ERC721 extension for efficient batch minting (#3311)

Co-authored-by: Francisco <frangio.1@gmail.com>

scripts/generate/templates/Checkpoints.js

@@ -32,14 +32,6 @@ struct ${opts.checkpointTypeName} {
 
 /* eslint-disable max-len */
 const operations = opts => `\
-/**
- * @dev Returns the value in the most recent checkpoint, or zero if there are no checkpoints.
- */
-function latest(${opts.historyTypeName} storage self) internal view returns (${opts.valueTypeName}) {
-    uint256 pos = self.${opts.checkpointFieldName}.length;
-    return pos == 0 ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1).${opts.valueFieldName};
-}
-
 /**
  * @dev Pushes a (\`key\`, \`value\`) pair into a ${opts.historyTypeName} so that it is stored as the checkpoint.
  *
@@ -73,14 +65,6 @@ function upperLookup(${opts.historyTypeName} storage self, ${opts.keyTypeName} k
 `;
 
 const legacyOperations = opts => `\
-/**
- * @dev Returns the value in the latest checkpoint, or zero if there are no checkpoints.
- */
-function latest(${opts.historyTypeName} storage self) internal view returns (uint256) {
-    uint256 pos = self.${opts.checkpointFieldName}.length;
-    return pos == 0 ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1).${opts.valueFieldName};
-}
-
 /**
  * @dev Returns the value at a given block number. If a checkpoint is not available at that block, the closest one
  * before it is returned, or zero otherwise.
@@ -147,7 +131,44 @@ function push(
 }
 `;
 
-const helpers = opts => `\
+const common = opts => `\
+/**
+ * @dev Returns the value in the most recent checkpoint, or zero if there are no checkpoints.
+ */
+function latest(${opts.historyTypeName} storage self) internal view returns (${opts.valueTypeName}) {
+    uint256 pos = self.${opts.checkpointFieldName}.length;
+    return pos == 0 ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1).${opts.valueFieldName};
+}
+
+/**
+ * @dev Returns whether there is a checkpoint in the structure (i.e. it is not empty), and if so the key and value
+ * in the most recent checkpoint.
+ */
+function latestCheckpoint(${opts.historyTypeName} storage self)
+    internal
+    view
+    returns (
+        bool exists,
+        ${opts.keyTypeName} ${opts.keyFieldName},
+        ${opts.valueTypeName} ${opts.valueFieldName}
+    )
+{
+    uint256 pos = self.${opts.checkpointFieldName}.length;
+    if (pos == 0) {
+        return (false, 0, 0);
+    } else {
+        ${opts.checkpointTypeName} memory ckpt = _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1);
+        return (true, ckpt.${opts.keyFieldName}, ckpt.${opts.valueFieldName});
+    }
+}
+
+/**
+ * @dev Returns the number of checkpoint.
+ */
+function length(${opts.historyTypeName} storage self) internal view returns (uint256) {
+    return self.${opts.checkpointFieldName}.length;
+}
+
 /**
  * @dev Pushes a (\`key\`, \`value\`) pair into an ordered list of checkpoints, either by inserting a new checkpoint,
  * or by updating the last one.
@@ -266,12 +287,12 @@ module.exports = format(
     // Legacy types & functions
     types(LEGACY_OPTS),
     legacyOperations(LEGACY_OPTS),
-    helpers(LEGACY_OPTS),
+    common(LEGACY_OPTS),
     // New flavors
     ...OPTS.flatMap(opts => [
       types(opts),
       operations(opts),
-      helpers(opts),
+      common(opts),
     ]),
   ],
   '}',

scripts/generate/templates/CheckpointsMock.js

@@ -18,6 +18,14 @@ contract CheckpointsMock {
         return _totalCheckpoints.latest();
     }
 
+    function latestCheckpoint() public view returns (bool, uint256, uint256) {
+        return _totalCheckpoints.latestCheckpoint();
+    }
+
+    function length() public view returns (uint256) {
+        return _totalCheckpoints.length();
+    }
+
     function push(uint256 value) public returns (uint256, uint256) {
         return _totalCheckpoints.push(value);
     }
@@ -29,10 +37,6 @@ contract CheckpointsMock {
     function getAtProbablyRecentBlock(uint256 blockNumber) public view returns (uint256) {
         return _totalCheckpoints.getAtProbablyRecentBlock(blockNumber);
     }
-
-    function length() public view returns (uint256) {
-        return _totalCheckpoints._checkpoints.length;
-    }
 }
 `;
 
@@ -46,6 +50,14 @@ contract Checkpoints${length}Mock {
         return _totalCheckpoints.latest();
     }
 
+    function latestCheckpoint() public view returns (bool, uint${256 - length}, uint${length}) {
+        return _totalCheckpoints.latestCheckpoint();
+    }
+
+    function length() public view returns (uint256) {
+        return _totalCheckpoints.length();
+    }
+
     function push(uint${256 - length} key, uint${length} value) public returns (uint${length}, uint${length}) {
         return _totalCheckpoints.push(key, value);
     }
@@ -57,10 +69,6 @@ contract Checkpoints${length}Mock {
     function upperLookup(uint${256 - length} key) public view returns (uint${length}) {
         return _totalCheckpoints.upperLookup(key);
     }
-
-    function length() public view returns (uint256) {
-        return _totalCheckpoints._checkpoints.length;
-    }
 }
 `;