Cannot instantiate a generic class

Question

I have an Interface

public interface ICrypto<T> : IDisposable
{
     ICryptoTransform GetDecryptor();

     ICryptoTransform GetEncryptor();

     T GetAlgorithm();
}

I have an implementation

public class TripleDESCryptoProvider : ICrypto<TripleDESCryptoServiceProvider>
{

    public TripleDESCryptoProvider() { }

    public ICryptoTransform GetDecryptor()
    {
        return GetAlgorithm().CreateDecryptor();
    }

    public ICryptoTransform GetEncryptor()
    {
        return GetAlgorithm().CreateEncryptor();
    }

    public TripleDESCryptoServiceProvider GetAlgorithm()
    {
     ...
    }

    public void Dispose()
    {
        throw new NotImplementedException();
    }
}

i have a class that implements implementation above

public class CryptoWork<T> where T : ICrypto<T>, new()
{
    protected static T _keyStore;

    public static T KeyStore
    {
        get
        {
            if (_keyStore == null)
            {
                _keyStore = new T();
            }
            return _keyStore;
        }
    }

    /// <summary>
    /// Encrypt a byte array
    /// </summary>
    public string Encrypt(string input)
    {
        byte[] inputArray = UTF8Encoding.UTF8.GetBytes(input);
        using (var encryptor = KeyStore.GetEncryptor())
        {
            return Convert.ToBase64String(encryptor.TransformFinalBlock(inputArray, 0, inputArray.Length));
        }
    }

    /// <summary>
    /// Decrypt a byte array
    /// </summary>
    public string Decrypt(string input)
    {
        byte[] inputArray = Convert.FromBase64String(input);
        using (var encryptor = KeyStore.GetDecryptor())
        {
            return UTF8Encoding.UTF8.GetString(encryptor.TransformFinalBlock(inputArray, 0, inputArray.Length));
        }
    }
}

I am having problem instantiating class CryptoWork<T> where T : ICrypto<T>, new() :

Neither

 var cryptoWork = new CryptoWork < ICrypto < TripleDESCryptoProvider > > ();

nor

var cryptoWork = new CryptoWork < TripleDESCryptoProvider > ();

compiles.

Answer 1

You have specified:

CryptoWork<T> where T : ICrypto<T>, new()

and you are using

new CryptoWork<TripleDESCryptoProvider>();

For that to work, we would need:

TripleDESCryptoProvider : ICrypto<TripleDESCryptoProvider>

(since T = TripleDESCryptoProvider )

But you have:

TripleDESCryptoProvider : ICrypto<TripleDESCryptoServiceProvider>

and a public parameterless constructor (which you have). Options:

• make TripleDESCryptoProvider : ICrypto<TripleDESCryptoProvider>
• refactor the API
• make the CryptoWork type have 2 generic type parameters; one for the TripleDESCryptoProvider , another for the TripleDESCryptoServiceProvider