Question

假设以下课程

// What I have created ...

public abstract class TaxServiceProvider<T, S>
    where T : TaxServiceProviderConfig
    where S : TaxServiceInfo
{
    protected T Config { get; set; }

    public abstract S GetTax(int zipCode);
}

public abstract class TaxServiceInfo { ... }
public abstract class TaxServiceProviderConfig { ... }

// What I want to create ...

public class SpecialTaxServiceProvider<T, S> : TaxServiceProvider<SpecialTaxServiceProviderConfig, SpecialTaxServiceInfo>
    where T : SpecialTaxServiceProviderConfig
    where S : SpecialTaxServiceInfo
{ ... }
public class SpecialTaxServiceInfo : TaxServiceInfo { ... }
public class SpecialTaxServiceProviderConfig : TaxServiceProviderConfig { ... }

其中TaxServiceInfo和TaxServiceProviderConfig用于支持TaxServiceProvider类。

我想从SpecialTaxServiceProvder创建一个派生类TaxServiceProvider（非抽象），它的通用方式与TaxServiceProvider相同，并且SpecialTaxServiceInfo和{ {1}}作为类型。

我想在SpecialTaxServiceProviderConfig中实施GetTax和Config，以便SpecialTaxServiceProvider返回GetTax类型，SpecialTaxServiceInfo类型为{{1} }}

然后，我会创建一个派生自Config的附加类，以及派生自SpecialTaxServiceProviderConfig和SpecialTaxServiceProvider

的类

SpecialTaxServiceInfo

此类的SpecialTaxServiceProviderConfig返回类型public class A_SpecialTaxServiceProvider : SpecialTaxServiceProvider<A_SpecialTaxServiceProviderConfig, A_SpecialTaxServiceInfo> { ... } public class A_SpecialTaxServiceProviderConfig : SpecialTaxServiceProviderConfig { ... } public class A_SpecialTaxServiceInfo : SpecialTaxServiceInfo { ... }，此类的GetTax类型为A_SpecialTaxServiceInfo

我已经研究过C＃中的协方差和泛型类的语法，但是我不确定我尝试做的是不可能的语言，或者我只是不知道设置它的正确方法起来。

Answer 1

更改SpecialTaxServiceProvider并将T和S传递给TaxServiceProvider：

public class SpecialTaxServiceProvider<T, S> : TaxServiceProvider<T, S>
    where T : SpecialTaxServiceProviderConfig
    where S : SpecialTaxServiceInfo
{
    public override S GetTax(int zipCode)
    {
        return null;
    }
}

实施A_SpecialTaxServiceProvider并覆盖GetTax：

public class A_SpecialTaxServiceProvider : SpecialTaxServiceProvider<A_SpecialTaxServiceProviderConfig, A_SpecialTaxServiceInfo>
{
    public override A_SpecialTaxServiceInfo GetTax(int zipCode)
    {
        return null;
    }
}

它会阻止您创建

public class A_SpecialTaxServiceProvider : SpecialTaxServiceProvider<A_SpecialTaxServiceProviderConfig, TaxServiceInfo>

有以下错误：

“Project.TaxServiceInfo”类型不能用作类型泛型类型或方法中的参数'S' 'Project.SpecialTaxServiceProvider'。没有隐含的引用从'Project.TaxServiceInfo'转换为 'Project.SpecialTaxServiceInfo'。

Answer 2

我决定在构造函数中使用函数委托，允许我传入工厂方法来创建我的泛型类型。

这是我最终的结果

// Tier 1 of my class hierarchy
public abstract class TaxServiceProvider<C, I>
    where C : TaxServiceProviderConfig
    where I : TaxServiceInfo
{
    protected C Config { get; set; }

    public abstract I GetTax(int zipCode);
}

public abstract class TaxServiceInfo {
    public TaxServiceInfo(string param1, string param2, int param3, ect...) {
        ...
    }
}

public abstract class TaxServiceProviderConfig { ... }


// Tier 2 of my class hierarchy
public class DerivedTaxServiceProvider<C, I> : TaxServiceProvider<C, I>
    where C : DerivedTaxServiceProviderConfig
    where I : DerivedTaxServiceInfo
{
    protected Func<S, string, string, int, ect...> Factory;

    public DerivedTaxServiceProvider (C config, Func<I, string, string, int, ect...> factory) {
        Config = config;
        Factory = factory;
    }

    public override I GetTax(int zipCode) {
        ...
        I taxServiceInfo = Factory("param1", "param2", 3, ect...);
        ...
        return I;
    }
}

public class DerivedTaxServiceInfo : TaxServiceInfo {
    public DerivedTaxServiceInfo(string param1, string param2, int param3, ect...) 
        : base(param1, param2, param3, ect...) 
    { ... }
}

public class DerivedTaxServiceProviderConfig : TaxServiceProviderConfig { ... }

// Tier 3 of my class hierarchy
public class ConcreteTaxServiceProvider : DerivedTaxServiceProvider<ConcreteTaxServiceProviderConfig, ConcreteTaxServiceInfo> {
    public ConcreteTaxServiceProvider(ConcreteTaxServiceProviderConfig config, Func<ConcreteTaxServiceInfo, string, string, int, ect...> factory) {
        Config = config;
        Factory = factory;
    }

    public override ConcreteTaxServiceInfo GetTax(int zipCode) {
        return base.GetTax(zipCode);
    }
}

public class ConcreteTaxServiceInfo : DerivedTaxServiceInfo {
    public ConcreteTaxServiceInfo(string param1, string param2, int param3, ect...) 
        : base(param1, param2, param3, ect...) 
    { ... }

    public static ConcreteTaxServiceInfo CreateConcreteTaxServiceInfo(string param1, string param2, int param3, ect...) {
        return new ConcreteTaxServiceInfo(param1, param2, param3, etc...);
    }
}

public class ConcreteTaxServiceProviderConfig : DerivedTaxServiceProviderConfig { ... }

// Implementation of my class hierarchies
public void method() {
    ConcreteTaxServiceProviderConfig() config = new ConcreteTaxServiceProviderConfig();

    ConcreteTaxServiceProvider provider = new ConcreteTaxServiceProvider(config, ConcreteTaxServiceInfo.CreateConcreteTaxServiceInfo);

    ConcreteTaxServiceInfo serviceInfo = provider.GetTax(99939);
}

所以基本上我有2级泛型类。第二级Provider类重写了“GetTax”的基本抽象方法，但我不希望它返回一个具体类型，因为那时我无法在从它继承的类中干净地调用该方法。在具体（第3级）提供程序中调用“GetTax”时，我不得不将派生的ServiceInfo转换为ConcreteServiceInfo类型。

只要我在Info类中有一个与我的委托匹配的构造函数，无论Info类的子类化级别（在第二级以下），我都可以将它提供给我的提供者并使用第二级的Provider class GetTax方法。

这个工厂方法在Provider构造函数的参数列表中看起来很丑陋，而创建Info类的静态方法似乎很尴尬，但它确实有用！

这是我提出的提出这个解决方案的问题：C# generics problem - newing up the generic type with parameters in the constructor

从泛型基类派生的泛型类

2 个答案: