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Add EIP-223: Token standard with event handling implementation #6485
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--- | ||
eip: 223 | ||
title: 223 Token with communication model | ||
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description: Token with event handling and communication model | ||
author: Dexaran (@Dexaran) | ||
discussions-to: https://ethereum-magicians.org/t/erc-223-token-standard/12894 | ||
status: Draft | ||
type: Standards Track | ||
category: ERC | ||
created: 2017-05-03 | ||
--- | ||
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## Abstract | ||
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The following describes an interface for fungible tokens that supports a `tokenReceived` callback to notify contract recipients when tokens are received. | ||
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## Motivation | ||
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This token introduces a communication model for contracts that can be utilized to straighten the behavior of contracts that interact with such tokens. Specifically, this proposal: | ||
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1. Informs receiving contracts of tokens, as opposed to [ERC-20](./eip-20.md) where the recipient of a token transfer gets no notification. | ||
2. Is more gas-efficient when depositing tokens to contracts. | ||
3. Allows for `_data` recording for financial transfers. | ||
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Generally we recommend using the blurb from the EIP template referring to RFC 2119 to define "MUST", "SHOULD", etc. |
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## Specification | ||
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### Methods | ||
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Contracts intending to receive these tokens MUST implement `tokenReceived`. | ||
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Token transfers to contracts not implementing `tokenReceived` as described below MUST revert. | ||
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### Token contract | ||
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#### `totalSupply` | ||
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```solidity | ||
function totalSupply() view returns (uint256 totalSupply) | ||
``` | ||
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Get the total supply of the token. The functionality of the method is similar to `totalSupply()` of ERC-20. | ||
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#### `name` | ||
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```solidity | ||
function name() view returns (string _name) | ||
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``` | ||
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Get the name of the token. The functionality of the method is similar to `name()` of ERC-20. | ||
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OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present. | ||
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#### `symbol` | ||
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```solidity | ||
function symbol() view returns (bytes32 _symbol) | ||
``` | ||
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Get the symbol of token. The functionality of the method is similar to `symbol()` of ERC-20. | ||
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OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present. | ||
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#### `decimals` | ||
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```solidity | ||
function decimals() view returns (uint8 _decimals) | ||
``` | ||
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Get decimals of token. The functionality of the method is similar to `decimals()` of ERC-20. | ||
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OPTIONAL - This method can be used to improve usability, but interfaces and other contracts MUST NOT expect these values to be present. | ||
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#### `balanceOf` | ||
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```solidity | ||
function balanceOf(address _owner) view returns (uint256 balance) | ||
``` | ||
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Get the account balance of another account with address `_owner`. The functionality of the method is similar to `balanceOf(address)` of ERC-20. | ||
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#### `transfer(address, uint)` | ||
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```solidity | ||
function transfer(address _to, uint _value) returns (bool) | ||
``` | ||
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This function must transfer tokens and invoke the function `tokenReceived(address, uint256, bytes calldata)` in `_to`, if `_to` is a contract. If the `tokenReceived` function is not implemented in `_to` (recipient contract), then the transaction must fail and the transfer of tokens must be reverted. | ||
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If `_to` is an externally owned address, then the transaction must be sent without executing `tokenReceived` in `_to`. | ||
`_data` can be attached to this token transaction and it will stay in blockchain forever (requires more gas). `_data` can be empty. | ||
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#### `transfer(address, uint, bytes)` | ||
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```solidity | ||
function transfer(address _to, uint _value, bytes calldata _data) returns (bool) | ||
``` | ||
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This function must transfer tokens and invoke the function `tokenReceived (address, uint256, bytes)` in `_to`, if `_to` is a contract. If the `tokenReceived` function is not implemented in `_to` (recipient contract), then the transaction must fail and the transfer of tokens must not occur. | ||
If `_to` is an externally owned address, then the transaction must be sent without executing `tokenReceived` in `_to`. | ||
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`_data` can be attached to this token transaction and it will stay in blockchain forever (requires more gas). `_data` can be empty. | ||
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NOTE: A possible way to check whether the `_to` is a contract or an address is to assemble the code of `_to`. If there is no code in `_to`, then this is an externally owned address, otherwise it's a contract. | ||
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### Contract that is intended to receive [ERC-223](./eip-223.md) tokens | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. @SamWilsn have we decided to allow self-references? Also, I feel like we should ignore EIP linking rules for section titles. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. In my opinion allowing self-references in EIPs would improve readability. Imagine that we will have to compare one token (ERC-A) to three others (ERC-B, ERC-C, ERC-D). We need to say that ERC-A is faster than ERC-B, more secure than ERC-C but cuter than ERC-D. At the same time it's cheaper than ERC-B, more expensive than ERC-C and still cuter than ERC-D. With self-referencing: "ERC-A is faster than ERC-B, more secure than ERC-C and cuter than ERC-D. ERC-A is cheaper than ERC-B, ERC-A is more expensive than ERC-C. ERC-A is still cuter than ERC-D." Without self-referencing: "The proposed token is faster than ERC-B, more secure than ERC-C and cuter than ERC-D. This token is cheaper than ERC-B, this token is more expensive than ERC-C. This token is still cuter than ERC-D." Comparisons of ERCs/EIPs would be more readable if ALL EIPs (including the one being proposed) would be in the same format. <disclaimer: English is not my native language so if anything is improperly phrased thats why> There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more.
