ERC functionality split into internal/external

src/ERC20External.sol

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.30;
+
+import {IERC20Errors} from "../lib/openzeppelin-contracts/contracts/interfaces/draft-IERC6093.sol";
+import {IERC20} from "../lib/openzeppelin-contracts/contracts/token/ERC20/IERC20.sol";
+import {Context} from "../lib/openzeppelin-contracts/contracts/utils/Context.sol";
+import {IERC20Metadata} from "../lib/openzeppelin-contracts/contracts/token/ERC20/extensions/IERC20Metadata.sol";
+import {ERC20Internal} from "./ERC20Internal.sol";
+
+// Copied from OpenZeppelin's ERC20 implementation, but split into internal and external parts
+
+contract ERC20External is ERC20Internal, IERC20Metadata {
+    /**
+     * @dev Sets the values for {name} and {symbol}.
+     *
+     * Both values are immutable: they can only be set once during construction.
+     */
+    constructor(string memory name_, string memory symbol_) {
+        _name = name_;
+        _symbol = symbol_;
+    }
+
+
+    /**
+     * @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 default value returned by this function, unless
+     * it's 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;
+    }
+
+    /// @inheritdoc IERC20
+    function totalSupply() public view virtual returns (uint256) {
+        return _totalSupply;
+    }
+
+    /// @inheritdoc IERC20
+    function balanceOf(address account) public view virtual returns (uint256) {
+        return _balances[account];
+    }
+
+    /**
+     * @dev See {IERC20-transfer}.
+     *
+     * Requirements:
+     *
+     * - `to` cannot be the zero address.
+     * - the caller must have a balance of at least `value`.
+     */
+    function transfer(address to, uint256 value) public virtual returns (bool) {
+        address owner = _msgSender();
+        _transfer(owner, to, value);
+        return true;
+    }
+
+    /// @inheritdoc IERC20
+    function allowance(address owner, address spender) public view virtual returns (uint256) {
+        return _allowances[owner][spender];
+    }
+
+    /**
+     * @dev See {IERC20-approve}.
+     *
+     * NOTE: If `value` is the maximum `uint256`, the allowance is not updated on
+     * `transferFrom`. This is semantically equivalent to an infinite approval.
+     *
+     * Requirements:
+     *
+     * - `spender` cannot be the zero address.
+     */
+    function approve(address spender, uint256 value) public virtual returns (bool) {
+        address owner = _msgSender();
+        _approve(owner, spender, value);
+        return true;
+    }
+
+    /**
+     * @dev See {IERC20-transferFrom}.
+     *
+     * Skips emitting an {Approval} event indicating an allowance update. This is not
+     * required by the ERC. See {xref-ERC20-_approve-address-address-uint256-bool-}[_approve].
+     *
+     * NOTE: Does not update the allowance if the current allowance
+     * is the maximum `uint256`.
+     *
+     * Requirements:
+     *
+     * - `from` and `to` cannot be the zero address.
+     * - `from` must have a balance of at least `value`.
+     * - the caller must have allowance for ``from``'s tokens of at least
+     * `value`.
+     */
+    function transferFrom(address from, address to, uint256 value) public virtual returns (bool) {
+        address spender = _msgSender();
+        _spendAllowance(from, spender, value);
+        _transfer(from, to, value);
+        return true;
+    }
+}