Member template in local class

问题

Given the following code:

 void f()
 {
     class A
     {
         template <typename T>
         void g() {}
     };
 }

g++ 4.4 (and also g++-4.6 -std=gnu++0x) complains: "invalid declaration of member template in local class".

Apparently local classes are not allowed to have template members. What is the purpose of this limitation? Will it be removed in C++0x?

Note: If I make the local class itself a template, rather than giving it a template member:

 void f()
 {
     template <typename T>         
     class A
     {
         void g() {}
     };
 }

I get "error: a template declaration cannot appear at block scope".

回答1:

The purpose of this limitation? Just a guess, but:

• you may use the template class/template member function only within the enclosing function. Therefore you already know all used types within the function and hence can directly specify the used types (for several types, of course, the template variant would have saved some typing).
• although it might not seem so, it is work for all compiler creators and space for bugs and so it must be worth the effort.

Fun Fact: Try to use a local class within a function as a return type for a (c++0x)-lambda function declared in the function: MSVC 2010: internal compiler error ^^.

来源：https://stackoverflow.com/questions/4299314/member-template-in-local-class