
orsafeBatchTransferFrom
(as appropriate) rules MUST still be followed if the receiver implements theERC1155TokenReceiver
interface. If it does not the non-standard implementation SHOULD revert but MAY proceed. - An example:
- An approved user calls a function such as
function myTransferFrom(address _from, address _to, uint256[] calldata _ids, uint256[] calldata _values);
. myTransferFrom
updates the balances for_from
and_to
addresses for all_ids
and_values
.myTransferFrom
emitsTransferBatch
with the details of what was transferred from address_from
to address_to
.myTransferFrom
checks if_to
is a contract address and determines that it is so (if not, then the transfer can be considered successful).myTransferFrom
callsonERC1155BatchReceived
on_to
and it reverts or returns an unknown value (if it had returnedbytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))
the transfer can be considered successful).- At this point
myTransferFrom
SHOULD revert the transaction immediately as receipt of the token(s) was not explicitly accepted by theonERC1155BatchReceived
function. - If however
myTransferFrom
wishes to continue it MUST callsupportsInterface(0x4e2312e0)
on_to
and if it returns the constant valuetrue
the transaction MUST be reverted, as it is now known to be a valid receiver and the previous acceptance step failed.- NOTE: You could have called
supportsInterface(0x4e2312e0)
at a previous step if you wanted to gather and act upon that information earlier, such as in a hybrid standards scenario.
- NOTE: You could have called
- If the above call to
supportsInterface(0x4e2312e0)
on_to
reverts or returns a value other than the constant valuetrue
themyTransferFrom
function MAY consider this transfer successful.- NOTE: this MAY result in unrecoverable tokens if sent to an address that does not expect to receive ERC-1155 tokens.
- An approved user calls a function such as
- The above example is not exhaustive but illustrates the major points (and shows that most are shared with
safeTransferFrom
andsafeBatchTransferFrom
):- Balances that are updated MUST have equivalent transfer events emitted.
- A receiver address has to be checked if it is a contract and if so relevant
ERC1155TokenReceiver
hook function(s) have to be called on it. - Balances (and events associated) that are referenced in a call to an
ERC1155TokenReceiver
hook MUST be updated (and emitted) before theERC1155TokenReceiver
hook is called. - The return values of the
ERC1155TokenReceiver
hook functions that are called MUST be respected if they are implemented. - Only non-standard transfer functions MAY allow tokens to be sent to a recipient contract that does NOT implement the necessary
ERC1155TokenReceiver
hook functions.safeTransferFrom
andsafeBatchTransferFrom
MUST revert in that case (unless it is a hybrid standards implementation see "Backwards Compatibility").
Minting/creating and burning/destroying rules:
- A mint/create operation is essentially a specialized transfer and MUST follow these rules:
- To broadcast the existence of a token ID with no initial balance, the contract SHOULD emit the
TransferSingle
event from0x0
to0x0
, with the token creator as_operator
, and a_value
of 0. - The "TransferSingle and TransferBatch event rules" MUST be followed as appropriate for the mint(s) (i.e. singles or batches) however the
_from
argument MUST be set to0x0
(i.e. zero address) to flag the transfer as a mint to contract observers.- NOTE: This includes tokens that are given an initial balance in the contract. The balance of the contract MUST also be able to be determined by events alone meaning initial contract balances (for eg. in construction) MUST emit events to reflect those balances too.
- To broadcast the existence of a token ID with no initial balance, the contract SHOULD emit the
- A burn/destroy operation is essentially a specialized transfer and MUST follow these rules:
- The "TransferSingle and TransferBatch event rules" MUST be followed as appropriate for the burn(s) (i.e. singles or batches) however the
_to
argument MUST be set to0x0
(i.e. zero address) to flag the transfer as a burn to contract observers. - When burning/destroying you do not have to actually transfer to
0x0
(that is impl specific), only the_to
argument in the event MUST be set to0x0
as above.
