adjust sample implementation to match interface

EIPS/eip-7246.md

@@ -84,14 +84,14 @@ interface IERC7246{
      *
      * Emits a {Release} event.
      */
-    function release(address owner, uint amount);
+    function release(address owner, uint amount) external;
 
 
     /**
      * @dev Convenience function for reading the unencumbered balance of an address.
      * Trivially implemented as `balanceOf(owner) - encumberedBalanceOf(owner)`
      */
-    function availableBalanceOf(address owner) external returns (uint);
+    function availableBalanceOf(address owner) public view returns (uint);
 }
 ```
 
@@ -111,60 +111,53 @@ This can be implemented as an extension of any base [ERC-20](./eip-20.md) contra
 
 
 ``` solidity
-
 // An erc-20 token that implements the encumber interface by blocking transfers.
 
 pragma solidity ^0.8.0;
 import {ERC20} from "../lib/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
+import { IERC7246 } from "./IERC7246.sol";
 
-contract EncumberableERC20 is ERC20 {
+contract EncumberableERC20 is ERC20, IERC7246 {
     // Owner -> Taker -> Amount that can be taken
     mapping (address => mapping (address => uint)) public encumbrances;
 
     // The encumbered balance of the token owner. encumberedBalance must not exceed balanceOf for a user
     // Note this means rebasing tokens pose a risk of diminishing and violating this prototocol
-    mapping (address => uint) public encumberedBalance;
+    mapping (address => uint) public encumberedBalanceOf;
     
     address public minter;
 
-    event Encumber(address indexed owner, address indexed taker, uint encumberedAmount);
-    event Release(address indexed owner, address indexed taker, uint releasedAmount);
-
     constructor(string memory name, string memory symbol) ERC20(name, symbol) {
         minter = msg.sender;
     }
 
-    function mint(address recipient, uint amount) public virtual returns (bool) {
+    function mint(address recipient, uint amount) public {
         require(msg.sender == minter, "only minter");
         _mint(recipient, amount);
-        return true;
     }
 
-    function encumber(address taker, uint amount) public virtual returns (bool) {
+    function encumber(address taker, uint amount) external {
         _encumber(msg.sender, taker, amount);
-        return true;
     }
 
-    function encumberFrom(address owner, address taker, uint amount) public virtual returns (bool) {
+    function encumberFrom(address owner, address taker, uint amount) external {
         require(allowance(owner, msg.sender) >= amount);
        _encumber(owner, taker, amount);
-       return true;
     }
 
-    function release(address owner, uint amount) public virtual returns (bool) {
+    function release(address owner, uint amount) external {
         _release(owner, msg.sender, amount);
-        return true;
     }
 
     // If bringing balance and encumbrances closer to equal, must check
     function availableBalanceOf(address a) public view returns (uint) {
-        return (balanceOf(a) - encumberedBalance[a]);
+        return (balanceOf(a) - encumberedBalanceOf[a]);
     }
 
     function _encumber(address owner, address taker, uint amount) private {
         require(availableBalanceOf(owner) >= amount, "insufficient balance");
         encumbrances[owner][taker] += amount;
-        encumberedBalance[owner] += amount;
+        encumberedBalanceOf[owner] += amount;
         emit Encumber(owner, taker, amount);
     }
 
@@ -173,7 +166,7 @@ contract EncumberableERC20 is ERC20 {
           amount = encumbrances[owner][taker];
         }
         encumbrances[owner][taker] -= amount;
-        encumberedBalance[owner] -= amount;
+        encumberedBalanceOf[owner] -= amount;
         emit Release(owner, taker, amount);
     }
 
@@ -212,7 +205,7 @@ contract EncumberableERC20 is ERC20 {
         require(currentEncumbrance >= amount, "insufficient encumbrance");
         uint newEncumbrance = currentEncumbrance - amount;
         encumbrances[owner][taker] = newEncumbrance;
-        encumberedBalance[owner] -= amount;
+        encumberedBalanceOf[owner] -= amount;
     }
 }
 ```