akr	2016-04-16 00:26:48 +0900 (Sat, 16 Apr 2016)

  New Revision: 54604

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=54604

  Log:
    mention Array#sum with third-party gems.

  Modified files:
    trunk/NEWS
Index: NEWS
===================================================================
--- NEWS	(revision 54603)
+++ NEWS	(revision 54604)
@@ -68,9 +68,15 @@ with all sufficient information, see the https://github.com/ruby/ruby/blob/trunk/NEWS#L68
 
   * Add an into option. [Feature #11191]
 
-=== Stdlib compatibility issues (excluding feature bug fixes)
+=== Compatibility issues (excluding feature bug fixes)
 
-=== Built-in global variables compatibility issues
+* Array#sum is implemented.  Ruby itself has no compatibility problem
+  because Ruby didn't have sum method for arrays before Ruby 2.4.
+  However many third party gems, activesupport, facets, simple_stats, etc,
+  defines sum method.  These implementations are mostly compatible but
+  there are subtle differences.
+  Ruby's sum method should be mostly compatible but it is impossible to
+  be perfectly compatible with all of them.
 
 === C API updates
 

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