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From "Kim Jin Chul (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-5116: Remove deprecated hash * types in gutil
Date Fri, 14 Jul 2017 01:47:11 GMT
Kim Jin Chul has posted comments on this change.

Change subject: IMPALA-5116: Remove deprecated hash_* types in gutil
......................................................................


Patch Set 3:

(2 comments)

http://gerrit.cloudera.org:8080/#/c/7414/3/be/src/gutil/hash/hash.h
File be/src/gutil/hash/hash.h:

PS3, Line 218: 
As I told in the previous comment, _gnu_ctx is replaced into std.

https://gerrit.cloudera.org/#/c/7414/1/be/src/gutil/hash/hash.h@a278


Line 251
You may know std already defined pointer type as below.

   /// Partial specializations for pointer types.
   template<typename _Tp>
     struct hash<_Tp*> : public __hash_base<size_t, _Tp*>
     {
       size_t
       operator()(_Tp* __p) const noexcept
       { return reinterpret_cast<size_t>(__p); }
     };

I guess your hash function is more faster than std's implementation, but there are pros and
cons. I found the interesting article: https://stackoverflow.com/questions/20953390/what-is-the-fastest-hash-function-for-pointers

I have the following issue on this. Please answer it.

How to implement a customized hash specialization for pointer type.
I removed your code because it cannot be redefined. I think we need to introduce a new template
class which extends std::hash<T> if we want to keep own hash.


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Gerrit-MessageType: comment
Gerrit-Change-Id: I06af30fd15acd43a60e3c30af54056c96520b6e9
Gerrit-PatchSet: 3
Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-Owner: Kim Jin Chul <jinchul@gmail.com>
Gerrit-Reviewer: Jim Apple <jbapple-impala@apache.org>
Gerrit-Reviewer: Kim Jin Chul <jinchul@gmail.com>
Gerrit-HasComments: Yes

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