3 files changed, 33 insertions, 7 deletions
diff --git a/platform/darwin/src/MGLStyleValue.h b/platform/darwin/src/MGLStyleValue.h
index 1f19a5e028..010a0d68cb 100644
--- a/platform/darwin/src/MGLStyleValue.h
+++ b/platform/darwin/src/MGLStyleValue.h
@@ -13,7 +13,9 @@
 
 + (instancetype)valueWithRawValue:(T)rawValue;
 
-- (instancetype)initWithRawValue:(T)rawValue;
+- (instancetype)init NS_UNAVAILABLE;
+
+- (instancetype)initWithRawValue:(T)rawValue NS_DESIGNATED_INITIALIZER;
 
 @property (nonatomic) T rawValue;
 
@@ -22,9 +24,10 @@
 @interface MGLStyleFunction<T> : MGLStyleValue
 
 + (instancetype)functionWithBase:(CGFloat)base stops:(NSDictionary<NSNumber *, MGLStyleValue<T> *> *)stops;
+
 + (instancetype)functionWithStops:(NSDictionary<NSNumber *, MGLStyleValue<T> *> *)stops;
 
-- (instancetype)initWithBase:(CGFloat)base stops:(NSDictionary<NSNumber *, MGLStyleValue<T> *> *)stops;
+- (instancetype)initWithBase:(CGFloat)base stops:(NSDictionary<NSNumber *, MGLStyleValue<T> *> *)stops NS_DESIGNATED_INITIALIZER;
 
 @property (nonatomic) CGFloat base;
 @property (nonatomic, copy) NSDictionary<NSNumber *, MGLStyleValue<T> *> *stops;
diff --git a/platform/darwin/src/MGLStyleValue.mm b/platform/darwin/src/MGLStyleValue.mm
index f8d5fd3a5d..43b51d6788 100644
--- a/platform/darwin/src/MGLStyleValue.mm
+++ b/platform/darwin/src/MGLStyleValue.mm
@@ -33,6 +33,10 @@
     return [self.rawValue description];
 }
 
+- (NSString *)debugDescription {
+    return [self.rawValue debugDescription];
+}
+
 - (BOOL)isEqual:(MGLStyleConstantValue *)other {
     return [other isKindOfClass:[self class]] && [other.rawValue isEqual:self.rawValue];
 }
@@ -54,18 +58,31 @@
 }
 
 - (instancetype)init {
-    if (self = [super init]) {
-        _base = 1;
-    }
-    return self;
+    return [self initWithBase:1 stops:@{}];
 }
 
 - (instancetype)initWithBase:(CGFloat)base stops:(NSDictionary *)stops {
-    if (self = [self init]) {
+    if (self = [super init]) {
         _base = base;
         _stops = stops;
     }
     return self;
 }
 
+- (NSString *)description {
+    return [NSString stringWithFormat:@"<%@: %p, base = %f; stops = %@>",
+            NSStringFromClass([self class]), (void *)self,
+            self.base,
+            self.stops];
+}
+
+- (BOOL)isEqual:(MGLStyleFunction *)other {
+    return ([other isKindOfClass:[self class]] && other.base == self.base
+            && [other.stops isEqualToDictionary:self.stops]);
+}
+
+- (NSUInteger)hash {
+    return self.base + self.stops.hash;
+}
+
 @end
diff --git a/platform/darwin/src/MGLStyleValue_Private.h b/platform/darwin/src/MGLStyleValue_Private.h
index e48db02bf1..cc3fecec7e 100644
--- a/platform/darwin/src/MGLStyleValue_Private.h
+++ b/platform/darwin/src/MGLStyleValue_Private.h
@@ -42,6 +42,12 @@ public:
                 mbglStops.emplace_back(zoomKey.floatValue, mbglStopValue.asConstant());
             }];
             return mbgl::style::Function<MBGLType>({{mbglStops}}, function.base);
+        } else if (value) {
+            [NSException raise:@"MGLAbstractClassException" format:
+             @"The style value %@ cannot be applied to the style. "
+             @"Make sure the style value was created as a member of a concrete subclass of MGLStyleValue.",
+             NSStringFromClass([value class])];
+            return {};
         } else {
             return {};
         }