- The "TransferSingle and TransferBatch event rules" MUST be followed as appropriate for the burn(s) (i.e. singles or batches) however the
- The total value transferred from address
0x0
minus the total value transferred to0x0
observed via theTransferSingle
andTransferBatch
events MAY be used by clients and exchanges to determine the "circulating supply" for a given token ID. - As mentioned above mint/create and burn/destroy operations are specialized transfers and so will likely be accomplished with custom transfer functions rather than
safeTransferFrom
orsafeBatchTransferFrom
. If so the "Implementation specific transfer API rules" section would be appropriate.- Even in a non-safe API and/or hybrid standards case the above event rules MUST still be adhered to when minting/creating or burning/destroying.
- A contract MAY skip calling the
ERC1155TokenReceiver
hook function(s) if the mint operation is transferring the token(s) to itself. In all other cases theERC1155TokenReceiver
rules MUST be followed as appropriate for the implementation (i.e. safe, custom and/or hybrid).
A solidity example of the keccak256 generated constants for the various magic values (these MAY be used by implementation):
Metadata
The URI value allows for ID substitution by clients. If the string {id}
exists in any URI, clients MUST replace this with the actual token ID in hexadecimal form. This allows for a large number of tokens to use the same on-chain string by defining a URI once, for that large number of tokens.
- The string format of the substituted hexadecimal ID MUST be lowercase alphanumeric:
[0-9a-f]
with no 0x prefix. - The string format of the substituted hexadecimal ID MUST be leading zero padded to 64 hex characters length if necessary.
Example of such a URI: https://token-cdn-domain/{id}.json
would be replaced with https://token-cdn-domain/000000000000000000000000000000000000000000000000000000000004cce0.json
if the client is referring to token ID 314592/0x4CCE0.
Metadata Extensions
The optional ERC1155Metadata_URI
extension can be identified with the ERC-165 Standard Interface Detection.
If the optional ERC1155Metadata_URI
extension is included:
- The ERC-165
supportsInterface
function MUST return the constant valuetrue
if0x0e89341c
is passed through theinterfaceID
argument. - Changes to the URI MUST emit the
URI
event if the change can be expressed with an event (i.e. it isn't dynamic/programmatic).- An implementation MAY emit the
URI
event during a mint operation but it is NOT mandatory. An observer MAY fetch the metadata uri at mint time from theuri
function if it was not emitted.
- An implementation MAY emit the
- The
uri
function SHOULD be used to retrieve values if no event was emitted. - The
uri
function MUST return the same value as the latest event for an_id
if it was emitted. - The
uri
function MUST NOT be used to check for the existence of a token as it is possible for an implementation to return a valid string even if the token does not exist.
ERC-1155 Metadata URI JSON Schema
This JSON schema is loosely based on the "ERC721 Metadata JSON Schema", but includes optional formatting to allow for ID substitution by clients. If the string {id}
exists in any JSON value, it MUST be replaced with the actual token ID, by all client software that follows this standard.
- The string format of the substituted hexadecimal ID MUST be lowercase alphanumeric:
[0-9a-f]
with no 0x prefix. - The string format of the substituted hexadecimal ID MUST be leading zero padded to 64 hex characters length if necessary.
An example of an ERC-1155 Metadata JSON file follows. The properties array proposes some SUGGESTED formatting for token-specific display properties and metadata.
Localization
Metadata localization should be standardized to increase presentation uniformity across all languages. As such, a simple overlay method is proposed to enable localization. If the metadata JSON file contains a localization
attribute, its content MAY be used to provide localized values for fields that need it. The localization
attribute should be a sub-object with three attributes: uri
, default
and locales
. If the string {locale}
exists in any URI, it MUST be replaced with the chosen locale by all client software.
JSON Schema
Localized Sample
Base URI:
es.json:
fr.json:
Approval
The function setApprovalForAll
allows an operator to manage one's entire set of tokens on behalf of the approver. To permit approval of a subset of token IDs, an interface such as ERC-1761 Scoped Approval Interface is suggested.
The counterpart isApprovedForAll
provides introspection into any status set by setApprovalForAll
.
An owner SHOULD be assumed to always be able to operate on their own tokens regardless of approval status, so should SHOULD NOT have to call setApprovalForAll
to approve themselves as an operator before they can operate on them.
