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partial pass through ERC20 docs

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Francisco Giordano
2019-05-15 22:13:17 -03:00
parent dd6ec21951
commit 9f6a7e35bd
4 changed files with 142 additions and 57 deletions
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99
contracts/token/ERC20/ERC20.sol
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@ -4,16 +4,27 @@ import "./IERC20.sol";
import "../../math/SafeMath.sol";
/**
* @title Standard ERC20 token
* @dev Implementation of the `IERC20` interface.
*
* @dev Implementation of the basic standard token.
* https://eips.ethereum.org/EIPS/eip-20
* Originally based on code by FirstBlood:
* https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
* This implementation is agnostic to the way tokens are created. This means
* that a supply mechanism has to be added in a derived contract using `_mint`.
* For a generic mechanism see `ERC20Mintable`.
*
* This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
* all accounts just by listening to said events. Note that this isn't required by the specification, and other
* compliant implementations may not do it.
* *For a detailed writeup see our guide [How to implement supply
* mechanisms](https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226).*
*
* We have followed general OpenZeppelin guidelines: functions revert instead
* of returning `false` on failure. This behavior is nonetheless conventional
* and does not conflict with the expectations of ERC20 applications.
*
* Additionally, an `Approval` event is emitted on calls to `transferFrom`.
* This allows applications to reconstruct the allowance for all accounts just
* by listening to said events. Other implementations of the EIP may not emit
* these events, as it isn't required by the specification.
*
* Finally, the non-standard `decreaseAllowance` and `increaseAllowance`
* functions have been added to mitigate the well-known issues around setting
* allowances. See `IERC20.approve`.
*/
contract ERC20 is IERC20 {
using SafeMath for uint256;
@ -25,21 +36,40 @@ contract ERC20 is IERC20 {
uint256 private _totalSupply;
/**
* @dev Total number of tokens in existence.
*/
function totalSupply() public view returns (uint256) {
return _totalSupply;
}
/**
* @dev Gets the balance of the specified address.
* @param owner The address to query the balance of.
* @return A uint256 representing the amount owned by the passed address.
* @dev Returns the amount of tokens owned by an account (`owner`). See `IERC20.balanceOf`.
*/
function balanceOf(address owner) public view returns (uint256) {
return _balances[owner];
}
/**
* @dev Moves tokens from the caller's account to a specified recipient
* (`to`). See `IERC20.transfer`.
*
* Requirements
*
* - `to` cannot be the zero address.
*/
function transfer(address to, uint256 value) public returns (bool) {
_transfer(msg.sender, to, value);
return true;
}
/**
* @dev Configures the amount that a `spender` account is able to spend on
* behalf of the caller. See `IERC20.approve`.
*
* > `approve` can be abused by an untrusted spender.
*
* Requirements
*
* - `spender` cannot be the zero address.
*/
function approve(address spender, uint256 value) public returns (bool) {
_approve(msg.sender, spender, value);
return true;
}
/**
* @dev Function to check the amount of tokens that an owner allowed to a spender.
* @param owner address The address which owns the funds.
@ -50,30 +80,6 @@ contract ERC20 is IERC20 {
return _allowances[owner][spender];
}
/**
* @dev Transfer token to a specified address.
* @param to The address to transfer to.
* @param value The amount to be transferred.
*/
function transfer(address to, uint256 value) public returns (bool) {
_transfer(msg.sender, to, value);
return true;
}
/**
* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
* Beware that changing an allowance with this method brings the risk that someone may use both the old
* and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
* race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
* @param spender The address which will spend the funds.
* @param value The amount of tokens to be spent.
*/
function approve(address spender, uint256 value) public returns (bool) {
_approve(msg.sender, spender, value);
return true;
}
/**
* @dev Transfer tokens from one address to another.
* Note that while this function emits an Approval event, this is not required as per the specification,
@ -118,6 +124,15 @@ contract ERC20 is IERC20 {
return true;
}
/**
* @dev Returns the amount of tokens in existence.
*
* See `IERC20.totalSupply`.
*/
function totalSupply() public view returns (uint256) {
return _totalSupply;
}
/**
* @dev Transfer token for a specified addresses.
* @param from The address to transfer from.

