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Accepted
beyarkay
Asked: 2024-06-27 20:35:27 +0800 CST

C# 中的类型状态模式

  • 772

我想在 C# 中实现typestate 模式。我尝试过类似以下方法：

interface Open {}
interface Closed {}

abstract class Foo<T> { }

class Bar<T> where T: Closed { }
class Bar<T> where T: Open { }

以及其他排列，但它们最终都会导致编译器抱怨。这个特定示例给出（来自https://www.programiz.com/csharp-programming/online-compiler/）：

/tmp/qmk1tTLHWG.cs(12,11): error CS0101: The namespace 'baz' already contains a definition for 'Bar'
/tmp/qmk1tTLHWG.cs(11,11): error CS0265: Partial declarations of 'Bar<T>' have inconsistent constraints for type parameter 'T'

我对 C# 的类型系统了解不够，不知道什么会真正起作用，而且我找不到太多关于如何做到这一点的文档。是否有可能实现类型状态模式？我找到了Adam 的博客，但他实际上并没有实现图1所示的类型状态模式，如果可能的话，这正是我想要做的。

理想情况下，我想要类似的东西

struct Closed { }; 
struct Open { };

class Foo<T> {
    // functions applicable to Foo's in both the Closed and Open states
}

class Foo<Closed> {
    // functions applicable to Foo's in just the Open state
}

class Foo<Open> {
    // functions applicable to Foo's in just the Open state
}
c#

1 个回答

  1. Best Answer

    您应该通过接口对此进行建模，但只需要一个类。

    一个例子：

    interface IOpen
{
    IClosed Close();
}

interface IClosed
{
    IOpen Open();
}

class Foo : IOpen, IClosed
{
    public IOpen Open()
    {
        return this;
    }

    public IClosed Close()
    {
        return this;
    }
}

var foo = new Foo();
var open = foo.Open();

var closed = open.Close(); // Only Close() is allowed on an open foo
closed.Open(); // Only Open() is allowed on an closed foo

    Foo您可以通过使用工厂方法强制默认状态来扩展此功能：

    class Foo : IOpen, IClosed
{
    private Foo() // Prevent manual instantiation (using new)
    { }

    public static IClosed Create() // Return closed by default
    {
        return new Foo();
    }

    public IOpen Open()
    {
        return this;
    }

    public IClosed Close()
    {
        return this;
    }
}

var closed = Foo.Create();
var open = closed.Open(); // Only Open() is allowed by default
    • 5

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