如何在Flex中使用位图图像创建反射效果？(How can I create a reflection effect with bitmap images in Flex?)

 C ++ 03中有许多部分不允许嵌套类的前向声明。 特别是§7.1.5.3详细的类型说明符： 
 
 
 
 
  
 如果一个详细类型说明符是一个声明的唯一组成部分，那么该声明是不健全的，除非它是一个明确的专门化（14.7.3），一个明确的实例化（14.7.2）或者它具有以下形式之一： 
class-key identifier ; 
friend class-key ::opt identifier ; 
friend class-key ::opt template-id ; 
friend class-key ::opt nested-name-specifier identifier ; 
friend class-key ::opt nested-name-specifier templateopt
template-id ;
 
  
 3.4.4描述了名称查找在标注类型说明 符中如何继续标识符 。 如果标识符解析为类名或枚举名 ，则详细类型说明符将其引入到声明中，这与简单类型说明符介绍其类型名称的方式相同 。 [...]如果名称查找没有找到该名称的声明，则详细说明类型说明符是格式错误的，除非它是简单形式的类关键 标识符，在这种情况下， 标识符是按3.3中所述进行声明的。 1。 
 
 
 
 
 简而言之，当一个标识符被作用域时，编译器必须尝试解析该标识符。 当范围是一个类时，编译器必须在外部类中查找该标识符的声明。 当外部类还没有被定义时，这是不能完成的，结果是一个不合格的程序。 

There are a number of parts of C++03 that disallow forward declarations of nested classes. In particular, § 7.1.5.3 Elaborated type specifiers:
 
 
 
 
  
If an elaborated-type-specifier is the sole constituent of a declaration, the declaration is ill-formed unless it is an explicit specialization (14.7.3), an explicit instantiation (14.7.2) or it has one of the following forms:
 
class-key identifier ; 
friend class-key ::opt identifier ; 
friend class-key ::opt template-id ; 
friend class-key ::opt nested-name-specifier identifier ; 
friend class-key ::opt nested-name-specifier templateopt
template-id ;
 
 
  
3.4.4 describes how name lookup proceeds for the identifier in an elaborated-type-specifier. If the identifier resolves to a class-name or enum-name, the elaborated-type-specifier introduces it into the declaration the same way a simple-type-specifier introduces its type-name. [...] If name lookup does not find a declaration for the name, the elaborated-type-specifier is ill-formed unless it is of the simple form class-key identifier in which case the identifier is declared as described in 3.3.1.
 
 
 
 
In short, when an identifier is scoped, the compiler must try to resolve the identifier. When the scope is a class, the compiler must look up the declaration for the identifier in the outer class. When the outer class hasn't yet been defined, this can't be done and the result is an ill-formed program.