• Sebastien Alaiwan (36/36) Jun 25 2017 Hi guys,
• =?UTF-8?Q?Ali_=c3=87ehreli?= (47/83) Jun 26 2017 I don't know why the asymmetry but that's how it is but the following

Sebastien Alaiwan <ace17 free.fr> writes:

Hi guys,
here's my full code below.
My problem is that last "auto Y = X" assignment, that the 
compiler won't accept:

yo.globalFunction.DirectStruct.IndirectStruct.indirectMemberFunc 
cannot access frame of function yo.globalFunction

I was expecting X to be accessible from here.
Suprisingly, if I replace all "struct" with "class", the last 
assignment is accepted by the compiler.
Could someone please tell me why the scoping asymmetry between 
structs and classes?

void globalFunction()
{
   auto X = 0;

   struct DirectStruct
   {
     void directMemberFunc()
     {
       auto Y = X; // OK, X is accessible

       struct HybridStruct
       {
         void hybridFunc()
         {
           auto Y = X; // OK, X is accessible
         }
       }
     }

     struct IndirectStruct
     {
       void indirectMemberFunc()
       {
         auto Y = X; // Error: can't access frame of globalFunc
       }
     }
   }
}

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 06/25/2017 06:01 AM, Sebastien Alaiwan wrote:
 Hi guys,
 here's my full code below.
 My problem is that last "auto Y = X" assignment, that the compiler won't
 accept:

 yo.globalFunction.DirectStruct.IndirectStruct.indirectMemberFunc cannot
 access frame of function yo.globalFunction

 I was expecting X to be accessible from here.
 Suprisingly, if I replace all "struct" with "class", the last assignment
 is accepted by the compiler.
 Could someone please tell me why the scoping asymmetry between structs
 and classes?

I don't know why the asymmetry but that's how it is but the following 
explanation would be acceptable to me.

 void globalFunction()
 {
   auto X = 0;

   struct DirectStruct
   {
     void directMemberFunc()
     {
       auto Y = X; // OK, X is accessible

       struct HybridStruct
       {
         void hybridFunc()
         {
           auto Y = X; // OK, X is accessible
         }
       }
     }

     struct IndirectStruct
     {
       void indirectMemberFunc()
       {
         auto Y = X; // Error: can't access frame of globalFunc
       }
     }
   }
 }

IndirectStruct is not a nested struct; rather, just a type defined 
inside DirectStruct. So, anybody can simply use it on its own without a 
DirectStruct object around. (Yes, there is a name-access issue in this 
example but it doesn't change the fact that IndirectStruct is just a 
type defined by DirectStruct.)

Commenting out the offending line and returning an IndirectStruct:

auto globalFunction()
{
   auto X = 0;

   struct DirectStruct
   {
     void directMemberFunc()
     {
       auto Y = X; // OK, X is accessible

       struct HybridStruct
       {
         void hybridFunc()
         {
           auto Y = X; // OK, X is accessible
         }
       }
     }

     struct IndirectStruct
     {
       void indirectMemberFunc()
       {
           // Commenting out...
         // auto Y = X; // Error: can't access frame of globalFunc
       }
     }
   }

   // Making and returning an IndirectStruct without any associated
   // DirectStruct as its outer object:
   return DirectStruct.IndirectStruct();
}

void main() {
     auto a = globalFunction();

     // Able to use an IndirectStruct directly:
     a.indirectMemberFunc();
}

On the other hand, HybridStruct is a nested struct because it does have 
an outer scope: the body of directMemberFunc(). Again, I don't know why 
classes are different.

Ali