Nonfungible ERC1155 implementation

contracts/token/ERC1155/extensions/ERC1155Nonfungible.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {ERC1155} from "../ERC1155.sol";
+import {Arrays} from "../../../utils/Arrays.sol";
+
+/**
+ * @dev Indicates that the operator is trying to mint a token that already exists.
+ * @param id Identifier of token being minted
+ * @param owner Current token owner
+ */
+error ERC1155NonfungibleDuplicate(uint256 id, address owner);
+
+/**
+ * @dev Indicates that the operator is trying mint/transfer/burn an amount > 1 of a token
+ */
+error ERC1155NonfungibleInvalidAmount(uint256 id, uint256 amount);
+
+/**
+ * @dev For tokens that are nonfungible but prefer to use {ERC1155} rather than {ERC721}.
+ *
+ * {ERC1155Nonfungible} takes advantage of nonfungibility constraint to replace data model
+ * tracking multiple account balances per token with with a more gas-efficient data model
+ * tracking unique ownership per token.
+ * 
+ * Moreover {ERC1155Nonfungible} makes it possible to query the owner of a specific token via {ERC1155Nonfungible-ownerOf},
+ * similar to {ERC721-ownerOf}, but differs from {ERC721-ownerOf} in that querying the owner of an inexistent token
+ * will not revert but will return `address(0)`.
+ */
+abstract contract ERC1155Nonfungible is ERC1155 {
+    using Arrays for uint256[];
+    using Arrays for address[];
+
+    mapping(uint256 id => address) private _owners;
+
+    /**
+     * @dev Returns the owner of the token `id`. Does NOT revert if token doesn't exist.
+     * 
+     * {ERC1155Nonfungible-ownerOf} and {ERC1155Nonfungible-_setOwnerOf} may be overridden in tandem,
+     * e.g. to store more token information along with the owner
+     */
+    function ownerOf(uint256 id) public view virtual returns (address) {
+        return _owners[id];
+    }
+
+    /**
+     * @dev {ERC1155Nonfungible-ownerOf} and {ERC1155Nonfungible-_setOwnerOf} may be overridden in tandem,
+     * e.g. to store more token information along with the owner
+     */
+    function _setOwnerOf(uint256 id, address owner) internal virtual {
+        _owners[id] = owner;
+    }
+
+    /**
+     * @dev Replaces {ERC1155-balanceOf} implementation entirely.
+     */
+    function balanceOf(address account, uint256 id) public view virtual override returns (uint256) {
+        return account != address(0) && ownerOf(id) == account ? 1 : 0;
+    }
+
+    /**
+     * @dev Replaces {ERC1155-_update} implementation entirely.
+     */
+    function _update(address from, address to, uint256[] memory ids, uint256[] memory values) internal virtual override {
+        if (ids.length != values.length) {
+            revert ERC1155InvalidArrayLength(ids.length, values.length);
+        }
+
+        address operator = _msgSender();
+
+        for (uint256 i = 0; i < ids.length; ++i) {
+            uint256 id = ids.unsafeMemoryAccess(i);
+            uint256 value = values.unsafeMemoryAccess(i);
+
+            if (value == 1) {
+                address currOwner = ownerOf(id);
+                // Could be written more compactly, but clearer if mint tackled separately from transfer/burn
+                if (from == address(0)) {
+                    if (currOwner == address(0)) {
+                        _setOwnerOf(id, to);
+                    } else {
+                        revert ERC1155NonfungibleDuplicate(id, currOwner);
+                    }
+                } else {
+                    if (from == currOwner) {
+                        _setOwnerOf(id, to);
+                    } else {
+                        revert ERC1155InsufficientBalance({ sender: from, balance: 0, needed: 1, tokenId: id });
+                    }
+                }
+            } else if (value == 0) {
+                // ERC-1155 allows zero-value transfers
+            } else {
+                revert ERC1155NonfungibleInvalidAmount(id, value);
+            }
+        }
+
+        if (ids.length == 1) {
+            uint256 id = ids.unsafeMemoryAccess(0);
+            uint256 value = values.unsafeMemoryAccess(0);
+            emit TransferSingle(operator, from, to, id, value);
+        } else {
+            emit TransferBatch(operator, from, to, ids, values);
+        }
+    }
+}