RE: [vhdl-200x] Closely related record types

Hi,

I prefer cautious changes to language semantics.  Therefore I vote for
option 3.  

This is unlikely to lead to accidental errors, and it deals with the most
common cause of irritation, which is that copy-and-paste can produce a
different data type.

Maybe there should be an explicit declaration of 'closely-related' for cases
1 and 2.

Regards,

Peter.


-----Original Message-----
From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org] On Behalf Of
ryan.w.hinton@L-3com.com
Sent: 29 November 2012 17:40
To: vhdl-200x@eda.org
Subject: [vhdl-200x] Closely related record types

All:

I finished the first cut for a closely-related record types proposal.  

http://www.eda-twiki.org/cgi-bin/view.cgi/P1076/RelatedRecords

There is one remaining item to be decided since there are several possible
rules for declaring two record types closely related.

1. Match record elements by name.
2. Match record elements by position.
3. Match record elements by name and position. 

Here is some arguments for/against copied from the TWiki page.

Rule 3 is the most restrictive and least ambiguous. In other words, it's the
safest. And it satisfies my current needs, so I'm content with it.
But it's also the most likely to not be useful in "obvious" cases.

Rule 2 is similar to the array rule. Array elements are converted by
position. But array indices don't usually convey information like record
element names. (The exceptions are the new fixed- and floating-point
packages, but they have to jump through some hoops to avoid issues with
VHDL's willingness to switch bounds and directions on array dimensions.)
Also, array elements are homogeneous while record elements typically are
not.

Rule 1 uses the element names, which typically represent the designer's
intent. However, naming is rarely unique (coming up with good names is often
hard), so variations are likely. This is my favorite option.

Opinions?  Feel free to edit the page or respond via email.  I'll try to
collect any good ideas from the reflector back to the proposal page.

---
Ryan Hinton
L-3 Communications / Communication Systems West ryan.w.hinton@L-3com.com
 


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