Re: some questions re. Ada/GNAT from a C++/GCC user

[bobduff@world.std.com (Robert A Duff)]

[Removed from comp.lang.c++, since I fear C++ folks are bored of this.]

In article <4jrhj0$lqd@tpd.dsccc.com>,
Kevin Cline <kcline@sun132.spd.dsccc.com> wrote:
>This is a flaw in the Ada language design, IMHO.  Why should
>different methods be used to externalize primitive and user-defined types?
>It certainly makes program maintainence more difficult; imagine a change
>from
>
>	type sequence_number_type is 0..2**32-1
>
>to
>
>	type sequence_number_type is 
>	record
>	  time: time_type;
>	  serial: 2**32-1;
>	end;
>
>If this change was not anticipated then every use of 'IMAGE to
>output a sequence number must be changed to IMAGE().

I suppose.  But you'll also have to change other stuff, like any numeric
literals, and any arrays indexed by sequence_number_type, and any
case_statements, which aren't legal when you change it to a record.
This is a much more general issue -- some prefer a language like Lisp,
which uses the same syntax for just about everything.

If Sequence_Number_Type is really an abstract data type, you'll probably
make it a private type in the first place, and then you won't have to
change anything outside the package.

Actually, I generally do *not* use Integer'Image directly -- I use a
function called Image, even for Integer types, and I use type derivation
to inherit it.  Partly for the reason you stated.  Also, Integer'Image
has an annoying habit of putting an extra unwanted blank, plus it
doesn't work for hexadecimal, and various other formatting options I
like to have.

>>The "&" operator just concatenates Strings.  So to
>>print out some stuff, you write:
>>
>>    Put("X = " & Integer'Image(X) & "; and List = " & Image(List));
>
>Sloshing all those characters around unnecessarily gets a bit
>expensive after a while.  This expression is likely to copy the list
>image twice before it is actually output.

True.  We were talking about debugging printouts, so it doesn't matter
in that context.  In a context where it *does* matter, you can call Put
once for each string.  Also, in Ada, you can define operators, so you
can play the same games as C++ does with "<<" and ">>", although you
have to use "&" or something as the operator name.  I've never done
that, because it seems ugly to me -- a matter of taste, I suppose.

- Bob