Using type of property key argument's type argument to infer T, and statically check that value type matches.

main.dart

class LayoutBox { }

class RgbColour { }


class LayoutProperty<T>
{
  static final LayoutProperty<LayoutBox> margin = new LayoutProperty<LayoutBox>();

  static final LayoutProperty<RgbColour> colour = new LayoutProperty<RgbColour>();

  static final LayoutProperty<int> gridGap = new LayoutProperty<int>();

  static final List< LayoutProperty<Object> > values = [margin, colour, gridGap];
}

class LayoutStyleModel2
{
  T getProperty<T>(LayoutProperty<T> property)
  {
    T value = null;
    return value;
  }

  void setProperty< T extends LayoutProperty<V>, V>(T property, V value)
  {
    print(property);
    print(value);
  }
}

void main()
{
  LayoutStyleModel2 model = new LayoutStyleModel2();

  model.setProperty(LayoutProperty.margin, LayoutBox.DEFAULT_LAYOUT_BOX);

  // Statically fails, as one expects
  model.setProperty(LayoutProperty.colour, LayoutBox.DEFAULT_LAYOUT_BOX);

  // Statically fails, as one expects
  RgbColour myValue = model.getProperty(LayoutProperty.margin);
}