关于c＃：在相关的类层次结构中实现工厂方法

Implementation of factory method in related class hierarchies

请参见代码：

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class X
{
public string x;
}

class Y : X
{
public string y;
}

class A
{
string a;
public virtual X createX<T>()
where T : X, new()
{
return new T() { x = a };
}
}

class B : A
{
string b;
public override X createX<T>()
{
var x = base.createX<T>();
if (x is Y)
((Y)x).y = b; // Yak.
return y;
}
}

...
var c = new B();
var z = c.createX<Y>(); // Yak. I prefer to not needing to know the type Y

我不喜欢这段代码，试图想出更好的方法来重构它。一般的想法很简单，层次结构的每个类都有工厂方法来生成镜像层次结构对应类的实例。我得到一个根类或派生类的实例，需要返回对应类或其派生类的实例(作为根对应类)。我有什么想法或者设计模式可以代替吗？

相关讨论

这是你想要的吗？

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class BaseProduct
{
public string x;
}

class ChildProduct : BaseProduct
{
public string y;
}

class BaseFactory
{
string a;
public virtual BaseProduct buildProduct(BaseProduct product = null)
{
if (product == null)
product = new BaseProduct();

product.x = a;
return product;
}
}

class ChildFactory : BaseFactory
{
string b;
public override BaseProduct buildProduct(BaseProduct product = null)
{
if (product == null)
product = new ChildProduct();
//else if (!(product is ChildProduct))
// return null or throw exception

((ChildProduct)product).y = b;
return base.buildProduct(product); //build BaseProduct.x
}
}

...
var cFactory = new ChildFactory();
var cProduct = c.buildProduct(); //create a ChildProduct with x=a, y=b

buildProduct determine whether it has been requested to create a new
product of its own, or some derived-factory requesting it to build its
own part only

You should provide some safeguard mechanism of your own, like checking
whether the product is a derived class from ChildProduct in
ChildFactory.buildProduct. That'll avoid user from passing something like:
childFactory.buildProduct(new BaseProduct()); //yak

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