c# - 我如何改进此代码 : Inheritance and IEquatable<>

Question

这是一个关于我正在尝试做的事情的例子:

public class Foo : IEquatable<Foo>
{
    public bool Equals(Foo other)
    {
        Type type1 = this.GetType();
        Type type2 = other.GetType();

        if (type1 != type2)
            return false;

        if (type1 == typeof(A))
        {
            A a = (A)this;
            A b = (A)other;

            return a.Equals(b);
        }
        else if (type1 == typeof(B))
        {
            B c = (B)this;
            B d = (B)other;

            return c.Equals(d);
        }
        else
        {
            throw new Exception("Something is wrong");
        }
    }
}

public class A : Foo, IEquatable<A>
{
    public int Number1 { get; set; }
    public int Number2 { get; set; }

    public bool Equals(A other)
    {
        return this.Number1 == other.Number1 && this.Number2 == other.Number2;
    }
}

public class B : Foo, IEquatable<B>
{
    public int Number1 { get; set; }
    public int Number2 { get; set; }
    public int Number3 { get; set; }

    public bool Equals(B other)
    {
        return this.Number1 == other.Number1 && this.Number2 == other.Number2 && this.Number3 == other.Number3;
    }
}

但是正如您在上面看到的，我必须使用许多条件句“if”来识别真实类型。问题是我必须使用基类。例如:

A a = new A();
Foo foo = a;

foo.Equals(another);

Answer 1

作为对您问题的直接回答，您似乎实现了 IEquatable<Foo>通过始终遵循(具体的)子类的 IEquatable<self>执行。这看起来像:

(错误代码，仅供演示)

// You need to specify what you want when this method is called on a 
// vanilla Foo object. I assume here that Foo is abstract. If not, please
// specify desired behaviour.
public bool Equals(Foo other)
{
    if (other == null || other.GetType() != GetType())
        return false;

    // You can cache this MethodInfo..
    var equalsMethod = typeof(IEquatable<>).MakeGenericType(GetType())
                                           .GetMethod("Equals");

    return (bool)equalsMethod.Invoke(this, new object[] { other });
}

但真的并不清楚为什么你需要相等比较总是“通过”基类的 IEquatable<self>实现。

框架已经有了虚拟Equals将导致将相等调用分派(dispatch)到适当方法的方法。此外，EqualityComparar<T>.Default (大多数集合类型使用它来进行相等性检查)已经有选择的智慧 IEquatable<self>.Equals(self)或 object.Equals(object)视情况而定。

据我所知，尝试在仅转发请求的基类中创建相等性的实现是没有任何值(value)。

没有进一步解释为什么您需要基类 IEquatable<>实现，我建议只对每种类型正确实现平等。例如:

public class A : Foo, IEquatable<A>
{
    public int Number1 { get; set; }
    public int Number2 { get; set; }

    public bool Equals(A other)
    {
        return other != null 
            && Number1 == other.Number1
            && Number2 == other.Number2;
    }

    public override bool Equals(object obj)
    {
        return Equals(obj as A);
    }

    public override int GetHashCode()
    {
        return Number1 ^ Number2;
    }
}