Self-references would be replaced with "this EIP" or "this ERC." Basically, it means that the reader doesn't need to remember what the current EIP's number is while they read the EIP. So this would become:
Nonetheless, I definitely don't think this rule needs to be applied to section titles, as I feel that "this E[IP/RC]" would be cumbersome there. This comment was just to notify Sam about some eipw changes I would like. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I highly recommend this be at the bottom, below all the events, and that this be a solidity interface to indicate that this is completely separate from the above. |
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```solidity | ||
function tokenReceived(address _from, uint _value, bytes calldata _data) | ||
``` | ||
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A function for handling token transfers, which is called from the token contract, when a token holder sends tokens. `_from` is the address of the sender of the token, `_value` is the amount of incoming tokens, and `_data` is attached data similar to `msg.data` of Ether transactions. It works by analogy with the fallback function of Ether transactions and returns nothing. | ||
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NOTE: `msg.sender` will be a token-contract inside the `tokenReceived` function. It may be important to filter which tokens are sent (by token-contract address). The token sender (the person who initiated the token transaction) will be `_from` inside the `tokenReceived` function. | ||
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IMPORTANT: This function must be named `tokenReceived` and take parameters `address`, `uint256`, `bytes` to match the function signature `0x8943ec02`. | ||
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### Events | ||
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#### `Transfer` | ||
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```solidity | ||
event Transfer(address indexed _from, address indexed _to, uint256 _value) | ||
``` | ||
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Triggered when tokens are transferred. Compatible with ERC-20 `Transfer` event. The functionality of the event is similar to `Transfer` event of ERC-20. | ||
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## Rationale | ||
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This standard introduces a communication model by enforcing the `transfer` to execute a handler function in the destination address. This is an important security consideration as it is required that the receiver explicitly implements the token handling function. In cases where the receiver does not implements such function the transfer MUST be reverted. | ||
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This standard sticks to the push transaction model where the transfer of assets is initiated on the senders side and handled on the receivers side. As the result, ERC-223 transfers are more gas-efficient while dealing with depositing to contracts as ERC-223 tokens can be deposited with just one transaction while ERC-20 tokens require at least two calls (one for `approve` and the second that will invoke `transferFrom`). | ||
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- [ERC-20](./eip-20.md) deposit: `approve` ~53K gas, `transferFrom` ~80K gas | ||
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- ERC-223 deposit: `transfer` and handling on the receivers side ~46K gas | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. How does the deposit + call use less gas than an approve? I feel like this gas usage might be outdated There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I have performed this tests https://github.com/Dexaran/Token_Deposits_GAS_testing using REMIX, solidity 0.8.19, optimization 200 runs Updated the values:
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Your transferFrom function is very unoptimized, with 7 total internal contract calls from the initial |
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This standard introduces the ability to correct user errors by allowing to handle ANY transactions on the recipient side and reject incorrect or improper transactions. This tokens utilize ONE transferring method for both types of interactions with tokens and externally owned addresses which can simplify the user experience and allow to avoid possible user mistakes. | ||
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One downside of the commonly used [ERC-20](./eip-20.md) standard that ERC-223 is intended to solve is that [ERC-20](./eip-20.md) implements two methods of token transferring: (1) `transfer` function and (2) `approve + transferFrom` pattern. Transfer function of [ERC-20](./eip-20.md) standard does not notify the receiver and therefore if any tokens are sent to a contract with the `transfer` function then the receiver will not recognize this transfer and the tokens can become stuck in the receivers address without any possibility of recovering them. | ||
