Re: Teaching new tricks to an old dog (C++ -->Ada)

[Pascal Obry <pascal@obry.org>]

"Hans Malherbe" <hans.malherbe@gmail.com> writes:

> This looks like a limitation, but I'm not sure I understand correctly.

Agreed. All this is somehow limiting. That's the trade off for the
safetly. But when you are used to it, this limitations are not so bad, and
quickly you can't live without them.

> Example please!
> 
> A few other questions:
> 
> Do you have nested functions like Pascal have?

Yes.

> Can you access local variables?

Of course yes. Otherwise what would local variables will be useful for?

> Can you pass pointers to these functions around?

Around no! The rules are strict here.

This case is ok, P1 same level as PA.

<<
procedure Demo is

   type PA is access procedure;

   procedure P (Proc : in PA) is
   begin
      null;
   end P;

   procedure P1 is
   begin
      null;
   end P1;

   procedure P2 is
   begin
      P (P1'Access);
   end P2;

begin
   null;
end Demo;
>>

This is not ok, P3 deeper than PA.

<<
procedure Demo is

   type PA is access procedure;

   procedure P (Proc : in PA) is
   begin
      null;
   end P;

   procedure P1 is
   begin
      null;
   end P1;

   procedure P2 is
      procedure P3 is
      begin
         null;
      end P3;
   begin
      P (P3'Access);
   end P2;

begin
   null;
end Demo;
>>

Here is what GNAT reports for example:

   $ gnatmake demo
   gcc -c demo.adb
   demo.adb:22:10: subprogram must not be deeper than access type
   gnatmake: "demo.adb" compilation error

No dangling pointers.

> Can you pass non-type parameters (like the number 3.14) to templates?

Yes. We can pass types, packages, procedure, functions, variables and
constants.

> Can templates recurse?

Yes.

> Can you program "const correct"? Eg. if you declare a member function
> as const the compiler will help you not mutate the object or call any
> functions that do. Also, if you pass a parameter as a const reference,
> you will not be able to mutate the object the parameter references.

Not sure to understand everything. But yes, if you have:

   Value : constant String := "whatever";

It will never be able to mutate Value.

Pascal.

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