[ios] Address Fabian's feedback

3 files changed, 8 insertions, 12 deletions

diff --git a/platform/darwin/src/MGLShapeSource.h b/platform/darwin/src/MGLShapeSource.h
index 8eb581dae1..967fb94544 100644
--- a/platform/darwin/src/MGLShapeSource.h
+++ b/platform/darwin/src/MGLShapeSource.h
@@ -42,12 +42,12 @@ FOUNDATION_EXTERN MGL_EXPORT const MGLShapeSourceOption MGLShapeSourceOptionClus
 FOUNDATION_EXTERN MGL_EXPORT const MGLShapeSourceOption MGLShapeSourceOptionClusterRadius;
 
 /**
- An `NSDictionary` object where the key is an `NSString`. The dictionary key will be the attribute feature attribute key. The resulting attribute value is aggregated from the clustered points.
+ An `NSDictionary` object where the key is an `NSString`. The dictionary key will be the attribute feature attribute key. The resulting attribute value is aggregated from the clustered points. The dictionary value is an `NSArray` consisting of a reduce operator and a map expression.
 
- The dictionary key is an `NSString` that will be an attribute key for the clusters. The dictionary value is an `NSArray` consisting of a reduce operator and a map expression.
+ The reduce operator is any `NSExpression` function that accepts at least two operands. You can use one of the following:
 
- The reduce operator is any `NSExpression` function that accepts at least two operands. It can be a string containing a single function, such as `sum:`, or a valid expression with two expression arguments: `featureAccumulated` and
- another valid expression.
+ * An `NSString` containing a single function, such as `sum` or `max`.
+ * An `NSExpression` that takes two expression arguments: `featureAccumulated` and another valid expression.
 
  The map expression is an `NSExpression` that produces the value of a single point within the cluster.
 
diff --git a/platform/darwin/src/MGLShapeSource.mm b/platform/darwin/src/MGLShapeSource.mm
index b806987267..00641c4a93 100644
--- a/platform/darwin/src/MGLShapeSource.mm
+++ b/platform/darwin/src/MGLShapeSource.mm
@@ -99,9 +99,9 @@ mbgl::style::GeoJSONOptions MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShap
             NSArray *expressionsArray = value[key];
             if (![expressionsArray isKindOfClass:[NSArray class]]) {
                 [NSException raise:NSInvalidArgumentException
-                            format:@"MGLShapeSourceOptionClusterProperties dictinary member value must be an array containing two objects."];
+                            format:@"MGLShapeSourceOptionClusterProperties dictionary member value must be an array containing two objects."];
             }
-            // check that array has only 2 values
+            // Check that the array has 2 values. One should be a the reduce expression and one should be the map expression.
             if ([expressionsArray count] != 2) {
                 [NSException raise:NSInvalidArgumentException
                             format:@"MGLShapeSourceOptionClusterProperties member value requires array of two objects."];
@@ -132,7 +132,7 @@ mbgl::style::GeoJSONOptions MGLGeoJSONOptionsFromDictionary(NSDictionary<MGLShap
             NSExpression *mapExpression = expressionsArray[1];
             if (![mapExpression isKindOfClass:[NSExpression class]]) {
                 [NSException raise:NSInvalidArgumentException
-                            format:@"MGLShapeSourceOptionClusterProperties member value shall contain a valid mapExpression.."];
+                            format:@"MGLShapeSourceOptionClusterProperties member value shall contain a valid mapExpression."];
             }
             auto map = MGLClusterPropertyFromNSExpression(mapExpression);
             if (!map) {
diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 93729f1bdf..9bbea4fa34 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -652,7 +652,6 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"let": @"MGL_LET",
         };
     });
-
     if (!object || object == [NSNull null]) {
         return [NSExpression expressionForConstantValue:nil];
     }
@@ -671,7 +670,6 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
         }];
         return [NSExpression expressionForConstantValue:dictionary];
     }
-    
     if ([object isKindOfClass:[NSArray class]]) {
         NSArray *array = (NSArray *)object;
         NSString *op = array.firstObject;
@@ -1056,9 +1054,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
         case NSFunctionExpressionType: {
             NSString *function = self.function;
 
-            BOOL hasCollectionProperty = !( ! [self.arguments.firstObject isKindOfClass: [NSExpression class]] || self.arguments.firstObject.expressionType == NSConstantValueExpressionType || self.arguments.firstObject.expressionType == NSKeyPathExpressionType
-            || self.arguments.firstObject.expressionType == NSVariableExpressionType
-                );
+            BOOL hasCollectionProperty = !( ! [self.arguments.firstObject isKindOfClass: [NSExpression class]] || self.arguments.firstObject.expressionType != NSAggregateExpressionType || self.arguments.firstObject.expressionType == NSSubqueryExpressionType);
             NSString *op = MGLExpressionOperatorsByFunctionNames[function];
             if (op) {
                 NSArray *arguments = self.arguments.mgl_jsonExpressionObject;