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Why does a struct have to be in the same namespace as a template class in order to compile?


Why does a struct have to be in the same namespace as a template class in order to compile?

By : user2954663
Date : November 22 2020, 10:31 AM
around this issue It's not about the struct.
It's about bind and Argument Dependent Lookup.
code :


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Specialization of 'template<class _Tp> struct std::less' in different namespace

Specialization of 'template<class _Tp> struct std::less' in different namespace


By : user1772460
Date : March 29 2020, 07:55 AM
Does that help This is still the way to do it. Unfortunately you cannot declare or define functions within a namespace like you would do with a class: you need to actually wrap them in a namespace block.
Template class Y in namespace X with class X can't compile in VS2010

Template class Y in namespace X with class X can't compile in VS2010


By : Silvana Olteanu
Date : March 29 2020, 07:55 AM
Hope this helps It is a compiler bug. If you will define the constructor the following way
code :
template<typename type>
::A::B<type>::B()
{
}
forward declaration of a class template including a namespace causes compile-error

forward declaration of a class template including a namespace causes compile-error


By : Lou Seq
Date : March 29 2020, 07:55 AM
Hope this helps Yes, this is a bug.
According to [dcl.type.elab]/1,
code :
namespace N {
    struct S;
}
struct N::S; // error: forward declaration of struct cannot have a nested name specifier
C++ Template function fails to compile with g++ when using namespace

C++ Template function fails to compile with g++ when using namespace


By : user1064356
Date : March 29 2020, 07:55 AM
it fixes the issue The following code compiles just fine: (Without namespace) , In the code:
code :
template <class T>
void foo(const int & from, std::vector<T> & to)
{
    T bar;
    foo(from, bar);
multi inheriting a struct from struct and template struct, ordering matters when accessing base non-template struct data

multi inheriting a struct from struct and template struct, ordering matters when accessing base non-template struct data


By : user2160133
Date : March 29 2020, 07:55 AM
wish of those help , Hm, I think I see where the problem lies:
code :
struct D : B<D>, A { };
struct D
{
    B<D> implicitly_inherited_B_D;
    A    implicitly_inherited_A;
};
D* d    = new D();
void* v = d;
A* a    = static_cast<A*>(v);
D* d    = new D();
void* v = &d->implicitly_inherited_B_D;
A* a    = static_cast<A*>(v);
// or equivalent:
A* aa   = reinterpret_cast<A*>(&d->implicitly_inherited_B_D);
D* d    = new D();
void* v = static_cast<A*>(d);
// now this will work fine (v points to D's A part):
A* a    = static_cast<A*>(v);
D* dd   = static_cast<D*>(a); // even this one, original object was constructed as D
D* d  = new D();
A* a  = d;
D* ds = static_cast<D*>(a);
D* dr = reinterpret_cast<D*>(a); // actually undefined behaviour!!!

std::cout << d << std::endl << a << std::endl << ds << std::endl << dr << std::endl;
10001000
10001008
10001000
10001008
void* v = d; // -> need to go back via static_cast<D*>!

A* a    = static_cast<A*>(v);    // requires v = static_cast<A*>(d);
B<D>* d = static_cast<B<D>*>(v); // requires v = static_cast<B<D>*>(d);
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