75
contracts/token/ERC20/IERC20.sol
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@ -1,23 +1,78 @@
pragma solidity ^0.5.0;
/**
* @title ERC20 interface
* @dev see https://eips.ethereum.org/EIPS/eip-20
* @dev Interface of the ERC20 standard as defined in the EIP. Does not include
* the optional functions; to access them see [ERC20Detailed](#erc20detailed).
*/
interface IERC20 {
function transfer(address to, uint256 value) external returns (bool);
function approve(address spender, uint256 value) external returns (bool);
function transferFrom(address from, address to, uint256 value) external returns (bool);
function totalSupply() external view returns (uint256);
/**
* @dev Returns the amount of tokens owned by an account (`who`).
*/
function balanceOf(address who) external view returns (uint256);
/**
* @dev Moves tokens from the caller's account to a specified recipient
* (`to`). The amount is specified by `value`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* Emits a `Transfer` event.
*/
function transfer(address to, uint256 value) external returns (bool);
/**
* @dev Configures the amount that a `spender` account is able to spend on
* behalf of the caller. The amount is specified by `value`.
*
* Returns a boolean value indicating whether the operation succeeded.
*
* See `allowance` and `transferFrom`.
*
* > Beware that changing an allowance with this method brings the risk
* that someone may use both the old
* and the new allowance by unfortunate transaction ordering. One possible
* solution to mitigate this race condition is to first reduce the
* spender's allowance to 0 and set the desired value afterwards:
* https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
* Emits an `Approval` event.
*/
function approve(address spender, uint256 value) external returns (bool);
/**
* @dev Returns the current allowance that an `owner` has set for a `spender`.
*
* This value is updated when either `approve` or `transferFrom` are called.
*/
function allowance(address owner, address spender) external view returns (uint256);
/**
* @dev Moves tokens from one account (`from`) to another (`to`). The
* caller must have remaining allowance from the owner (see `approve` and
* `allowance`). If this operation succeeds, the transferred amount
* (`value`) is deducted from the caller's allowance.
*
* Returns a boolean value indicating whether the operation succeeded.
* Emits a `Transfer` event.
*/
function transferFrom(address from, address to, uint256 value) external returns (bool);
/**
* @dev Returns the amount of tokens in existence.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Emitted when tokens are moved from one account (`from`) to anoter (`to`).
*
* Note that `value` may be zero.
*/
event Transfer(address indexed from, address indexed to, uint256 value);
/**
* @dev Emitted when the allowance of a `spender` for an `owner` is set by
* a call to `approve`. `value` is the new allowance.
*/
event Approval(address indexed owner, address indexed spender, uint256 value);
}

23
contracts/token/ERC20/README.md
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@ -1,18 +1,33 @@
---
sections:
- title: Interfaces
- title: Core
contracts:
- IERC20
- title: Contracts
contracts:
- ERC20
- ERC20Detailed
- title: Extensions
contracts:
- ERC20Mintable
- ERC20Burnable
- ERC20Capped
- ERC20Pausable
- ERC20Capped
- title: Utilities
contracts:
- SafeERC20
- TokenTimelock
---
This set of interfaces, contracts, and utilities are all related to the [ERC20 token standard](https://eips.ethereum.org/EIPS/eip-20).
*For a walkthrough on how to create an ERC20 token read our [ERC20 guide](../../learn-about-tokens.md#constructing-a-nice-erc20-token).*
There a few core contracts that implement the behavior specified in the EIP: `IERC20`, `ERC20`, `ERC20Detailed`.
Additionally there are multiple extensions, including:
- designation of addresses that can create token supply (`ERC20Mintable`), with an optional maximum cap (`ERC20Capped`),
- destruction of own tokens (`ERC20Burnable`),
- designation of addresses that can pause token operations for all users (`ERC20Pausable`).
Finally, there are some utilities to interact with ERC20 contracts in various ways.
- `SafeERC20` is a wrapper around the interface that eliminates the need to handle boolean return values.
- `TokenTimelock` can hold tokens for a beneficiary until a specified time.