def merge_adjacent_strings(arr)
      # Optimize for the common case of one element
      return arr if arr.size < 2
      arr.inject([]) do |a, e|
        if e.is_a?(String)
          if a.last.is_a?(String)
            a.last << e
          else
            a << e.dup
          end
        else
          a << e
        end
        a
      end
    end
def merge_adjacent_strings(arr)
      # Optimize for the common case of one element
      return arr if arr.size < 2
      arr.inject([]) do |a, e|
        if e.is_a?(String)
          if a.last.is_a?(String)
            a.last << e
          else
            a << e.dup
          end
        else
          a << e
        end
        a
      end
    end
Concatenates all strings that are adjacent in an array,
 while leaving other elements as they are.

 @example
   merge_adjacent_strings([1, "foo", "bar", 2, "baz"])
     #=> [1, "foobar", 2, "baz"]
 @param arr [Array]
 @return [Array] The enumerable with strings merged