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Re: [PATCH v3 01/11] replace: forbid replacing an object with one of a different type

From
Philip Oakley <philipoakley@iee.org>
Date
Sep 1, 2013, 19:26 UTC
Message-ID
<9D27EE89D9994C0997D19E0C0AF7493F@PhilipOakley>
In-Reply-To
<20130901.135321.1182162250658468787.chriscool@tuxfamily.org>
From: "Christian Couder" <chriscool@tuxfamily.org>
Show 30 quoted lines
> From: "Philip Oakley" <philipoakley@iee.org>
>>
>> Sorry for not replying earlier in the series.
>>
>> From: "Christian Couder" <chriscool@tuxfamily.org>
>>> Users replacing an object with one of a different type were not
>>> prevented to do so, even if it was obvious, and stated in the doc,
>>> that bad things would result from doing that.
>>>
>>> To avoid mistakes, it is better to just forbid that though.
>>>
>>> If one object is replaced with one of a different type, the only way
>>> to keep the history valid is to also replace all the other objects
>>> that point to the replaced object.
>>
>> Isn't this a recursion problem? Taken in that order one unravels the
>> whole DAG.
>>
>> However if considered in the reverse direction, one can replace an
>> existing object within the DAG with a carefully crafted alternative 
>> of
>> the same type, but which then wrongly references other dangling
>> objects which are then replaced by objects which have the right type
>> (this last replacement requires -f force).
>
> I am not sure I understand what you are saying.
>
> Anyway in a previous version of this patch I tried to be more explicit
> about this, but Junio basically said that he found no value in
> discussing this more explicitely...
I would agree that it's not worth discussing it more explicitly.

My comment was more about the direction of the line of reasoning which I felt was a bit Catch 22 when starting from an existing complete DAG (no garbage) and attempting to replace an object with another of a different type and still have a valid DAG. The construction of the replacement items needs to be in the right order if one of the replacements is of the 'wrong' type (such a construction requires the creation or uses, and ultimately replacement of, extraneous objects that aren't (yet) in the DAG).

But as already been said that's a problem for the user of the --force option ;-)

Philip
>
> Thanks,
> Christian.
>
Previous: Christian CouderNext: Christian Couder
Message 5 of 33 in “Check replacement object type and minor updates”
  1. 00/11 Check replacement object type and minor updatesChristian Couder, Aug 31, 2013
  2. 01/11 replace: forbid replacing an object with one of a different typeChristian Couder, Aug 31, 2013
  3. Philip OakleyAug 31, 2013
  4. Christian CouderSep 1, 2013
  5. Philip OakleySep 1, 2013
  6. 02/11 Documentation/replace: state that objects must be of the same typeChristian Couder, Aug 31, 2013
  7. 03/11 t6050-replace: test that objects are of the same typeChristian Couder, Aug 31, 2013
  8. 04/11 t6050-replace: add test to clean up all the replace refsChristian Couder, Aug 31, 2013
  9. 05/11 Documentation/replace: add Creating Replacement Objects sectionChristian Couder, Aug 31, 2013
  10. Philip OakleyAug 31, 2013
  11. Christian CouderSep 1, 2013
  12. 06/11 replace: bypass the type check if -f option is usedChristian Couder, Aug 31, 2013
  13. 07/11 Documentation/replace: tell that -f option bypasses the type checkChristian Couder, Aug 31, 2013
  14. Philip OakleyAug 31, 2013
  15. Christian CouderSep 1, 2013
  16. Philip OakleySep 1, 2013
  17. Christian CouderSep 2, 2013
  18. Philip OakleySep 2, 2013
  19. Jonathan NiederSep 2, 2013
  20. Philip OakleySep 2, 2013
  21. Jonathan NiederSep 2, 2013
  22. Philip OakleySep 2, 2013
  23. Christian CouderSep 3, 2013
  24. 08/11 t6050-replace: check that -f option bypasses the type checkChristian Couder, Aug 31, 2013
  25. Eric SunshineSep 1, 2013
  26. Christian CouderSep 1, 2013
  27. 09/11 replace: allow long option namesChristian Couder, Aug 31, 2013
  28. 10/11 Documentation/replace: list long option namesChristian Couder, Aug 31, 2013
  29. 11/11 t6050-replace: use some long option namesChristian Couder, Aug 31, 2013
  30. Philip OakleyAug 31, 2013
  31. Christian CouderSep 1, 2013
  32. Eric SunshineSep 1, 2013
  33. Christian CouderSep 1, 2013

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