🚀 go-pugleaf

In article <1993Jan4.225957.26359@viewlogic.com> sunder@viewlogic.com (Sunder Singhani) writes:
>
>The above IS ambiguous. Explanation follows -

IMHO, there is NO ambiguity.  Sufficient information is available.
 
>-- 4    FUNCTION To_X01  ( b : BIT_VECTOR        ) RETURN  std_logic_vector;
>-- 5    FUNCTION To_X01  ( b : BIT_VECTOR        ) RETURN  std_ulogic_vector;
> 
>Of these you are choosing 4, 5 explicitly by using type qualification -
>ie bit_vector'("00"). 5 returns std_logic_vector and 4 returns std_ulogic_vector.

So far, so good.  Yes, there are two candidates with the same parameter and
result profile.

>The first one when indexed gives you an element of std_ulogic, and the latter
>gives std_logic. Now, std_logic is a subtype of std_ulogic, which implies
>both have the same base type which is std_ulogic. Hence, you end up
>with two interpretations, which is erroneous. The final type qualification

Not so fast.  Just because the parameter/result profiles match doesn't mean
the declaration is ambiguous.  According to LRM 10.5 (The Context of Overload
Resolution) there is a list of rules to be considered along with syntax and
scope/visiblity rules.  The first of these is:

  "1. Any rule that requires a name or expression to have a certain type,
      or to have the same type as another name or expression."

Since this is a constant declaration with a default expression, the following
rule for interface objects (LRM 4.3.3) seems applicable:

  "...The type of a default expression must be that of the corresponding
   interface object."

This narrows the search down to a single choice.  Unless I've missed 
something, Model Technologies appears to be doing the right thing here.

Gary Beihl (gary.beihl@columbiasc.ncr.com)