Re: [vhdl-200x] VHDL 2008 : std_logic_textio package

On 15 Sep 2013, at 8:16 AM, chuck and teril swart <chuckterilswart@gmail.com> wrote:

> In my opinion, the best solution, and the one most compatible with existing implementations is to
> change the default library declarations in 13.2 to read something like:
> 
> "Every design unit except a context declaration and package STANDARD is assumed to contain the following implicit context items as part of its context clause:
> 
> library STD, WORK, IEEE; use STD.STANDARD.all;"
> 
> Are there problems with this solution? Maybe. First, will package std_logic_1164 compile? Its the first package in library IEEE and maybe library IEEE doesn't exist until after this package compiles. I don't think that this is a real problem.


As long as you didn't also include implicit use clauses for packages found in library IEEE,  that would work.  ( "a)  A potentially visible declaration is not made directly visible if the place considered is within the immediate scope of a homograph of the declaration", preventing things like changing type and subtype declarations as done for std_logic_vector in 2008, possibly precluding developing new versions of packages by other than tool vendors).

Personally I see this as a defect in the description provided by the std_logic_textio package declaration introduced as the result of the 2008 changes to package std_logic_1164, specifically adding various flavors of READ, WRITE, HREAD, HWRITE, OREAD and OWRITE instead of placing those in the  package std_logic_textio.

std_logic_textio is simply missing a library clause for library IEEE.  The package declaration for std_logic_textio has no meaning other than providing backward compatibility and should have contained the library clause making library logical name IEEE visible.

Adding additional an additional implicit context item seems the wrong solution. It defeats the purpose in having the library logical name IEEE made visible if there are no dependencies on it being visible other than for purposes of avoiding correcting the text of the std_logic_textio package declaration.  You could as easily argue that the packages found in library IEEE should be moved to library STD.













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