c# - The type cannot be used as type parameter 'T' in the generic type or method 'BaseController<T>'. There is no implicit reference -

i'm trying create generic simplify codes (it's web api project), @ somehow it's ended becoming more complicated expected. i'm trying implement this:

to simplify whole real code, i've written:

public interface idatabasetable { }  public class receiptindex: idatabasetable { }  public interface ibackend<t> t: idatabasetable { }  public class receipts : ibackend<receiptindex> { }  public class generic<t> : synctwowayxi, ibackend<t> t:idatabasetable { }  public class basecontroller<t> : apicontroller t: ibackend<idatabasetable>, new () { } 

all of line above created separately in own file.

when try create controller inherit basecontroller

public class receiptsbasecontroller : basecontroller<receipts> 

i error said

the type 'receipts' cannot used type parameter 't' in generic type or method 'basecontroller'. there no implicit reference conversion 'receipts' 'ibackend'.

i try find similar problem , end called covariance , contravariance problem. can give feedback i'm trying or maybe can simplify it.

you can try specify t in ibackend. this:

public class basecontroller<t, tbackendsubtype> : apicontroller     t : ibackend<tbackendsubtype>, new()     tbackendsubtype : idatabasetable { }  public class receiptsbasecontroller : basecontroller<receipts, receiptindex> { }