add class to wrap sensitive values

lib/sensitive.rb

@@ -0,0 +1,39 @@
+class Sensitive
+  alias_method :eql?, :==
+  alias_method :equal?, :==
+
+  def initialize(v, ch: "*", head: 2, tail: 2)
+    @v = v
+    @ch = ch
+    @head = head
+    @tail = tail
+  end
+
+  def mask(v)
+    "".concat(v[0, @head], @ch * (v.length - (@head + @tail)), v[-@tail, @tail])
+  end
+
+  def unwrap
+    @v
+  end
+
+  def length
+    @v.length
+  end
+
+  def to_s
+    mask @v
+  end
+
+  def inspect
+    "#<#{self.class.name} @v=#{wrap}>"
+  end
+
+  def hash
+    @v.hash
+  end
+
+  def ==(other)
+    other.is_a?(Sensitive) && other.hash == hash
+  end
+end