Re: Accessing function frame from struct

[Ali Çehreli via Digitalmars-d-learn]

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

Accessing function frame from struct

[Sebastien Alaiwan via Digitalmars-d-learn]

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
  }
}
  }
}