Re: Practicalities of Ada for app development

[Adam Beneschan <adam@irvine.com>]

On Sunday, June 10, 2012 2:36:46 PM UTC-7, Nomen Nescio wrote:
> "Dmitry A. Kazakov" wrote:
> > 
> > > Please, why have you defined Code_Point as a modular type?
> > 
> > Because code point is unsigned. When you declare something signed
> > you do that because you want negative inverses. Signed integers have
> > the base type with 0 in the middle of its range.
> 
> That's no reason to use mod.  You can put boundaries where you want
> them, integer, or mod.

This isn't quite true because of subtleties of the language.  When you define an  integer "type" with range 0..(2**32-1), the *type* you declare is actually a larger type than that.  It has to be at least -(2**32-1) .. (2**32-1), which is a type that requires 33 bits (in practice, it will probably be 
-2**64 .. 2**64-1).  You then get a subtype with range 0..(2**32-1).  But some calculations have to be done using the base type, which means that using a signed integer type can require some extra conversions, and can require additional processing time on a machine that doesn't have 64-bit arithmetic instructions.  It probably wouldn't matter much if the type is being used to represent a Unicode code point.  But in a more general case, you have to be careful.  It's not really accurate to simply say "you can put boundaries where you want".

IIRC, some people have proposed adding unsigned integer types to the language; they've argued that modular types aren't good enough for some purposes.  But the idea was turned down.

                        -- Adam