僅列出一些比較關(guān)鍵的點(diǎn)
可以看到里面定義的變量類型十分嚴(yán)謹(jǐn)，清楚地指定了類型的大小

AS_EXTERN int32_t const ASLayoutElementContextInvalidTransitionID;
AS_EXTERN int32_t const ASLayoutElementContextDefaultTransitionID;

在處理數(shù)組時(shí)，可以看到定義是很清晰的，通過定義靜態(tài)常量來定義數(shù)組的大小，更加直觀。

static const int kMaxLayoutElementBoolExtensions = 1;
static const int kMaxLayoutElementStateIntegerExtensions = 4;
static const int kMaxLayoutElementStateEdgeInsetExtensions = 1;

typedef struct ASLayoutElementStyleExtensions {
  // Values to store extensions
  BOOL boolExtensions[kMaxLayoutElementBoolExtensions];
  NSInteger integerExtensions[kMaxLayoutElementStateIntegerExtensions];
  UIEdgeInsets edgeInsetsExtensions[kMaxLayoutElementStateEdgeInsetExtensions];
} ASLayoutElementStyleExtensions;

通過宏定義了一些函數(shù)的默認(rèn)實(shí)現(xiàn)

#define ASLayoutElementLayoutCalculationDefaults \
- (ASLayout *)layoutThatFits:(ASSizeRange)constrainedSize\
{\
  return [self layoutThatFits:constrainedSize parentSize:constrainedSize.max];\
}\
\
- (ASLayout *)layoutThatFits:(ASSizeRange)constrainedSize parentSize:(CGSize)parentSize\
{\
  return [self calculateLayoutThatFits:constrainedSize restrictedToSize:self.style.size relativeToParentSize:parentSize];\
}\
\
- (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize\
                     restrictedToSize:(ASLayoutElementSize)size\
                 relativeToParentSize:(CGSize)parentSize\
{\
  const ASSizeRange resolvedRange = ASSizeRangeIntersect(constrainedSize, ASLayoutElementSizeResolve(self.style.size, parentSize));\
  return [self calculateLayoutThatFits:resolvedRange];\
}\

#define ASLayoutElementStyleExtensibilityForwarding \
- (void)setLayoutOptionExtensionBool:(BOOL)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionBool:value atIndex:idx];\
}\
\
- (BOOL)layoutOptionExtensionBoolAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionBoolAtIndex:idx];\
}\
\
- (void)setLayoutOptionExtensionInteger:(NSInteger)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionInteger:value atIndex:idx];\
}\
\
- (NSInteger)layoutOptionExtensionIntegerAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionIntegerAtIndex:idx];\
}\
\
- (void)setLayoutOptionExtensionEdgeInsets:(UIEdgeInsets)value atIndex:(int)idx\
{\
  [self.style setLayoutOptionExtensionEdgeInsets:value atIndex:idx];\
}\
\
- (UIEdgeInsets)layoutOptionExtensionEdgeInsetsAtIndex:(int)idx\
{\
  return [self.style layoutOptionExtensionEdgeInsetsAtIndex:idx];\
}\