Resolve #35 with a comment

History.md

@@ -6,6 +6,8 @@
   detection. [#44][]
 - Fixed a theoretical issue reported by Jun Aruga in Diff::LCS::Hunk to raise
   a more useful exception. [#43][]
+- Added documentation that should address custom object issues as reported in
+  [#35][].
 - Fixed more diff errors, in part reported in [#65][].
 
 ## 1.4.3 / 2020-06-29
@@ -271,6 +273,7 @@
 [#29]: https://github.com/halostatue/diff-lcs/pull/29
 [#33]: https://github.com/halostatue/diff-lcs/issues/33
 [#34]: https://github.com/halostatue/diff-lcs/pull/34
+[#35]: https://github.com/halostatue/diff-lcs/issues/35
 [#36]: https://github.com/halostatue/diff-lcs/pull/36
 [#38]: https://github.com/halostatue/diff-lcs/issues/38
 [#43]: https://github.com/halostatue/diff-lcs/issues/43

lib/diff/lcs.rb

@@ -60,6 +60,13 @@ module Diff::LCS # rubocop:disable Style/Documentation
   # +self+ and +other+. See Diff::LCS#lcs.
   #
   #   lcs = seq1.lcs(seq2)
+  #
+  # A note when using objects: Diff::LCS only works properly when each object
+  # can be used as a key in a Hash, which typically means that the objects must
+  # implement Object#eql? in a way that two identical values compare
+  # identically for key purposes. That is:
+  #
+  #   O.new('a').eql?(O.new('a')) == true
   def lcs(other, &block) #:yields self[i] if there are matched subsequences:
     Diff::LCS.lcs(self, other, &block)
   end