Implement NSArray mappers

Riot/Categories/NSArray+Element.m

@@ -0,0 +1,55 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#import "NSArray+Element.h"
+
+@implementation NSArray (Element)
+
+- (NSArray *)vc_map:(id (^)(id obj))block
+{
+    NSMutableArray *result = [NSMutableArray arrayWithCapacity:self.count];
+    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
+    {
+        [result addObject:block(obj)];
+    }];
+    return result;
+}
+
+- (NSArray *)vc_compactMap:(id _Nullable (^)(id obj))block
+{
+    NSMutableArray *result = [NSMutableArray arrayWithCapacity:self.count];
+    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
+    {
+        id mappedObject = block(obj);
+        if (mappedObject)
+        {
+            [result addObject:mappedObject];
+        }
+    }];
+    return result;
+}
+
+- (NSArray *)vc_flatMap:(NSArray* (^)(id obj))block
+{
+    NSMutableArray *result = [NSMutableArray arrayWithCapacity:self.count];
+    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
+    {
+        [result addObjectsFromArray:block(obj)];
+    }];
+    return result;
+}
+
+@end