anchor.diff:  }
   
   /// A cubic polynomial mapping of the unit interval.
  -class Cubic implements Curve {
  +class Cubic extends Curve {
     const Cubic(this.a, this.b, this.c, this.d);
   
     final double a;
  
positive.code: }
  
  /// An oscillating curve that shrink in magnitude.
  class BounceOutCurve implements Curve {
    const BounceOutCurve();
    double transform(double t) {
      return _bounce(t);
  
negative.code: ///
  /// See [Curves] for a collection of common animation curves.
  abstract class Curve {
    const Curve();
  
    /// Returns the value of the curve at point [t].
    ///
    /// The value of [t] must be between 0.0 and 1.0, inclusive.
    double transform(double t);
  
    /// Returns a new curve that is the reversed inversion of this one.
    /// This is often useful as the reverseCurve of an [Animation].
    Curve get flipped => new FlippedCurve(this);
  }
  
  /// The identity map over the unit interval.
  class Linear extends Curve {
    const Linear();
    double transform(double t) => t;
  }
  
  /// A sawtooth curve that repeats a given number of times over the unit interval.
  class SawTooth extends Curve {
    const SawTooth(this.count);
    final int count;
    double transform(double t) {
  