Use StringIO#truncate

Author: mrkn

example/animation.rb

@@ -12,7 +12,7 @@ def out.tty?; true; end
 Signal.trap(:INT) { continue = false }
 
 while continue
-  out.string = ""
+  out.truncate(0)
 
   xs = 0...N
   ys = xs.map {|x| Math.sin(2*Math::PI*(x + shift) / N) }