what about using a static class with static properties returning new instances of concrete classes extending an abstract one

MyObject has a shape and the shape have to be chosen and passed as argument to the ctor, can't exist a MyObject whitout a shape and the shape can't vary along his life. It happens often in real life.

namespace JackNova.ConsoleClient.Test.Fun
{
abstract class Shape { }

class Circle : Shape { }
class Square : Shape { }
class Triangle : Shape { }

static class Shapes
{
    public static Circle Circle { get { return new Circle(); } }
    public static Square Square { get { return new Square(); } }
    public static Triangle Triangle { get { return new Triangle(); } }
}

class MyObject
{
    public Shape Shape { get; private set; }

    public MyObject(Shape shape)
    {
        this.Shape = shape;
    }

}

class Test
{
    static void Run()
    {
        MyObject coolOne = new MyObject(Shapes.Circle);
    }
}
}

I think I'm violating some principle here, the open closed one for example. My purpose is to simplify developing at design time. As you can see when I instanciate MyObject I don't have to remeber wich kind of objects I can pass as argument but they are instanciated and passed by the abstract class.

Do you thi开发者_如何学JAVAnk this sucks?

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It's fine to have an abstract class and a class which takes a reference to an instance of that abstract class in the constructor and sets an effectively-readonly property.

I would question your use of properties in the static class though:

• How do you benefit in usage over just calling new Circle()?
• If there were a benefit, I think it would still make sense to make these methods instead of properties.

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I believe what you are trying to do should be a function of the tool. For example, Visual Studio's IntelliSense would tell you the valid types that can be passed into MyObject.

Also, properties should generally not have any side-effects. So the Circle property should really be a CreateCircle method (or something similar).

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I don't know if it violates a principle, but I really like the readability and expressivity of this syntax.

If you consider that shapes are value objects, does it matter that much that each call to Shapes.Circle creates a new Circle ?