Skip to content

Instantly share code, notes, and snippets.

@gorgos

gorgos/ERC20.sol

Created November 28, 2021 01:18
Show Gist options

  • Select an option

    Learn more about clone URLs
  • Save gorgos/92ecded4a501e329dbf16a66517f1908 to your computer and use it in GitHub Desktop.

Select an option

Learn more about clone URLs
Save gorgos/92ecded4a501e329dbf16a66517f1908 to your computer and use it in GitHub Desktop.
Download ZIP

Revisions

  1. gorgos created this gist Nov 28, 2021.
    388 changes: 388 additions & 0 deletions ERC20.sol
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,388 @@
    // SPDX-License-Identifier: MIT
    pragma solidity ^0.7.0;

    contract ERC20 {
    mapping(address => uint256) private _balances;
    mapping(address => mapping(address => uint256)) private _allowances;
    uint256 private _totalSupply;
    string private _name;
    string private _symbol;

    /**
    * @dev Sets the values for {name} and {symbol}.
    *
    * The default value of {decimals} is 18. To select a different value for
    * {decimals} you should overload it.
    *
    * All two of these values are immutable: they can only be set once during
    * construction.
    */
    constructor(
    string memory name_,
    string memory symbol_,
    uint256 totalSupply_
    ) {
    _name = name_;
    _symbol = symbol_;
    _totalSupply = totalSupply_;

    _balances[_msgSender()] = totalSupply_;
    }

    /**
    * @dev Returns the name of the token.
    */
    function name() public view virtual returns (string memory) {
    return _name;
    }

    /**
    * @dev Returns the symbol of the token, usually a shorter version of the
    * name.
    */
    function symbol() public view virtual returns (string memory) {
    return _symbol;
    }

    /**
    * @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 {ERC20} uses, unless this function is
    * overridden;
    *
    * NOTE: This information is only used for _display_ purposes: it in
    * no way affects any of the arithmetic of the contract, including
    * {IERC20-balanceOf} and {IERC20-transfer}.
    */
    function decimals() public view virtual returns (uint8) {
    return 18;
    }

    /**
    * @dev See {IERC20-totalSupply}.
    */
    function totalSupply() public view virtual returns (uint256) {
    return _totalSupply;
    }

    /**
    * @dev See {IERC20-balanceOf}.
    */
    function balanceOf(address account) public view virtual returns (uint256) {
    return _balances[account];
    }

    /**
    * @dev See {IERC20-transfer}.
    *
    * Requirements:
    *
    * - `recipient` cannot be the zero address.
    * - the caller must have a balance of at least `amount`.
    */
    function transfer(address recipient, uint256 amount)
    public
    virtual
    returns (bool)
    {
    _transfer(_msgSender(), recipient, amount);
    return true;
    }

    /**
    * @dev See {IERC20-allowance}.
    */
    function allowance(address owner, address spender)
    public
    view
    virtual
    returns (uint256)
    {
    return _allowances[owner][spender];
    }

    /**
    * @dev See {IERC20-approve}.
    *
    * Requirements:
    *
    * - `spender` cannot be the zero address.
    */
    function approve(address spender, uint256 amount)
    public
    virtual
    returns (bool)
    {
    _approve(_msgSender(), spender, amount);
    return true;
    }

    /**
    * @dev See {IERC20-transferFrom}.
    *
    * Emits an {Approval} event indicating the updated allowance. This is not
    * required by the EIP. See the note at the beginning of {ERC20}.
    *
    * Requirements:
    *
    * - `sender` and `recipient` cannot be the zero address.
    * - `sender` must have a balance of at least `amount`.
    * - the caller must have allowance for ``sender``'s tokens of at least
    * `amount`.
    */
    function transferFrom(
    address sender,
    address recipient,
    uint256 amount
    ) public virtual returns (bool) {
    _transfer(sender, recipient, amount);

    uint256 currentAllowance = _allowances[sender][_msgSender()];
    require(
    currentAllowance >= amount,
    'ERC20: transfer amount exceeds allowance'
    );
    unchecked {
    _approve(sender, _msgSender(), currentAllowance - amount);
    }

    return true;
    }

    /**
    * @dev Atomically increases the allowance granted to `spender` by the caller.
    *
    * This is an alternative to {approve} that can be used as a mitigation for
    * problems described in {IERC20-approve}.
    *
    * Emits an {Approval} event indicating the updated allowance.
    *
    * Requirements:
    *
    * - `spender` cannot be the zero address.
    */
    function increaseAllowance(address spender, uint256 addedValue)
    public
    virtual
    returns (bool)
    {
    _approve(
    _msgSender(),
    spender,
    _allowances[_msgSender()][spender] + addedValue
    );
    return true;
    }

