Introduce type property to replace layout id check

AsyncDisplayKit/ASDisplayNode.mm

@@ -62,7 +62,9 @@ NSString * const ASRenderingEngineDidDisplayNodesScheduledBeforeTimestamp = @"AS
 @implementation ASDisplayNode
 
 // these dynamic properties all defined in ASLayoutOptionsPrivate.m
-@dynamic spacingAfter, spacingBefore, flexGrow, flexShrink, flexBasis, alignSelf, ascender, descender, sizeRange, layoutPosition;
+@dynamic spacingAfter, spacingBefore, flexGrow, flexShrink, flexBasis,
+         alignSelf, ascender, descender, sizeRange, layoutPosition, layoutableType;
+
 @synthesize name = _name;
 @synthesize preferredFrameSize = _preferredFrameSize;
 @synthesize isFinalLayoutable = _isFinalLayoutable;
@@ -659,6 +661,11 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   return _layout == nil || _layout.isDirty;
 }
 
+- (ASLayoutableType)layoutableType
+{
+  return ASLayoutableTypeDisplayNode;
+}
+
 #pragma mark - Layout Transition
 
 - (void)transitionLayoutWithAnimation:(BOOL)animated

AsyncDisplayKit/Layout/ASLayout.h

@@ -31,6 +31,11 @@ extern BOOL CGPointIsNull(CGPoint point);
  */
 @property (nonatomic, weak, readonly) id<ASLayoutable> layoutableObject;
 
+/**
+ * The type of ASLayoutable that created this layout
+ */
+@property (nonatomic, readonly) ASLayoutableType type;
+
 /**
  * Size of the current layout
  */

AsyncDisplayKit/Layout/ASLayout.mm

@@ -12,7 +12,6 @@
 
 #import "ASAssert.h"
 #import "ASDimension.h"
-#import "ASDisplayNode.h"
 #import "ASInternalHelpers.h"
 #import "ASLayoutSpecUtilities.h"
 
@@ -36,7 +35,7 @@ extern BOOL CGPointIsNull(CGPoint point)
 
 @implementation ASLayout
 
-@dynamic frame;
+@dynamic frame, type;
 
 - (instancetype)initWithLayoutableObject:(id<ASLayoutable>)layoutableObject
                     constrainedSizeRange:(ASSizeRange)sizeRange
@@ -159,7 +158,7 @@ extern BOOL CGPointIsNull(CGPoint point)
     Context context = queue.front();
     queue.pop();
 
-    if (self != context.layout && [context.layout.layoutableObject isKindOfClass:[ASDisplayNode class]]) {
+    if (self != context.layout && context.layout.type == ASLayoutableTypeDisplayNode) {
       ASLayout *layout = [ASLayout layoutWithLayout:context.layout position:context.absolutePosition];
       layout.flattened = YES;
       [flattenedSublayouts addObject:layout];
@@ -178,6 +177,13 @@ extern BOOL CGPointIsNull(CGPoint point)
                                    sublayouts:flattenedSublayouts];
 }
 
+#pragma mark - Accessors
+
+- (ASLayoutableType)type
+{
+  return _layoutableObject.layoutableType;
+}
+
 - (CGRect)frame
 {
   CGRect subnodeFrame = CGRectZero;

AsyncDisplayKit/Layout/ASLayoutSpec.mm

@@ -34,7 +34,8 @@
 @implementation ASLayoutSpec
 
 // these dynamic properties all defined in ASLayoutOptionsPrivate.m
-@dynamic spacingAfter, spacingBefore, flexGrow, flexShrink, flexBasis, alignSelf, ascender, descender, sizeRange, layoutPosition;
+@dynamic spacingAfter, spacingBefore, flexGrow, flexShrink, flexBasis,
+         alignSelf, ascender, descender, sizeRange, layoutPosition, layoutableType;
 @synthesize isFinalLayoutable = _isFinalLayoutable;
 
 - (instancetype)init
@@ -48,6 +49,11 @@
   return self;
 }
 
+- (ASLayoutableType)layoutableType
+{
+  return ASLayoutableTypeLayoutSpec;
+}
+
 #pragma mark - Layout
 
 - (ASLayout *)measureWithSizeRange:(ASSizeRange)constrainedSize

AsyncDisplayKit/Layout/ASLayoutable.h

@@ -21,6 +21,11 @@
 @class ASLayout;
 @class ASLayoutSpec;
 
+typedef NS_ENUM(NSUInteger, ASLayoutableType) {
+  ASLayoutableTypeLayoutSpec,
+  ASLayoutableTypeDisplayNode
+};
+
 NS_ASSUME_NONNULL_BEGIN
 
 /** 
@@ -41,6 +46,8 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @protocol ASLayoutable <ASEnvironment, ASStackLayoutable, ASStaticLayoutable, ASLayoutablePrivate, ASLayoutableExtensibility>
 
+@property (nonatomic, readonly) ASLayoutableType layoutableType;
+
 /**
  * @abstract Calculate a layout based on given size range.
  *
@@ -50,7 +57,6 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (ASLayout *)measureWithSizeRange:(ASSizeRange)constrainedSize;
 
-
 #pragma mark - Layout options from the Layoutable Protocols
 
 #pragma mark - ASStackLayoutable