[vhdl-200x-ft] Should ?? be implicit or explicit

Folks,

In FT18, we decided that the declarations of "??" for BIT and STD_ULOGIC be
explicit declarations, not implicit declarations.  I don't recall the
rationale, and am not sure there is a good one.

The only difference I can see between the two choices is in what would
happen if a user were to declare an overload for "??" for BIT or STD_ULOGIC
in a separate package, and then use that package as well as STANDARD or
STD_LOGIC_1164.  In that case,

- with an explicit declaration of the predefined operator, neither version
would be directly visible in the user's design unit

- with an implicit declaration of the predefined operator, the predefined
declaration would not be directly visible and the user's explicit
declaration would be directly visible.

Apart from "??", all predefined operators in STANDARD are implicitly
declared.  Making "??" explicitly declared introduces an inconsistency.  Is
there a good rationale to do so?

Cheers,

PA

--
Dr. Peter J. Ashenden                        peter@ashenden.com.au
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