Re: [sv-bc] Assignment compatibility of packed arrays of enums

> 2009 makes it legal to create packed arrays of enums.  Is it legal 
> to assign a data object of such a type with a value that is not a 
> packed array of the same kind of enums?

On a previous occasion I have asked similar questions about
packed structs containing enums, which were already legal in 2005.
The consensus seems to be that it is legal:

  typedef enum bit {FALSE, TRUE} boolean;
  struct packed {
    bit [2:0] upper;
    boolean   mid;
    bit [3:0] lower;
  } tripartite = 8'b000_1_0000;
  // effectively copies tripartite.mid=1'b1 !!!!

This has obvious utility in synthesisable design (structured
description of control/status registers, etc) but breaks what
little type checking you otherwise get with enums.  If it's
legal for a packed struct, I can see no reason why it should
not be legal for a packed array.

I am fully aware that any practical language needs to 
have various implicit type coercions, but they sure make
it harder to define and reason about the language.
-- 
Jonathan Bromley
Consultant

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owner-sv-bc@server.eda.org wrote on 02/10/2009 11:17:27:

> From:
> 
> Brad Pierce <Brad.Pierce@synopsys.com>
> 
> To:
> 
> "sv-bc@eda.org" <sv-bc@server.eda.org>
> 
> Date:
> 
> 02/10/2009 11:21
> 
> Subject:
> 
> [sv-bc] Assignment compatibility of packed arrays of enums
> 
> Sent by:
> 
> owner-sv-bc@server.eda.org
> 
> 2009 makes it legal to create packed arrays of enums.  Is it legal 
> to assign a data object of such a type with a value that is not a 
> packed array of the same kind of enums?
> 
> In the following element-by-element assignment, the explicit cast is 
required
> 
> typedef enum logic {FALSE, TRUE} Boolean;
> 
> module test1
> (   input  logic   [5:0] in
> ,   output Boolean [5:0] out
> );
>   for (genvar I = 0; I < 6; I++) begin
>      assign out[I] = Boolean'(in[I]);
>   end
> endmodule
> 
> But are both of the following assignments legal?
> 
> typedef enum logic {STOP, GO} NotBoolean;
> 
> module test2
> (  input  logic      [5:0] in1
> ,  input  NotBoolean [5:0] in2
> ,  output Boolean    [5:0] out1, out2
> );
>   assign out1 = in1;
>   assign out2 = in2;
> endmodule
> 
> 
> -- Brad
> 
> 
> -- 
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> 
> 



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