Rationale
Metadata Choices
The symbol
function (found in the ERC-20 and ERC-721 standards) was not included as we do not believe this is a globally useful piece of data to identify a generic virtual item / asset and are also prone to collisions. Short-hand symbols are used in tickers and currency trading, but they aren't as useful outside of that space.
The name
function (for human-readable asset names, on-chain) was removed from the standard to allow the Metadata JSON to be the definitive asset name and reduce duplication of data. This also allows localization for names, which would otherwise be prohibitively expensive if each language string was stored on-chain, not to mention bloating the standard interface. While this decision may add a small burden on implementers to host a JSON file containing metadata, we believe any serious implementation of ERC-1155 will already utilize JSON Metadata.
Upgrades
The requirement to emit TransferSingle
or TransferBatch
on balance change implies that a valid implementation of ERC-1155 redeploying to a new contract address MUST emit events from the new contract address to replicate the deprecated contract final state. It is valid to only emit a minimal number of events to reflect only the final balance and omit all the transactions that led to that state. The event emit requirement is to ensure that the current state of the contract can always be traced only through events. To alleviate the need to emit events when changing contract address, consider using the proxy pattern, such as described in EIP-2535. This will also have the added benefit of providing a stable contract address for users.
Design decision: Supporting non-batch
The standard supports safeTransferFrom
and onERC1155Received
functions because they are significantly cheaper for single token-type transfers, which is arguably a common use case.
Design decision: Safe transfers only
The standard only supports safe-style transfers, making it possible for receiver contracts to depend on onERC1155Received
or onERC1155BatchReceived
function to be always called at the end of a transfer.
Guaranteed log trace
As the Ethereum ecosystem continues to grow, many dapps are relying on traditional databases and explorer API services to retrieve and categorize data. The ERC-1155 standard guarantees that event logs emitted by the smart contract will provide enough data to create an accurate record of all current token balances. A database or explorer may listen to events and be able to provide indexed and categorized searches of every ERC-1155 token in the contract.
Approval
The function setApprovalForAll
allows an operator to manage one's entire set of tokens on behalf of the approver. It enables frictionless interaction with exchange and trade contracts.
Restricting approval to a certain set of token IDs, quantities or other rules MAY be done with an additional interface or an external contract. The rationale is to keep the ERC-1155 standard as generic as possible for all use-cases without imposing a specific approval scheme on implementations that may not need it. Standard token approval interfaces can be used, such as the suggested ERC-1761 Scoped Approval Interface which is compatible with ERC-1155.
Backwards Compatibility
There have been requirements during the design discussions to have this standard be compatible with existing standards when sending to contract addresses, specifically ERC-721 at time of writing.
To cater for this scenario, there is some leeway with the revert logic should a contract not implement the ERC1155TokenReceiver
as per "Safe Transfer Rules" section above, specifically "Scenario#3 : The receiver does not implement the necessary ERC1155TokenReceiver
interface function(s)".
Hence in a hybrid ERC-1155 contract implementation an extra call MUST be made on the recipient contract and checked before any hook calls to onERC1155Received
or onERC1155BatchReceived
are made.
Order of operation MUST therefore be:
- The implementation MUST call the function
supportsInterface(0x4e2312e0)
on the recipient contract, providing at least 10,000 gas. - If the function call succeeds and the return value is the constant value
true
the implementation proceeds as a regular ERC-1155 implementation, with the call(s) to theonERC1155Received
oronERC1155BatchReceived
hooks and rules associated. - If the function call fails or the return value is NOT the constant value
true
the implementation can assume the recipient contract is not anERC1155TokenReceiver
and follow its other standard's rules for transfers.
Note that a pure implementation of a single standard is recommended rather than a hybrid solution, but an example of a hybrid ERC-1155/ERC-721 contract is linked in the references section under implementations.
An important consideration is that even if the tokens are sent with another standard's rules the ERC-1155 transfer events MUST still be emitted. This is so the balances can still be determined via events alone as per ERC-1155 standard rules.
