add Enumerable#each_cons

mrbgems/mruby-enum-ext/mrblib/enum.rb

@@ -82,4 +82,35 @@ module Enumerable
     ary
   end
   
+  ##
+  # call-seq:
+  #   enum.each_cons(n) {...}   ->  nil
+  #
+  # Iterates the given block for each array of consecutive <n>
+  # elements.
+  #
+  # e.g.:
+  #     (1..10).each_cons(3) {|a| p a}
+  #     # outputs below
+  #     [1, 2, 3]
+  #     [2, 3, 4]
+  #     [3, 4, 5]
+  #     [4, 5, 6]
+  #     [5, 6, 7]
+  #     [6, 7, 8]
+  #     [7, 8, 9]
+  #     [8, 9, 10]
+
+  def each_cons(n, &block)
+    raise TypeError, "expected Integer for 1st argument" unless n.kind_of? Integer
+    raise ArgumentError, "invalid size" if n <= 0
+
+    ary = []
+    self.each do |e|
+      ary.shift if ary.size == n
+      ary << e
+      block.call(ary.dup) if ary.size == n
+    end
+  end
+
 end

mrbgems/mruby-enum-ext/test/enum.rb

@@ -23,3 +23,8 @@ assert("Enumerable#take_while") do
   assert_equal a.take_while {|i| i < 3 }, [1, 2]
 end
 
+assert("Enumrable#each_cons") do
+  a = []
+  (1..5).each_cons(3){|e| a << e}
+  assert_equal a, [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
+end