Re: [vhdl-200x] VHDL-2008: Records and aggregates

On 10/04/15 18:32, Jim Lewis wrote:
> Hi,
> I just ran into an interesting issue with VHDL-2008 aggregates.  In
> VHDL-2008, we allowed aggregates to effectively do concatenation when
> the target is an array.
>
> Unfortunately this means you have a to_string function that is
> overloaded to handle records, it is now ambiguous since the record
> aggregate can also be interpreted as std_logic_vector.
>
>        write (buf,  to_string( (UartRxRec.Data, UartRxRec.ErrorMode) )) ;

No, this is ambiguous since VHDL 87, as the type of an aggregate is
determined by the context.

> If you use named aggregates, this is not an impact.  However, if you do
> not, it may be a significant impact.

No, that's not correct.  Use of association by name has no impact for
determining the type.

Tristan.

> Hence, now you have to add a type qualifier.  This is an unfortunate
> side-effect.
>        write (buf,  to_string( UartStimType'(UartRxRec.Data,
> UartRxRec.ErrorMode) )) ;
>
> The original change was targeted at handling situations like:
>    (CarryOut, Sum_unsigned) <= ('0' & A_unsigned) + B_unsigned ;
>
> And also handles situations like:
>    (ExtraBit, Accumulate_ufixed) <= Accumulate_ufixed + A_ufixed ;
>
> Really wish we had allowed concatenation on the LHS instead.
>
> We may need to look into how big of an impact this causes.
>
> Jim
>


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