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Re: [PATCH 00/30] Read loose references lazily

From
Michael Haggerty <mhagger@alum.mit.edu>
Date
Apr 26, 2012, 21:33 UTC
Message-ID
<4F99BF46.9050501@alum.mit.edu>
In-Reply-To
<xmqqbomfd5bt.fsf@junio.mtv.corp.google.com>
On 04/25/2012 08:39 PM, Junio C Hamano wrote:
Show 12 quoted lines
> mhagger@alum.mit.edu writes:
>
>> From: Michael Haggerty<mhagger@alum.mit.edu>
>>
>> Patches 10 - 25 mostly switch a lot of code from using ref_dir
>> pointers to using ref_entry pointers as arguments and return values.
>> This is important, because ...
>
> The earlier parts looked sane, but the ref_dir set of patches looked
> like merely working around the fact that "struct ref_dir" does not have
> the name field and you had to upcast it to ref_entry to access the full
> name.

Yes, that plus the fact that the ref_entry::flag field is needed in ref_entry (to distinguish between value and directory entries) but also to interpret the contents of the ref_value / ref_dir.

Show 10 quoted lines
> All the places that used to take ref_dir never wanted to get an entry
> that represents a leaf node (i.e. ref_value kind of ref_entry), but now
> because you made everybody to take ref_entry, the resulting code is much
> more error prone and the static type checking done by the compiler helps
> us much less when updating the code.  It can already be seen that you
> had to sprinkle a lot of assert(flag&  REF_DIR), but at runtime in
> non-debug build that will become no-op and it is not a substitute for
> the static type checking we used to have.
>
> Can't we approach this differently so that we can keep the type safety?

Thanks for this comment. I've obviously been ruined by OO languages, in which [name + flag + struct ref_value] and [name + flag + struct ref_dir] (which *are* useful combinations of data) would be subclasses, and the downcasting from ref_entry would only have to occur in only one place, while the compiler could guarantee consistency everywhere else.

In C, I don't see a way to implement the equivalent semantics that is less annoying than the code that I submitted.

But since [name + flag + struct ref_value] and [name + flag + struct ref_dir] never leave the library as structs, it is indeed possible to write the code in a different way that leaves most functions working with ref_dir instead of having to use ref_entry everywhere. I have implemented this and will submit it shortly.

Thanks again for your suggestion; the resulting code is indeed simpler.
Michael
-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/
Previous: Junio C Hamano
Message 37 of 37 in “Read loose references lazily”
  1. 00/30 Read loose references lazilymhagger@alum.mit.edu, Apr 24, 2012
  2. 01/30 get_ref_dir(): return early if directory cannot be readmhagger@alum.mit.edu, Apr 24, 2012
  3. 02/30 get_ref_dir(): use a strbuf to hold refnamemhagger@alum.mit.edu, Apr 24, 2012
  4. 03/30 get_ref_dir(): rename "base" parameter to "dirname"mhagger@alum.mit.edu, Apr 24, 2012
  5. 04/30 get_ref_dir(): require that the dirname argument ends in '/'mhagger@alum.mit.edu, Apr 24, 2012
  6. 05/30 refs.c: extract function search_for_subdir()mhagger@alum.mit.edu, Apr 24, 2012
  7. 06/30 get_ref_dir(): take the containing directory as argumentmhagger@alum.mit.edu, Apr 24, 2012
  8. 07/30 do_for_each_reflog(): return early on errormhagger@alum.mit.edu, Apr 24, 2012
  9. 08/30 do_for_each_reflog(): use a strbuf to hold logfile namemhagger@alum.mit.edu, Apr 24, 2012
  10. 09/30 do_for_each_reflog(): reuse strbuf across recursive function callsmhagger@alum.mit.edu, Apr 24, 2012
  11. 10/30 refs: wrap top-level ref_dirs in ref_entriesmhagger@alum.mit.edu, Apr 24, 2012
  12. Michael HaggertyApr 26, 2012
  13. 11/30 get_packed_refs(): return (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  14. 12/30 get_loose_refs(): return (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  15. 13/30 is_refname_available(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  16. 14/30 find_ref(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  17. 15/30 read_packed_refs(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  18. 16/30 add_ref(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  19. 17/30 find_containing_direntry(): use (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  20. 18/30 get_ref_dir(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  21. 19/30 get_ref_dir(): remove dirname argumentmhagger@alum.mit.edu, Apr 24, 2012
  22. 20/30 search_for_subdir(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  23. 21/30 search_ref_dir(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  24. 22/30 add_entry(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  25. 23/30 do_for_each_ref_in_dirs(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  26. 24/30 do_for_each_ref_in_dir(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  27. 25/30 sort_ref_dir(): take (ref_entry *) instead of (ref_dir *)mhagger@alum.mit.edu, Apr 24, 2012
  28. 26/30 struct ref_dir: store a reference to the enclosing ref_cachemhagger@alum.mit.edu, Apr 24, 2012
  29. 27/30 read_loose_refs(): rename function from get_ref_dir()mhagger@alum.mit.edu, Apr 24, 2012
  30. 28/30 read_loose_refs(): access ref_cache via the ref_dir fieldmhagger@alum.mit.edu, Apr 24, 2012
  31. 29/30 create_dir_entry(): allow the flag value to be passed as an argumentmhagger@alum.mit.edu, Apr 24, 2012
  32. Junio C HamanoApr 25, 2012
  33. Junio C HamanoApr 25, 2012
  34. Michael HaggertyApr 26, 2012
  35. 30/30 refs: read loose references lazilymhagger@alum.mit.edu, Apr 24, 2012
  36. Junio C HamanoApr 25, 2012
  37. Michael HaggertyApr 26, 2012

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