Improve Shotengai::Harray

lib/shotengai/harray.rb

 module Shotengai
   class Harray < Array
     def keys
-      self.map { |obj| obj['key'] || obj[:ket] }
+      self.map { |obj| obj['key'] }
     end
 
     def vals
-      self.map { |obj| obj['key'] || obj[:ket] }
+      self.map { |obj| obj['key'] }
+    end
+
+    def val_at key
+      self.bsearch { |obj| obj['key'].eql?(key) }&.[]('val')
     end
   end
 end
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