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From: ncohen@watson.ibm.com (Norman H. Cohen)
Newsgroups: comp.lang.ada
Subject: Re: Fixed point operator visibility question
Date: 14 Oct 1994 14:42:46 GMT
Organization: IBM T.J. Watson Research Center
Distribution: world
Message-ID: <37m5d6$cp3@watnews1.watson.ibm.com>
References: <00985E28.98D9FB40.9907@iberia.cca.rockwell.com>
Reply-To: ncohen@watson.ibm.com
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Date: 1994-10-14T14:42:46+00:00
List-Id: <comp.lang.ada>

In article <00985E28.98D9FB40.9907@iberia.cca.rockwell.com>,
mlc@iberia.cca.rockwell.com (Michael Cook) writes: 

|> My viewpoint is that fixed point division is defined by package
|> STANDARD, see Ada RM, section 4.5.5, para 9-11.  And so the division
|> should be visible without the 'use' clause.

You are quite right.  See also the last two declarations in Annex C,
paragraph 11.

|> Vendor A's claim is that the example deals with visibility of
|> operations of derived types.  The argument is that Fixed_Type is
|> a derived type of an anonymous predefined fixed point type (RM
|> 3.5.9 para 9).
|>
|> The derived type introduces a derived "/" operator, that hides the
|> predefined "/" operator in the scope of the declaration of Fixed_Type
|> (RM 3.4 para 5).

Vendor A is wrong.  The "/" operator in question is not an operation of
the parent fixed-point type.  Rather, it is a "magic" operation that
takes operands of ANY fixed-point type and produces a result of type
universal_fixed.  Thus it is not inherited.

|> package Fixed_Type_Example is
|>
|>    Fixed_Type_Delta : constant := 1.0 / (2.0 ** 27);
|>
|>    type Fixed_Type is delta Fixed_Type_Delta range -16.0 .. 16.0;
|>
|> end Fixed_Type_Example;
|>
|> -------------------------
|>
|> with Fixed_Type_Example;
...
|>    type Value_Type is range -2**15 .. 2**15 - 1;
...
|>       H   : Fixed_Type_Example.Fixed_Type;
|>       PH  : Fixed_Type_Example.Fixed_Type;
|>
|>       PCV : Value_Type;
...
|>       PCV := Value_Type (H / PH);

--
Norman H. Cohen    ncohen@watson.ibm.com