c# 基於值而不是引用調度擴展方法

Question

鑒於以下2種擴展方法

public static string getIDPropertyName(this object value)
{
    return "ID";
}

public static string getIDPropertyName<IDType>(this EntityRestIdentityDescriber<IDType> entityIdentityDescriber)
{
    return entityIdentityDescriber.propertyNameDescribingID();
}

以及以下 2 次調用

//arrange

object test = new CustomEntityRestModelIdentity();
//test.UserName = "KKK";
//act
var actual = test.getIDPropertyName(); //calls the first extension method
var actual2 = (test as CustomEntityRestModelIdentity).getIDPropertyName(); //calls the second extension method

即使它的引用類型是對象但它的值類型是 EntityRestIdentityDescriber，我如何執行第二個擴展方法？ 我正在尋找靜態多態性。

Answer 1

嘗試這個

public static string getIDPropertyName(this object entityIdentityDescriber)
{
    if(entityIdentityDescriber is EntityRestIdentityDescriber<IDType>)
        return entityIdentityDescriber.propertyNameDescribingID();
    else
        return "id";
}

Answer 2

你需要double dispatch 。 Double dispatch根據運行時的實際類型確定調度

public class IdPropertyNameResolver
{
    public string GetIDPropertyName(object value)=>"ID";

    public string GetIDPropertyName<T>(EntityRestIdentityDescriber<T> value)=>
        value.propertyNameDescribingID();
}
//......do something
object o = new CustomEntityRestModelIdentity();
new IdPropertyNameResolver().GetIDPropertyName((dynamic)o);//CustomEntityRestModelIdentity id name
//......