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From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Re: Incompatible types for array conversion
Date: Wed, 22 Jul 2015 10:00:35 -0300
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Xref: news.eternal-september.org comp.lang.ada:26982
Date: 2015-07-22T10:00:35-03:00
List-Id: <comp.lang.ada>

On 07/22/2015 02:20 AM, Niklas Holsti wrote:
> On 15-07-22 04:19 , hreba wrote:
>> I have a generic vector package:
>>
>> generic
>>     dim:        positive;
>>     type Real is digits <>;
>> package Vectors is
>>     type Vector is array (1..dim) of Real;
>>     function "*" (a: Vector; b: Real) return Vector;
>> end Vectors;
>>
>> In another package I want to model the definition of a (physical)
>> position vector by its direction and module:
>>
>> package Basic is
>>     type Real is new Interfaces.IEEE_Float_64;
>>     type Length is new Real;
>>
>>     package Positions is new Gen.Vectors (3, Length);
>>     package Directions is new Gen.Vectors (3, Real);
>>
>>     subtype Position is Positions.Vector;
>>     subtype Direction is Directions.Vector;
>>
>>     function "*" (l: Direction; r: Length) return Position;
>> end Basic;
>>
>> Now my attempt to define this function:
>>
>>     function "*" (l: Direction; r: Length) return Position is
>>     begin return Positions."*"(Position(l), r); end "*";
>>
>> gets me the error message in the subject line.
>>
>> Do I have to convert the vector element by element in a loop or is there
>> a more elegant way?
>
> The conversion is rejected because of the conversion condition in RM 4.6
> (24.5/2): "The component subtypes shall statically match". The component
> (sub)types are Real and Length, which are different types, although
> Length is derived from Real. If you change the declaration of Length to be
>
>     subtype Length is Real;
>
> the conversion becomes legal.
>

Thanks a lot for the hint!

-- 
Frank Hrebabetzky		+55 / 48 / 3235 1106
Florianopolis, Brazil