intitial ERC4626 implementation

contracts/token/ERC20/extensions/draft-ERC4646.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../ERC20.sol";
+import "../utils/SafeERC20.sol";
+import "../../../interfaces/draft-IERC4626.sol";
+
+abstract contract ERC4262 is ERC20, IERC4626 {
+    IERC20 private immutable _asset;
+
+    constructor (IERC20 __asset) {
+        _asset = __asset;
+    }
+
+    function asset() public view virtual override returns (address) {
+        return address(_asset);
+    }
+
+    function totalAssets() public view virtual override returns (uint256) {
+        return _asset.balanceOf(address(this));
+    }
+
+    function assetsPerShare() public view virtual override returns (uint256) {
+        return _sharesToAssets(10 ** decimals());
+    }
+
+    function assetsOf(address depositor) public view virtual override returns (uint256) {
+        return totalAssets() * balanceOf(depositor) / totalSupply();
+    }
+
+    function maxDeposit(address /*caller*/) public view virtual override returns (uint256) {
+        return type(uint256).max;
+    }
+
+    function previewDeposit(uint256 assets) public view virtual override returns (uint256) {
+        return _assetsToShares(assets);
+    }
+
+    function deposit(uint256 assets, address receiver) public virtual override returns (uint256) {
+        uint256 shares = previewDeposit(assets);
+        SafeERC20.safeTransferFrom(_asset, _msgSender(), address(this), assets);
+        _mint(receiver, shares);
+        return shares;
+    }
+
+    function maxMint(address /*caller*/) public view virtual override returns (uint256) {
+        return type(uint256).max;
+    }
+
+    function previewMint(uint256 shares) public view virtual override returns (uint256) {
+        return _sharesToAssets(shares);
+    }
+
+    function mint(uint256 shares, address receiver) public virtual override returns (uint256) {
+        uint256 assets = _sharesToAssets(shares);
+        SafeERC20.safeTransferFrom(_asset, _msgSender(), address(this), assets);
+        _mint(receiver, shares);
+        return assets;
+    }
+
+    function maxWithdraw(address caller) public view virtual override returns (uint256) {
+        return assetsOf(caller);
+    }
+
+    function previewWithdraw(uint256 assets) public view virtual override returns (uint256) {
+        return _assetsToShares(assets);
+    }
+
+    function withdraw(uint256 assets, address receiver, address owner) public virtual override returns (uint256) {
+        address sender = _msgSender();
+        uint256 shares = previewWithdraw(assets);
+
+        if (sender != owner) {
+            uint256 currentAllowance = allowance(owner, sender);
+            if (currentAllowance != type(uint256).max) {
+                require(currentAllowance >= shares, "ERC20: transfer amount exceeds allowance");
+                unchecked {
+                    _approve(owner, sender, currentAllowance - shares);
+                }
+            }
+        }
+
+        _burn(owner, shares);
+        SafeERC20.safeTransfer(_asset, receiver, assets);
+        return shares;
+    }
+
+    function maxRedeem(address caller) public view virtual override returns (uint256) {
+        return balanceOf(caller);
+    }
+
+    function previewRedeem(uint256 shares) public view virtual override returns (uint256) {
+        return _sharesToAssets(shares);
+    }
+
+    function redeem(uint256 shares, address receiver, address owner) public virtual override returns (uint256) {
+        address sender = _msgSender();
+        uint256 assets = previewRedeem(shares);
+
+        if (sender != owner) {
+            uint256 currentAllowance = allowance(owner, sender);
+            if (currentAllowance != type(uint256).max) {
+                require(currentAllowance >= shares, "ERC20: transfer amount exceeds allowance");
+                unchecked {
+                    _approve(owner, sender, currentAllowance - shares);
+                }
+            }
+        }
+
+        _burn(owner, shares);
+        SafeERC20.safeTransfer(_asset, receiver, assets);
+        return assets;
+    }
+
+    function _sharesToAssets(uint256 shares) internal view virtual returns (uint256) {
+        return totalSupply() == 0 ? shares : shares * totalAssets() / totalSupply();
+    }
+
+    function _assetsToShares(uint256 assets) internal view virtual returns (uint256) {
+        return totalAssets() == 0 ? assets : assets * totalSupply() / totalAssets();
+    }
+}