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Message-ID: <3DD8C969.D28416F8@ACM.org>
Date: Mon, 18 Nov 2002 11:05:13 +0000
From: Colin Paul Gloster <Colin_Paul_Gloster@ACM.org>
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Subject: Re: Novice help with types and de-allocation.
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The thread starter had:

--snip

package int_buff is
        
        type Int_Buffer is limited private;
--snip
        type Buff_Out is array(Positive range <>) of Integer;

--snip

        function Read_Buff( Y : in Int_Buffer; Read_length : in Natural;
Loc :in Natural) return Buff_Out;
--snip

private

--snip
        type Int_Buffer is array(1..Size) of Integer;
--snip

end int_buff;

package body int_buff is

--snip
        function Read_Buff(Y : in Int_Buffer; Read_Length : in Natural;
Loc : in Natural) return Buff_Out is
        
                Ret_Buff : Buff_Out(1..Read_Length);
        begin
                -- For some reason, the compiler expects Y to be of type
Buff_Out.
                -- Do I need to use Unchecked_Conversion here?
                Ret_Buff := Y(Loc .. Read_Length - 1);
        
                return Ret_Buff;
                
        end Read_Buff;

--snip

end int_buff;

The compiler expects Y to be of type Buff_Out because you are assigning
a slice of Y (all or part of the array Y) to something which is of type
Buff_Out. Buff_Out is also an array of integers, but even if the slice
was the same size as the size of your Buff_Out array, this would be
illegal (arrays which just happen to have the same size in Ada of the
same component types are not the same array array types unless they were
actually declared to be of the same type).

Unchecked_Conversion can be nasty, so can this replacement line:
Ret_Buff := Buff_Out(Y(Loc .. Read_Length - 1));
which is also a conversion. Just make sure it is safe (e.g. that Y(Loc
.. Read_Length - 1) is not longer than Ret_Buff and that if it is
shorter than Ret_Buf, that you are happy with the unfilled in parts
being the way that they are).