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ERC-223 is intended to simplify the interaction with contracts that are intended to work with tokens. ERC-223 utilizes a "deposit" pattern, similar to that of plain Ether. An ERC-223 deposit to a contract is a simple call of the `transfer` function. This is one transaction as opposed to two step process of `approve + transferFrom` depositing. | ||
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This standard allows payloads to be attached to transactions using the `bytes calldata _data` parameter, which can encode a second function call in the destination address, similar to how `msg.data` does in an Ether transaction, or allow for public logging on chain should it be necessary for financial transactions. | ||
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## Backwards Compatibility | ||
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The interface of this token is similar to that of ERC-20 and most functions serve the same purpose as their analogues in ERC-20. | ||
`transfer(address, uint256, bytes calldata)` function is not backwards compatible with ERC-20 interface. | ||
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ERC-20 tokens can be delivered to a non-contract address with `transfer` function. ERC-20 tokens can be deposited to a contract address with `approve` + `transferFrom` pattern. Depositing ERC-20 tokens to the contract address with `transfer` function will always result in token deposit not being recognized by the recipient contract. | ||
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Here is an example of the contract code that handles ERC-20 token deposit. The following contract can accepts `tokenA` deposits. It is impossible to prevent deposits of tokenA or any other ERC-20 token to this contract that are made with `transfer` function. | ||
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```solidity | ||
contract ERC20Receiver | ||
{ | ||
event Deposit(); | ||
address tokenA; | ||
function deposit(uint _value, address _token) public | ||
{ | ||
require(_token == tokenA); | ||
IERC20(_token).transferFrom(msg.sender, address(this), _value); | ||
emit Deposit(); | ||
} | ||
} | ||
``` | ||
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ERC-223 tokens must be delivered to non-contract address or contract address in the same way with `transfer` function. | ||
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Here is an example of the contract code that handles ERC-223 token deposit. The following contract can filter tokens and only accepts `tokenA`. Other ERC-223 tokens would be rejected. | ||
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```solidity | ||
contract ERC223Receiver | ||
{ | ||
event Deposit(); | ||
address tokenA; | ||
function tokenReceived(address _from, uint _value, bytes memory _data) public | ||
{ | ||
require(msg.sender == tokenA); | ||
emit Deposit(); | ||
} | ||
} | ||
``` | ||
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## Security Considerations | ||
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This token utilizes the model similar to plain Ether behavior. Therefore replay issues must be taken into account. | ||
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### Reference Implementation | ||
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```solidity | ||
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pragma solidity ^0.8.19; | ||
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library Address { | ||
/** | ||
* @dev Returns true if `account` is a contract. | ||
* | ||
* This test is non-exhaustive, and there may be false-negatives: during the | ||
* execution of a contract's constructor, its address will be reported as | ||
* not containing a contract. | ||
* | ||
* > It is unsafe to assume that an address for which this function returns | ||
* false is an externally-owned account (EOA) and not a contract. | ||
*/ | ||
function isContract(address account) internal view returns (bool) { | ||
// This method relies in extcodesize, which returns 0 for contracts in | ||
// construction, since the code is only stored at the end of the | ||
// constructor execution. | ||
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uint256 size; | ||
// solhint-disable-next-line no-inline-assembly | ||
assembly { size := extcodesize(account) } | ||
return size > 0; | ||
} | ||
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/** | ||
* @dev Converts an `address` into `address payable`. Note that this is | ||
* simply a type cast: the actual underlying value is not changed. | ||
*/ | ||
function toPayable(address account) internal pure returns (address payable) { | ||
return payable(account); | ||
} | ||
} | ||
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abstract contract IERC223Recipient { | ||
/** | ||
* @dev Standard ERC223 function that will handle incoming token transfers. | ||
* | ||
* @param _from Token sender address. | ||
* @param _value Amount of tokens. | ||
* @param _data Transaction metadata. | ||
*/ | ||
function tokenReceived(address _from, uint _value, bytes memory _data) public virtual; | ||
} | ||
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/** | ||
* @title Reference implementation of the ERC223 standard token. | ||
*/ | ||
contract ERC223Token { | ||
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/** | ||
* @dev Event that is fired on successful transfer. | ||
*/ | ||
