Re: Sliding Semantics?

[elroy.jpl.nasa.gov!usc!petunia!nwebre@decwrl.dec.com (Neil Webre)]

In article <1991Jul8.154928.24379@aio.jsc.nasa.gov> dean@sweetpea.jsc.nasa.gov 
writes:
>In article <2871efdf.5c45@polyslo.CalPoly.EDU>, nwebre@polyslo.CalPoly.EDU (Ne
il Webre) writes:
>|> 
>|> There are a couple of workarounds. The best we've been able to invent
>|> has been using type conversions. The substring statement, for instance,
>|> becomes
>|> 
>|>    declare
>|>       type anchor is new string(1..len);
>|>    begin
>|>       s3 := (len, string(anchor(s2.text(posn .. posn + len - 1))));
>|>    end;
>|> 		
>|> That "slides" the index range of the result to be from 1 to some value.
>|> 
>
>Very interesting problem.  I was unable to come a significantly better
>solution.  One question I do have though, is there any advantage to
>using a subtype declaration for anchor, i.e.
>
>    declare
>       subtype anchor is string(1..len);
>    begin
>       s3 := (len, anchor(s2.text(posn .. posn + len - 1)));
>    end;
>
>Will the compiler generate less code in this case since there is no
>type conversion?  This works as desired on the Rational.  Does it do
>the same thing on other machines / other Ada compilers?
>
>--

Good point. Your approach avoids a conversion back to type string.

Neil Webre
Cal Poly, San Luis Obispo, CA
Department of Computer Science