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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Incompatible types for array conversion
Date: Wed, 22 Jul 2015 10:41:20 +0300
Organization: Tidorum Ltd
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Date: 2015-07-22T10:41:20+03:00
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On 15-07-22 10:13 , Simon Wright wrote:
> Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>
>> 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.
>
> I tried
>
>     generic
>        dim:		positive;
>        type Real is digits <>;
>     package Vectors is
>        type Vector is array (1..dim) of Real'Base;
>
> but it still failed. (GPL 2015, FSF 5.1.0)

Did you expect it to work? Real'Base gets rid of any constraints on 
Real, but AIUI does not get rid of the type derivation; if "type Length 
is new Real", Length'Base is not the same as Real'Base -- the "new" 
makes them different.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .