Support custom map types in resolvers (e.g.

`type Thing map[string]interface{}`) by falling back to reflection.
Fixes #439.

Author: atombender

executor.go

@@ -964,6 +964,22 @@ func DefaultResolveFn(p ResolveParams) (interface{}, error) {
 		return property, nil
 	}
 
+	// Try accessing as map via reflection
+	if r := reflect.ValueOf(p.Source); r.Kind() == reflect.Map && r.Type().Key().Kind() == reflect.String {
+		val := r.MapIndex(reflect.ValueOf(p.Info.FieldName))
+		if val.IsValid() {
+			property := val.Interface()
+			if val.Type().Kind() == reflect.Func {
+				// try type casting the func to the most basic func signature
+				// for more complex signatures, user have to define ResolveFn
+				if propertyFn, ok := property.(func() interface{}); ok {
+					return propertyFn(), nil
+				}
+			}
+			return property, nil
+		}
+	}
+
 	// last resort, return nil
 	return nil, nil
 }