Make _asset overrideable in ERC4626

Author: ernestognw

contracts/token/ERC20/extensions/ERC4626.sol

@@ -114,7 +114,7 @@ abstract contract ERC4626 is ERC20, IERC4626 {
 
     /** @dev See {IERC4626-totalAssets}. */
     function totalAssets() public view virtual returns (uint256) {
-        return _asset.balanceOf(address(this));
+        return IERC20(asset()).balanceOf(address(this));
     }
 
     /** @dev See {IERC4626-convertToShares}. */
@@ -237,14 +237,14 @@ abstract contract ERC4626 is ERC20, IERC4626 {
      * @dev Deposit/mint common workflow.
      */
     function _deposit(address caller, address receiver, uint256 assets, uint256 shares) internal virtual {
-        // If _asset is ERC-777, `transferFrom` can trigger a reentrancy BEFORE the transfer happens through the
+        // If asset() is ERC-777, `transferFrom` can trigger a reentrancy BEFORE the transfer happens through the
         // `tokensToSend` hook. On the other hand, the `tokenReceived` hook, that is triggered after the transfer,
         // calls the vault, which is assumed not malicious.
         //
         // Conclusion: we need to do the transfer before we mint so that any reentrancy would happen before the
         // assets are transferred and before the shares are minted, which is a valid state.
         // slither-disable-next-line reentrancy-no-eth
-        SafeERC20.safeTransferFrom(_asset, caller, address(this), assets);
+        SafeERC20.safeTransferFrom(IERC20(asset()), caller, address(this), assets);
         _mint(receiver, shares);
 
         emit Deposit(caller, receiver, assets, shares);
@@ -264,14 +264,14 @@ abstract contract ERC4626 is ERC20, IERC4626 {
             _spendAllowance(owner, caller, shares);
         }
 
-        // If _asset is ERC-777, `transfer` can trigger a reentrancy AFTER the transfer happens through the
+        // If asset() is ERC-777, `transfer` can trigger a reentrancy AFTER the transfer happens through the
         // `tokensReceived` hook. On the other hand, the `tokensToSend` hook, that is triggered before the transfer,
         // calls the vault, which is assumed not malicious.
         //
         // Conclusion: we need to do the transfer after the burn so that any reentrancy would happen after the
         // shares are burned and after the assets are transferred, which is a valid state.
         _burn(owner, shares);
-        SafeERC20.safeTransfer(_asset, receiver, assets);
+        SafeERC20.safeTransfer(IERC20(asset()), receiver, assets);
 
         emit Withdraw(caller, receiver, owner, assets, shares);
     }