Re: Ada The Best Language?

["Marc A. Criley" <mcqada@earthlink.net>]

Bertrand Augereau wrote:
> 
   --> (Reinserted from my original response...)
> > Consider this:
> > 
> >    type Altitude is range 0 .. 50_000;
> >    Above_Ground : Altitude;
> > 
> > The "defensive" interpretation says that you can now be assured an
> > attempt to assign a negative altitude or go into military airspace will
> > be immediately caught.
   <--
> > 
> > But look at what you get from the "informational" interpretation:
> >   'First, 'Last, 'Size, 'Range, 'Address, 'Min, 'Max, 'Image, 'Val,
> > 'Pos, 'Value, 'Input, 'Output, 'Read, 'Write, 'Pred, 'Succ, 'Valid,
> > 'Wide_Image, 'Wide_Value, 'Wide_Width, 'Width.
> 
> C++ traits address quite nicely this issue.

This is odd, having spent the last couple years immersed in C++ projects
with very experienced C++ programmers (including co-authoring a C++
Programming Practices standard), I've never encountered anyone
suggesting their use, much less employing them.

Doing a Google search on "C++ traits" brought up only a handful of
relevant entries, the contents of which described it more as a
"technique" than a language feature--and a technique available only to
templates at that.  (Though I may be misinformed regarding this aspect,
I'm going by how traits were presented in the various references.)

The only reference to something like traits in the MSVC++ Help Index was
a "traits_type" data member. Digging further, that did lead to the
discovery of MSVC++ supporting the traits technique, though as noted
above, only for specific template classes.

And not a single one of my C++ books, including "The ANSI/ISO C++
Professional Programmer's Handbook", published in 1999, has an index
entry for "traits".


While C++ type traits may be a technique to extract type information,
its applicability appears limited, and is certainly not available to
range constrained scalar type definitions.  The use of the technique for
other than predefined classes (such as basic_string instantiated with
char) appears to require the _developer_ implement the functionality of
each trait.

Hardly comparable to Ada automatically providing all this information
extraction functionality as part of its standard definition.

Marc A. Criley
Senior Staff Engineer
Quadrus Corporation
www.quadruscorp.com