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c#polymorphismextension-methodsstatic-polymorphism
Salman Hasrat Khan
Salman Hasrat Khan

Reputation: 2006

c# Dispatching Extension Methods based on Value not Reference

Given the following 2 extension methods

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

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

and the following 2 invocations

//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

How can I execute the second extension method even though its reference type is object but its value type is a EntityRestIdentityDescriber? I'm looking for static polymorphism.

Upvotes: 1

Views: 434

Answers (2)

cyan
cyan

Reputation: 309

You need double dispatch.Double dispatch determine dispatch based on the actual type at runtime

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
//......

Upvotes: 0

Ali Sheikh Nezami
Ali Sheikh Nezami

Reputation: 172

try this

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

Upvotes: 1

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