Re: Array Help?

[stefan-lucks@see-the.signature]

On Wed, 7 Mar 2012, Randy Brukardt wrote:

> "Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
> news:wccy5rls0hl.fsf@shell01.TheWorld.com...
> > stefan-lucks@see-the.signature writes:
> >>   procedure Sort(Items: in out array(generic Positive range <>) of T) is
> >
> > Interesting idea.
> 
> Can't you do this with a type conversion to an appropriate constrained array 
> subtype? (Such conversions slide.) I suppose it could be a pain to declare 
> such a subtype in front of every call, but it is a trick I've used a some 
> cases (usually in wrappers) to force sliding on arguments.

Can you explain a bit more?

> I suppose a more convinient way to force that would be helpful.

Beyond the inconvenience, there are two further issues: 

1. Testing

When you declare 

  procedure Sort(Items: in out array(Positive range <>) of T)

in a package specification, and you try to write a proper black-box test, 
you need *more* test cases then when you do the same with another popular 
language. One of the additional test cases could look like 

  declare
    X: array (Positive range Positive'last-2 .. Positive'Last) := ...;
    Y: array (Positive range Positive'last-2 .. Positive'Last) := ...; 
  begin
    Sort(X);
    Assert(X=Y);
  end;

Some time ago, I have actually been bitten by forgetting such a test case. 

So the sad reality is that there is a property where Ada makes testing 
harder than, say, C or C++.  


2. Generality

Given the (Ada 2020?) specification

  procedure Sort(Items: in out array(generic Positive range <>) of T);

Sort(X) should be callable if the index type of X is any discrete type, 
except when the index type is too large (i.e., X has more than 
Positive'Last elements). 


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