Cannot implicitly convert MyType to MyType

Question

I am not sure if this is a Covariance and Contravariance issue but I cannot get this working. Here is the code:

public interface IDto { }

public class Pagin         


        

Answer 1

Yes this is a variance issue. You need to create an interface (only interfaces and delegates can be co/contravariant) IPaginatedDto<out TDto> where the Dtos cannot have a setter (otherwise you cannot use out):

public interface IPaginatedDto<out TDto> where TDto : IDto
{
    int PageIndex { get; set; }
    int PageSize { get; set; }
    int TotalCount { get; set; }
    int TotalPageCount { get; set; }
    bool HasNextPage { get; set; }
    bool HasPreviousPage { get; set; }
    IEnumerable<TDto> Dtos { get; }
}

And your PaginatedDto<TDto> will implement this interface:

public class PaginatedDto<TDto> : IPaginatedDto<TDto> where TDto : IDto
{

    public int PageIndex { get; set; }
    public int PageSize { get; set; }
    public int TotalCount { get; set; }
    public int TotalPageCount { get; set; }

    public bool HasNextPage { get; set; }
    public bool HasPreviousPage { get; set; }

    public IEnumerable<TDto> Dtos { get; set; }
}

And use the interface in your method:

private static void ProcessDto(IPaginatedDto<IDto> paginatedDto)
{

    //Do work...
}