Re: Can I have an array of variant records?

[czgrr <czgrr@my-dejanews.com>]

In article <371DC9BE.585254A6@wbkst21.mach.uni-karlsruhe.de>,
  kobylarz@wbkst21.mach.uni-karlsruhe.de wrote:
> How to alter the discriminant? I searched in several different sources of
> documentation
> and I have not found that.
>
> I declared variant record:
>
> type Tool_Operation(action : Action_Type := Wait) is
>   record
>     case action is
>       when Wait => howlong : time;
>       when Move => where : position; min_time : time;
>     end case;
>   end record;
>
> Let's define variable:
>
>    top : Tool_Operation;
>
> But such statement does not compile:
>
>         top.action := Move;
>
> The compiler returns error: "left hand side of assignment must be a
> variable"
>
> How to alter the discriminant?

The discriminant can not be assigned directly, like the other fields in the
record. In order to assign it, you must also assign every other field in that
variant at the same time, otherwise they would be undefined. Hence, you have
to do something like this...

top :=
  ( action   => Move,
    where    => ...,     -- these are part of
    min_time => ... ) ;  -- the "Move" variant

Changing the discriminant back to "Wait" is a similar process. BTW, that means
that you lose the previous value of "howlong".

czgrr

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They might not even be right. Use at your own risk.

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