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Input:

template < typename T >
boost::function<void()> f()
{
return []() { typedef typename T::type type; };
}

Output: "typename cannot be used outside a template declaration",
"'T' : is not a class or namespace name"

Input:

template < typename T >
boost::function<void()> f()
{
return []() { typedef T::type type; };
}

Output: "'T' : is not a class or namespace name"

Input:

template < typename T >
struct wtf { typedef typename T::type type; };

template < typename T >
boost::function<void()> f()
{
return []() { typedef typename wtf<T>::type type; };
}

Output: "typename cannot be used outside a template declaration"

Input:

template < typename T >
struct wtf { typedef typename T::type type; };

template < typename T >
boost::function<void()> f()
{
return []() { typedef wtf<T>::type type; };
}

Output: success (assuming T has a type in it)

So the question is, am I doing something wrong or is the compiler just
confused? What of these is correct?


--
http://crazyeddiecpp.blogspot.com/

On 4 Jan., 00:45, Noah Roberts wrote:
> Input:
>
> template < typename T >
> boost::function<void()> f()
> {
> * return []() { typedef typename T::type type; };
> }
>
> Output: *"typename cannot be used outside a template declaration",
> "'T' : is not a class or namespace name"

I also would have expected it to work. G++ 4.5.1 compiles the
following code:

template<class T>
void f() {
[]() { typedef typename T::type type; }();
}

struct foo {
typedef int type;
};

int main() {
f<foo>();
}

So, I guess that (1) you're using the Microsoft Compiler and (2) you
encountered a compiler bug.

Have you tried the following?

template < typename T >
boost::function<void()> f()
{
typedef typename T::type T_type;
return []() { typedef T_type type; };
}


Cheers!
SG