Re: Ada Advocacy.

[Dave Thompson <david.thompson1@worldnet.att.net>]

On Tue, 26 Aug 2003 22:20:36 +0100, "Luke A. Guest"
<laguest@__n_o_s_p_a_m__abyss2.demon.co.uk> wrote:
<snip>
> Not an URL, but something that I and other programmers have always wanted
> to do in C/C++/etc. but cannot is the printing of names of variables ;-)
> 
> That's a damn nice debugging feature. It's been a while but I think it's
> something like
> 
> declare
> 	test : Integer := 5;
> begin
> 	-- I'm really unsure about the overloaded + operator here, like I said
> 	-- it's been a while (around 6 years!)
> 	Write test'Name + " = " + test;
> end
> 
Put[_Line] and test'Image.

> should send "test = 5" to the console.
> 
> Something like that anyway ;-P Try doing that in C/C++ without a lookup
> table :-(
> 
Generating the string label is easy enough in C or C++ using the
preprocessor # (stringize) operator -- as well as just writing it out
by hand for a fixed value.  But the value conversion in C must be
coded knowing the data type, e.g.:
#define STR(x) #x
... printf (STR(test) " = " "%d" "\n", test ); /* for an int */
/* but %ld for long int, %f for a float or double, etc. */
/* and this doesn't work at all for non-builtin types */

In C++ all builtin types have operator<< predefined, and you can
define it yourself for class types (and enums, although those can also
default to builtin integers), in which case this always works:
... cout << STR(test) << " = " << test << endl;

and can be generated automatically from one variable name like:
#define PRINTVAR(x) cout << # x << " = " x << endl;
... PRINTVAR(test)

These can also be modified in obvious ways to do other things than
stdout, like C sprintf to a buffer or C++ << to a stringstream,
display in a GUI messagebox, send via RPC or CORBA, etc.

PL/I has a builtin facility to output any variable(s), or all, with
names -- PUT DATA -- but cannot be used for any other purpose.
Fortran has NAMELIST I/O to do the same thing for pre-chosen groups of
variables, which works bit is a bit clumsy for just one.

> Another thing that's really useful is being able to declare the range of,
> say, an integer variable - and with bounds checking it gets caught at
> compile & runtime (depending on whether it's accessed with a constant or
> not).
> 
Pascal also does this.  C++ doesn't for builtin integer types, but you
can write an integer-like class which does, or better a template which
generates such (lightweight) classes on demand.  Similarly subscripts
are not checked for builtin arrays, but can be for stdlib containers
like std::vector and for array-like classes that you write or generate
from a template.

> The only downside to Ada is the amount of work that has to go into a
> simple program just to dump out some text (not very good for beginners) to
> the console.
> 
> Also meaningful names negates the need for the absolutely disgusting
> hungarian notation.
> 
This is equally true of all languages above (and most if not all
others) for user names.  Although the names in the Ada standard
library(s) are with perhaps a few exceptions more meaningfully (and
consistently) chosen than in pretty much all other common languages.

- David.Thompson1 at worldnet.att.net