    /**
    * @dev Atomically decreases the allowance granted to `spender` by the caller.
    *
    * This is an alternative to {approve} that can be used as a mitigation for
    * problems described in {IERC20-approve}.
    *
    * Emits an {Approval} event indicating the updated allowance.
    *
    * Requirements:
    *
    * - `spender` cannot be the zero address.
    * - `spender` must have allowance for the caller of at least
    * `subtractedValue`.
    */
    function decreaseAllowance(address spender, uint256 subtractedValue)
    public
    virtual
    returns (bool)
    {
    uint256 currentAllowance = _allowances[_msgSender()][spender];
    require(
    currentAllowance >= subtractedValue,
    'ERC20: decreased allowance below zero'
    );
    unchecked {
    _approve(_msgSender(), spender, currentAllowance - subtractedValue);
    }

    return true;
    }

    /**
    * @dev Moves `amount` of tokens from `sender` to `recipient`.
    *
    * This internal function is equivalent to {transfer}, and can be used to
    * e.g. implement automatic token fees, slashing mechanisms, etc.
    *
    * Emits a {Transfer} event.
    *
    * Requirements:
    *
    * - `sender` cannot be the zero address.
    * - `recipient` cannot be the zero address.
    * - `sender` must have a balance of at least `amount`.
    */
    function _transfer(
    address sender,
    address recipient,
    uint256 amount
    ) internal virtual {
    require(sender != address(0), 'ERC20: transfer from the zero address');
    require(recipient != address(0), 'ERC20: transfer to the zero address');

    _beforeTokenTransfer(sender, recipient, amount);

    uint256 senderBalance = _balances[sender];
    require(
    senderBalance >= amount,
    'ERC20: transfer amount exceeds balance'
    );
    unchecked {
    _balances[sender] = senderBalance - amount;
    }
    _balances[recipient] += amount;

    emit Transfer(sender, recipient, amount);

    _afterTokenTransfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
    * the total supply.
    *
    * Emits a {Transfer} event with `from` set to the zero address.
    *
    * Requirements:
    *
    * - `account` cannot be the zero address.
    */
    function _mint(address account, uint256 amount) internal virtual {
    require(account != address(0), 'ERC20: mint to the zero address');

    _beforeTokenTransfer(address(0), account, amount);

    _totalSupply += amount;
    _balances[account] += amount;
    emit Transfer(address(0), account, amount);

    _afterTokenTransfer(address(0), account, amount);
    }

    /**
    * @dev Destroys `amount` tokens from `account`, reducing the
    * total supply.
    *
    * Emits a {Transfer} event with `to` set to the zero address.
    *
    * Requirements:
    *
    * - `account` cannot be the zero address.
    * - `account` must have at least `amount` tokens.
    */
    function _burn(address account, uint256 amount) internal virtual {
    require(account != address(0), 'ERC20: burn from the zero address');

    _beforeTokenTransfer(account, address(0), amount);

    uint256 accountBalance = _balances[account];
    require(accountBalance >= amount, 'ERC20: burn amount exceeds balance');
    unchecked {
    _balances[account] = accountBalance - amount;
    }
    _totalSupply -= amount;

    emit Transfer(account, address(0), amount);

    _afterTokenTransfer(account, address(0), amount);
    }

    /**
    * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
    *
    * This internal function is equivalent to `approve`, and can be used to
    * e.g. set automatic allowances for certain subsystems, etc.
    *
    * Emits an {Approval} event.
    *
    * Requirements:
    *
    * - `owner` cannot be the zero address.
    * - `spender` cannot be the zero address.
    */
    function _approve(
    address owner,
    address spender,
    uint256 amount
    ) internal virtual {
    require(owner != address(0), 'ERC20: approve from the zero address');
    require(spender != address(0), 'ERC20: approve to the zero address');

    _allowances[owner][spender] = amount;
    emit Approval(owner, spender, amount);
    }

    /**
    * @dev Hook that is called before any transfer of tokens. This includes
    * minting and burning.
    *
    * Calling conditions:
    *
    * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
    * will be transferred to `to`.
    * - when `from` is zero, `amount` tokens will be minted for `to`.
    * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
    * - `from` and `to` are never both zero.
    *
    * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
    */
    function _beforeTokenTransfer(
    address /*from*/,
    address /*to*/,
    uint256 /*amount*/
    ) internal virtual {}

    /**
    * @dev Hook that is called after any transfer of tokens. This includes
    * minting and burning.
    *
    * Calling conditions:
    *
    * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
    * has been transferred to `to`.
    * - when `from` is zero, `amount` tokens have been minted for `to`.
    * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
    * - `from` and `to` are never both zero.
    *
    * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
    */
    function _afterTokenTransfer(
    address /*from*/,
    address /*to*/,
    uint256 /*amount*/
    ) internal virtual {}

    /**
    *
    */
    function _msgSender() internal view virtual returns (address payable) {
    return msg.sender;
    }

    /**
    * @dev Emitted when `value` tokens are moved from one account (`from`) to
    * another (`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
    );
    }