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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Porting ADA source
References: <40FBBB16.8050206@noplace.com>
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Date: 2004-07-19T18:46:31+00:00
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>if Ada had some kind of conditional compilation directive -
>but since those are viewed as "Morally Evil"
  Not "Morally Evil", just "Generally A Poor Solution".
In in the current OP's situation, he can use "renames" for his
differently named library packages/routines, representation clauses
to be explicit about layout of data structures, and problem-oriented,
rather than (obsolete) hardware-oriented types to specify the sizes
of integers, floats, etc.  ie, which is better:

#ifdef Alpha
  Y := Cosine(X);
#else
  Y := Cos(X);
#endif

vs
  function Cosine(X : Float) return Float renames Cos;
  ...
  Y := Cosine(X); -- original, unchanged, source

---------

#ifdef Alpha
  Accuracy,
  Distance_In_Centimeters : Integer; -- DEC Alpha 64 bits
#else
  Accuracy,
  Distance_In_Centimeters : Long_Integer; -- pc 64 bits
#endif

vs:

  type Accurate_Type is range -2**63 .. 2**63-1;
  -- global search and replace changes "Integer" to "Accurate_Type" ?
  Accuracy,
  Distance_In_Centimeters : Accurate_Type;

---------

In the case of structures for interprogram communication, of which
there typically aren't all that many, there's no way to avoid a rep
clause, even if conditional compilation was available.

  type Complicated_Structure_Type is record
    I,J : Accurate_Type;
    Flag: Boolean;
    X : Rough_Float;
    Y : Accurate_Float;
  end record;
-- added explicit representation clause
  for Complicated_Structure_Type use record -- be explicit
    I at 0 range 0 .. 63;
    J at 8 range 0 .. 63;
    Flag at 16 range 0 .. 7;
    X at 24 range 0 .. 31;
    Y at 28 range 0 .. 63;
  end record;