Re: Java Risks (Was: Ada News Brief - 96-05-24

[ncohen@watson.ibm.com (Norman H. Cohen)]

In article <Pine.GSO.3.92.960604155403.19912B-100000@nunic.nu.edu>,
Richard Riehle <rriehle@nunic.nu.edu> writes: 

|> >    class C {
|> >       protected: 
|> >          typedef ... T;
|> >          static T x;  // perfectly legal
|> >          struct S {
|> >             T x;      // illegal: protected "member" T inaccessible inside
|> >          } y;         //    a struct, despite nesting.
|> >    }
...
|>                                                 In all honesty, very few
|>   C++ programmers would design a class with such an obviously ugly
|>   profile.

But it's not an ugly profile, it's a perfectly reasonable idiom.  S and T
are strictly part of the implementation of class C, so the programmer
wants to keep them hidden in protected declarations.  The C++ code above
is the direct analog of the following Ada code: 

   package C is

      type C_Type is private;
      ...

   private

      type T is ...;

      type S is
         record
            x: T;   -- T is usable here even though hidden outside
                    --   of package C.
            ...
         end record;

      type C_Type is
         record
            y: S;
            ...
         end record;

   end C;

   package body C is
      ...
      x: T;  -- Corresponds to the C++ static member above, but is hidden
             --    in the package body, where it belongs.
      ...
   end C;

As an aside, here's the latest C/C++ pitfall to bite me: 
*** Error: Mixed metaphor.           ^^^^^^^    ^^^^

     char * six_string_guitar[6] =
        { "E string",
          "A string",
          "D string"
          "G string",
          "B string",
          "E string"
        };

Because of the missing comma following "D string" (did you notice it?),
six_string_guitar is actually quietly initialized to {"E string",
"A string", "D stringG string", "B string", "E string", 0}.  (Adjacent
string constants are concatenated, and default values--zero in the case
of a pointer--are used for missing elements in an initializer.)  What a
language!

--
Norman H. Cohen    ncohen@watson.ibm.com