Problem with "delete" and what about "friend" classes & functions?

[Sean Kelly]

John Kiro wrote:
> Hello
> 
> I have a problem with this statement:
> 
>   delete pDoc.getFile();
> 
> It generates this error:
> 
> "Error: ((cast(CDoc)(pDoc)).getFile)() is not an lvalue"
> 
> The getFile() is a member of CDoc (pDoc is an object of a CDoc
> derived class), and is defined like this:
> 
>   CFile getFile()
>   {
> 	return m_pFile;
>   }
> 
> So any idea about the reason of this error?

Pretend that delete is actually a function declared like this:

     void delete( inout void* val )
     {
         free( val );
         val = null;
     }

rvalues (ie. temporaries) cannot be passed to functions by reference 
because they don't have a concrete address (basically).  So you first 
have to store the result in an lvalue (a normal variable) before calling 
delete on it.

> The code compiles successfully if I replace the delete statement with:
> 
>   CFile tmpFile=pDoc.getFile();
>   delete tmpFile;
> 
> Another point, I guess D doesn't support "friend" classes or
> functions.. wouldn't they be useful sometimes?

They are.  But "friend" as a keyword isn't necessary in D because of the 
way visibility specifiers work.  "private" actually means "visible to 
everything in the current module" and "package" means "visible to 
everything in the current package."  And "protected" means "visible to 
everything in the current module (I think) and to derived classes."  So 
in essence, you can think of all class members as automatically being 
friends with one another.


Sean