[ios, macos] Implemented type conversion using CAST()

3 files changed, 28 insertions, 2 deletions

diff --git a/platform/darwin/docs/guides/Predicates and Expressions.md b/platform/darwin/docs/guides/Predicates and Expressions.md
index 06eaabbdbe..97834b4f71 100644
--- a/platform/darwin/docs/guides/Predicates and Expressions.md
+++ b/platform/darwin/docs/guides/Predicates and Expressions.md
@@ -162,6 +162,7 @@ Initializer parameter | Format string syntax
 `lowercase:`          | `lowercase('DOWNTOWN')`
 `noindex:`            | `noindex(0 + 2 + c)`
 `length:`             | `length('Wapakoneta')`
+`castObject:toType:`  | `CAST(ele, 'NSString')`<br>`CAST(ele, 'NSNumber')`
 
 The following predefined functions are not supported:
 
diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 3c159430af..43661a5502 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -421,12 +421,15 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             return [NSExpression expressionForFunction:operand selectorName:@"boolValue" arguments:@[]];
         } else if ([op isEqualToString:@"to-number"]) {
             NSExpression *operand = [NSExpression mgl_expressionWithJSONObject:argumentObjects.firstObject];
+            if (argumentObjects.count == 1) {
+                return [NSExpression expressionWithFormat:@"CAST(%@, 'NSNumber')", operand];
+            }
             argumentObjects = [argumentObjects subarrayWithRange:NSMakeRange(1, argumentObjects.count - 1)];
             NSArray *subexpressions = MGLSubexpressionsWithJSONObjects(argumentObjects);
             return [NSExpression expressionForFunction:operand selectorName:@"mgl_numberWithFallbackValues:" arguments:subexpressions];
         } else if ([op isEqualToString:@"to-string"]) {
             NSExpression *operand = [NSExpression mgl_expressionWithJSONObject:argumentObjects.firstObject];
-            return [NSExpression expressionForFunction:operand selectorName:@"stringValue" arguments:@[]];
+            return [NSExpression expressionWithFormat:@"CAST(%@, 'NSString')", operand];
         } else if ([op isEqualToString:@"get"]) {
             if (argumentObjects.count == 2) {
                 NSExpression *operand = [NSExpression mgl_expressionWithJSONObject:argumentObjects.lastObject];
@@ -820,6 +823,16 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
                 }
                 
                 return expressionObject;
+            } else if ([function isEqualToString:@"castObject:toType:"]) {
+                id object = self.arguments.firstObject.mgl_jsonExpressionObject;
+                NSString *type = self.arguments[1].mgl_jsonExpressionObject;
+                if ([type isEqualToString:@"NSString"]) {
+                    return @[@"to-string", object];
+                } else if ([type isEqualToString:@"NSNumber"]) {
+                    return @[@"to-number", object];
+                }
+                [NSException raise:NSInvalidArgumentException
+                            format:@"Casting expression to %@ not yet implemented.", type];
             } else if ([function isEqualToString:@"median:"] ||
                        [function isEqualToString:@"mode:"] ||
                        [function isEqualToString:@"stddev:"] ||
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 807e7ffa00..5451174e24 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -560,10 +560,22 @@ using namespace std::string_literals;
         XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
     }
     {
-        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(number, 'stringValue')"];
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(postalCode, 'NSNumber')"];
+        NSExpression *compatibilityExpression = [NSExpression expressionWithFormat:@"FUNCTION(postalCode, 'mgl_numberWithFallbackValues:')"];
+        NSArray *jsonExpression = @[@"to-number", @[@"get", @"postalCode"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects(compatibilityExpression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:@{@"postalCode": @"02134"} context:nil], @02134);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"CAST(number, 'NSString')"];
+        NSExpression *compatibilityExpression = [NSExpression expressionWithFormat:@"FUNCTION(number, 'stringValue')"];
         NSArray *jsonExpression = @[@"to-string", @[@"get", @"number"]];
         XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects(compatibilityExpression.mgl_jsonExpressionObject, jsonExpression);
         XCTAssertEqualObjects([expression expressionValueWithObject:@{@"number": @1.5} context:nil], @"1.5");
+        XCTAssertEqualObjects([compatibilityExpression expressionValueWithObject:@{@"number": @1.5} context:nil], @"1.5");
         XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
     }
 }