Usage
This standard can be used to represent multiple token types for an entire domain. Both fungible and non-fungible tokens can be stored in the same smart-contract.
Batch Transfers
The safeBatchTransferFrom
function allows for batch transfers of multiple token IDs and values. The design of ERC-1155 makes batch transfers possible without the need for a wrapper contract, as with existing token standards. This reduces gas costs when more than one token type is included in a batch transfer, as compared to single transfers with multiple transactions.
Another advantage of standardized batch transfers is the ability for a smart contract to respond to the batch transfer in a single operation using onERC1155BatchReceived
.
It is RECOMMENDED that clients and wallets sort the token IDs and associated values (in ascending order) when posting a batch transfer, as some ERC-1155 implementations offer significant gas cost savings when IDs are sorted. See Horizon Games - Multi-Token Standard "packed balance" implementation for an example of this.
Batch Balance
The balanceOfBatch
function allows clients to retrieve balances of multiple owners and token IDs with a single call.
Enumerating from events
In order to keep storage requirements light for contracts implementing ERC-1155, enumeration (discovering the IDs and values of tokens) must be done using event logs. It is RECOMMENDED that clients such as exchanges and blockchain explorers maintain a local database containing the token ID, Supply, and URI at the minimum. This can be built from each TransferSingle, TransferBatch, and URI event, starting from the block the smart contract was deployed until the latest block.
ERC-1155 contracts must therefore carefully emit TransferSingle
or TransferBatch
events in any instance where tokens are created, minted, transferred or destroyed.
Non-Fungible Tokens
The following strategies are examples of how you MAY mix fungible and non-fungible tokens together in the same contract. The standard does NOT mandate how an implementation must do this.
Split ID bits
The top 128 bits of the uint256 _id
parameter in any ERC-1155 function MAY represent the base token ID, while the bottom 128 bits MAY represent the index of the non-fungible to make it unique.
Non-fungible tokens can be interacted with using an index based accessor into the contract/token data set. Therefore to access a particular token set within a mixed data contract and a particular non-fungible within that set, _id
could be passed as <uint128: base token id><uint128: index of non-fungible>
.
To identify a non-fungible set/category as a whole (or a fungible) you COULD just pass in the base id via the _id
argument as <uint128: base token id><uint128: zero>
. If your implementation uses this technique this naturally means the index of a non-fungible SHOULD be 1-based.
Inside the contract code the two pieces of data needed to access the individual non-fungible can be extracted with uint128(~0) and the same mask shifted by 128.
Note that 128 is an arbitrary number, an implementation MAY choose how they would like this split to occur as suitable for their use case. An observer of the contract would simply see events showing balance transfers and mints happening and MAY track the balances using that information alone. For an observer to be able to determine type (non-fungible or fungible) from an ID alone they would have to know the split ID bits format on a implementation by implementation basis.
The ERC-1155 Reference Implementation is an example of the split ID bits strategy.
Natural Non-Fungible tokens
Another simple way to represent non-fungibles is to allow a maximum value of 1 for each non-fungible token. This would naturally mirror the real world, where unique items have a quantity of 1 and fungible items have a quantity greater than 1.
References
Standards
- ERC-721 Non-Fungible Token Standard
- ERC-165 Standard Interface Detection
- ERC-1538 Transparent Contract Standard
- JSON Schema
- RFC 2119 Key words for use in RFCs to Indicate Requirement Levels
Implementations
- ERC-1155 Reference Implementation
- Horizon Games - Multi-Token Standard
- Enjin Coin (GitHub)
- The Sandbox - Dual ERC-1155/721 Contract
Articles & Discussions
- GitHub - Original Discussion Thread
- ERC-1155 - The Crypto Item Standard
- Here Be Dragons - Going Beyond ERC-20 and ERC-721 To Reduce Gas Cost by ~80%
- Blockonomi - Ethereum ERC-1155 Token Perfect for Online Games, Possibly More
- Beyond Gaming - Exploring the Utility of ERC-1155 Token Standard!
- ERC-1155: A new standard for The Sandbox
Copyright
Copyright and related rights waived via CC0.