code: public static MutableDouble fromExternal(final DoubleSupplier s, final DoubleConsumer c) {
          return new MutableDouble() {
              @Override
              public double getAsDouble() {
                  return s.getAsDouble();
              }
  
              @Override
              public Double get() {
                  return getAsDouble();
              }
  
              @Override
              public MutableDouble set(final double value) {
                  c.accept(value);
                  return this;
              }
          };
      }
docs: Construct a MutableDouble that gets and sets an external value using the provided Supplier and Consumer
  
  e.g.
  <pre>
  {@code
  MutableDouble mutable = MutableDouble.fromExternal(()->!this.value,val->!this.value);
  }
  </pre>
  
  
  @param s Supplier of an external value
  @param c Consumer that sets an external value
  @return MutableDouble that gets / sets an external (mutable) value