CODEWITHSUNDEEP
c#
Robpaulsen
Robpaulsen

Reputation: 3

C# compile-time type-conversion error

I'm getting a compile-time type conversion error with this code... dunno if i'm just tired, but I can't figure out what I need to change in the class to fix this. Any pointers would be awesome, thanks

The error is: "error CS0266: Cannot implicitly convert type csharpfinal.Packaging<string> to csharpfinal.IGetValue<object>. An explicit conversion exists (are you missing a cast?)"

    interface ISetValue<T>
    {
         void SetData(T data);
    }

    interface IGetValue<T>
    {
         T GetData();
    }

    class Packaging<T> : ISetValue<T>, IGetValue<T>
    {
     private T storedData;
     void ISetValue<T>.SetData(T data)
     {
         this.storedData = data;
     }
     T IGetValue<T>.GetData()
     {
     return this.storedData;
     }
    }

    class Program
    {        
     static void Main(string[] args)
     {
            Packaging<string> stringPackage = new Packaging<string>();
            ISetValue<string> setStringValue = stringPackage;
            setStringValue.SetData("Sample string");
            // the line below causes a compile-time error
            IGetValue<object> getObjectValue = stringPackage;

     Console.WriteLine("{0}", getObjectValue.GetData());
     }
    }

Upvotes: 0

Views: 176

Answers (4)

Dan
Dan

Reputation: 1001

Packaging<string> stringPackage = new Packaging<string>();

^ generic type is string

IGetValue<object> getObjectValue = stringPackage;

but you are trying to cast an object generic to a string generic, that's why you get the compile-time error.

You can change the generic type of your object initialization to object to fix it:

Packaging<object> stringPackage = new Packaging<object>();
ISetValue<object> setStringValue = stringPackage;

Upvotes: 0

Joonas Koski
Joonas Koski

Reputation: 269

IGetValue<object>

Should this be 

IGetValue<string>

Upvotes: 0

DevEstacion
DevEstacion

Reputation: 1967

Modify this code

interface ISetValue<T>
{
     void SetData(T data);
}

interface IGetValue<T>
{
     T GetData();
}

to

interface ISetValue<in T>
{
    void SetData(T data);
}

interface IGetValue<out T>
{
    T GetData();
}

For generic type parameters, the out keyword specifies that the type parameter is covariant. You can use the out keyword in generic interfaces and delegates.

Covariance enables you to use a more derived type than that specified by the generic parameter. This allows for implicit conversion of classes that implement variant interfaces and implicit conversion of delegate types. Covariance and contravariance are supported for reference types, but they are not supported for value types.

Upvotes: 2

dotnetstep
dotnetstep

Reputation: 17485

interface ISetValue<in T>
    {
        void SetData(T data);
    }

    interface IGetValue<out T>
    {
        T GetData();
    }

    class Packaging<T> : ISetValue<T>, IGetValue<T>
    {
        private T storedData;
        void ISetValue<T>.SetData(T data)
        {
            this.storedData = data;
        }
        T IGetValue<T>.GetData()
        {
            return this.storedData;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Packaging<string> stringPackage = new Packaging<string>();
            ISetValue<string> setStringValue = stringPackage;
            setStringValue.SetData("Sample string");
            // the line below causes a compile-time error
            IGetValue<object> getObjectValue = stringPackage;

            Console.WriteLine("{0}", getObjectValue.GetData());
        }
    }

more info :http://msdn.microsoft.com/en-us/library/dd469487.aspx

Upvotes: 0

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