.NET 4.0 Generic Invariant, Covariant, Contravariant
- by Sameer Shariff
Here's the scenario i am faced with:
public abstract class Record { }
public abstract class TableRecord : Record { }
public abstract class LookupTableRecord : TableRecord { }
public sealed class UserRecord : LookupTableRecord { }
public interface IDataAccessLayer<TRecord>
where TRecord : Record { }
public interface ITableDataAccessLayer<TTableRecord> : IDataAccessLayer<TTableRecord>
where TTableRecord : TableRecord { }
public interface ILookupTableDataAccessLayer<TLookupTableRecord> : ITableDataAccessLayer<TLookupTableRecord>
where TLookupTableRecord : LookupTableRecord { }
public abstract class DataAccessLayer<TRecord> : IDataAccessLayer<TRecord>
where TRecord : Record, new() { }
public abstract class TableDataAccessLayer<TTableRecord> : DataAccessLayer<TTableRecord>, ITableDataAccessLayer<TTableRecord>
where TTableRecord : TableRecord, new() { }
public abstract class LookupTableDataAccessLayer<TLookupTableRecord> : TableDataAccessLayer<TLookupTableRecord>, ILookupTableDataAccessLayer<TLookupTableRecord>
where TLookupTableRecord : LookupTableRecord, new() { }
public sealed class UserDataAccessLayer : LookupTableDataAccessLayer<UserRecord> { }
Now when i try to cast UserDataAccessLayer to it's generic base type ITableDataAccessLayer<TableRecord>, the compiler complains that it cannot implicitly convert the type.