event Transfer(address indexed from, address indexed to, uint value, bytes data); | ||
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string private _name; | ||
string private _symbol; | ||
uint8 private _decimals; | ||
uint256 private _totalSupply; | ||
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mapping(address => uint256) public balances; // List of user balances. | ||
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/** | ||
* @dev Sets the values for {name} and {symbol}, initializes {decimals} with | ||
* a default value of 18. | ||
* | ||
* To select a different value for {decimals}, use {_setupDecimals}. | ||
* | ||
* All three of these values are immutable: they can only be set once during | ||
* construction. | ||
*/ | ||
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constructor(string memory new_name, string memory new_symbol, uint8 new_decimals) | ||
{ | ||
_name = new_name; | ||
_symbol = new_symbol; | ||
_decimals = new_decimals; | ||
} | ||
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/** | ||
* @dev ERC223 tokens must explicitly return "erc223" on standard() function call. | ||
*/ | ||
function standard() public pure returns (string memory) | ||
{ | ||
return "ERC-223"; | ||
} | ||
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/** | ||
* @dev Returns the name of the token. | ||
*/ | ||
function name() public view returns (string memory) | ||
{ | ||
return _name; | ||
} | ||
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/** | ||
* @dev Returns the symbol of the token, usually a shorter version of the | ||
* name. | ||
*/ | ||
function symbol() public view returns (string memory) | ||
{ | ||
return _symbol; | ||
} | ||
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/** | ||
* @dev Returns the number of decimals used to get its user representation. | ||
* For example, if `decimals` equals `2`, a balance of `505` tokens should | ||
* be displayed to a user as `5,05` (`505 / 10 ** 2`). | ||
* | ||
* Tokens usually opt for a value of 18, imitating the relationship between | ||
* Ether and Wei. This is the value {ERC223} uses, unless {_setupDecimals} is | ||
* called. | ||
* | ||
* NOTE: This information is only used for _display_ purposes: it in | ||
* no way affects any of the arithmetic of the contract, including | ||
* {IERC223-balanceOf} and {IERC223-transfer}. | ||
*/ | ||
function decimals() public view returns (uint8) | ||
{ | ||
return _decimals; | ||
} | ||
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/** | ||
* @dev See {IERC223-totalSupply}. | ||
*/ | ||
function totalSupply() public view returns (uint256) | ||
{ | ||
return _totalSupply; | ||
} | ||
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/** | ||
* @dev Returns balance of the `_owner`. | ||
* | ||
* @param _owner The address whose balance will be returned. | ||
* @return balance Balance of the `_owner`. | ||
*/ | ||
function balanceOf(address _owner) public view returns (uint256) | ||
{ | ||
return balances[_owner]; | ||
} | ||
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/** | ||
* @dev Transfer the specified amount of tokens to the specified address. | ||
* Invokes the `tokenFallback` function if the recipient is a contract. | ||
* The token transfer fails if the recipient is a contract | ||
* but does not implement the `tokenFallback` function | ||
* or the fallback function to receive funds. | ||
* | ||
* @param _to Receiver address. | ||
* @param _value Amount of tokens that will be transferred. | ||
* @param _data Transaction metadata. | ||
*/ | ||
function transfer(address _to, uint _value, bytes calldata _data) public returns (bool success) | ||
{ | ||
// Standard function transfer similar to ERC20 transfer with no _data . | ||
// Added due to backwards compatibility reasons . | ||
balances[msg.sender] = balances[msg.sender] - _value; | ||
balances[_to] = balances[_to] + _value; | ||
if(Address.isContract(_to)) { | ||
IERC223Recipient(_to).tokenReceived(msg.sender, _value, _data); | ||
} | ||
emit Transfer(msg.sender, _to, _value, _data); | ||
return true; | ||
} | ||
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/** | ||
* @dev Transfer the specified amount of tokens to the specified address. | ||
* This function works the same with the previous one | ||
* but doesn't contain `_data` param. | ||
* Added due to backwards compatibility reasons. | ||
* | ||
* @param _to Receiver address. | ||
* @param _value Amount of tokens that will be transferred. | ||
*/ | ||
function transfer(address _to, uint _value) public returns (bool success) | ||
{ | ||
bytes memory _empty = hex"00000000"; | ||
balances[msg.sender] = balances[msg.sender] - _value; | ||
balances[_to] = balances[_to] + _value; | ||
if(Address.isContract(_to)) { | ||
IERC223Recipient(_to).tokenReceived(msg.sender, _value, _empty); | ||
} | ||
emit Transfer(msg.sender, _to, _value, _empty); | ||
return true; | ||
} | ||
} | ||
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``` | ||
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## Copyright | ||
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Copyright and related rights waived via [CC0](../LICENSE.md). |
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Note to other editors: this eip is resurrecting #223