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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Array slicing question
Date: Mon, 07 Jul 2014 09:04:10 +0100
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Date: 2014-07-07T09:04:10+01:00
List-Id: <comp.lang.ada>

Mike Silva <mjsilva697@gmail.com> writes:

> I (I being an Ada novice) am still fiddling around with writing 4 bits
> of LCD display data into a 32-bit GPIO register.  I have this:
>
>    type Bits_1  is mod 2**1 with Size => 1;
>    type Bits_32x1 is array (0 .. 31) of Bits_1 with Pack, Size => 32;
>    type Bits_8x1 is array (0 .. 7) of Bits_1 with Pack, Size => 8;
>
> and I want to do things like this:
>
>    a32 : Bits_32x1;
>    a8  : Bits_8x1;
> ...
>    a32(4..7) := a8(4..7);
>
> This is not allowed, apparently, because a32 and a8 are different
> types (even though the elements of the arrays are the same type, so
> I'm a little confused, but OK).
>
> So can I do this?  I'm guessing if Bits_32x1 and Bits_8x1 were both
> subtypes of the same type, I could do it - is this correct?  But I
> don't know how to declare such a type, especially given the Pack and
> Size attributes.
>
> I note that (ref confusion above) I CAN do this:
>
>       for i in 4..7 loop
>          gpio32(i) := b8(i);

because the components _are_ the same type.

Would this help?

   type Bits is array (Natural range <>) of Boolean with Pack;

   subtype Bits_32 is Bits (0 .. 31);
   subtype Bits_8 is Bits (0 .. 7);

   A32 : Bits_32 with Size => 32;
   A8 : Bits_8 with Size => 8;

   ...

   A32 (4 .. 7) := A8 (4 .. 7);