Re: Variant record memory storage question

[Shark8 <onewingedshark@gmail.com>]

On Wednesday, August 1, 2018 at 11:38:06 AM UTC-6, NiGHTS wrote:
> Say I had a variant record like this:
> 
> type Which_One is (Is_Small, Is_Big);
> 
> type Variant_Record (Option : Which_One) is 
> record
>     case Option is
>         when Is_Small =>
>             Var_1 : Byte -- 1 byte
>         when Is_Big =>
>             Var_2 : Some_Large_Record -- 1000 bytes
>     end case;
> end record;
> 
> Will the record Variant_Record( Is_Small ) be stored as 1 byte? Or does it act almost like a C union allocating the memory for Variant_Record( Is_Big ) even though it will never morph at run-time?
> 
> I am trying to determine the most memory-efficient way to store a complex record and it seems Variant_Record can help me do this, but I am unsure if it will work the way I think it will.
> 
> Note I am using gcc. Thank you.

The standard allows for it to be stored as 1-byte, as you desire, but does not require this behavior. Since you are using GCC, I can tell you that it uses the second behavior: because GCC / GNAT views compatibility with C as a very high priority, and also because it's easier to do it that way.

Dmitry, Randy, and/or Simon can probably give you more. (And might have a solution for you.)