Warcaith Posts - Answer Overflow

Warcaith

•Created by Warcaith on 4/15/2024 in #help

Issue with generic interfaces (covariance/contravariance)

Hello! Currently, I have these interfaces within my project:

c#
public interface IResult<out TResponse>
{
    public bool Success { get; }
    public TResponse? Response { get; }
}

public interface ICommand<in TOptions, out TResponse>
{
    IResult<TResponse?> Execute(TOptions options);
}

public interface ICommand<in TOptions>
{
    IResult<object?> Execute(TOptions options);
}

public interface ICommand
{
    IResult<object?> Execute(object options);
}

public class CommandOptions
{

}

public class Command : ICommand<CommandOptions>
{
    public IResult<object?> Execute(CommandOptions options) 
    {
    }
}

c#
public interface IResult<out TResponse>
{
    public bool Success { get; }
    public TResponse? Response { get; }
}

public interface ICommand<in TOptions, out TResponse>
{
    IResult<TResponse?> Execute(TOptions options);
}

public interface ICommand<in TOptions>
{
    IResult<object?> Execute(TOptions options);
}

public interface ICommand
{
    IResult<object?> Execute(object options);
}

public class CommandOptions
{

}

public class Command : ICommand<CommandOptions>
{
    public IResult<object?> Execute(CommandOptions options) 
    {
    }
}

However, I'm unable to create a command like this:

c#
object options = new CommandOptions();
ICommand<object> command = new Command();
command.Execute(options);

c#
object options = new CommandOptions();
ICommand<object> command = new Command();
command.Execute(options);

Cannot implicitly convert type 'Command' to 'ICommand<object>'. An explicit conversion exists (are you missing a cast?)

Cannot implicitly convert type 'Command' to 'ICommand<object>'. An explicit conversion exists (are you missing a cast?)

... which makes it impossible for me to create a command and options dynamically. I have probably a design issue within my interfaces, so please, if there's anything that should be changed, don't hesitate to make these changes. Thanks! 😁 (Downcasting to ICommand<object> gives me an System.InvalidCastException)

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