还是查了一下，的确是符合标准的。这也灵活得过分了，害得我疑神疑鬼了两天，多亏我还有点道行，伙计们小心了！
http://www.cs.unc.edu/~smithja/C++Nov97/www.cygnus.com/misc/wp/nov97/decl.html#dcl.decl
4 Declarators have the syntax
declarator:
direct-declarator
ptr-operator declarator
direct-declarator:
declarator-id
direct-declarator ( parameter-declaration-clause ) cv-qualifier-seqopt exception-specificationopt
direct-declarator [ constant-expressionopt ]
( declarator )
ptr-operator:
* cv-qualifier-seqopt
&
::opt nested-name-specifier * cv-qualifier-seqopt
cv-qualifier-seq:
cv-qualifier cv-qualifier-seqopt
cv-qualifier:
const
volatile
declarator-id:
id-expression
::opt nested-name-specifieropt type-name
A class-name has special meaning in a declaration of the class of that
name and when qualified by that name using the scope resolution opera-
tor :: (_expr.prim_, _class.ctor_, _class.dtor_).
