CODEWITHSUNDEEP
c#.netgenericstype-inference
Alois
Alois

Reputation: 431

Inference of second generic argument

I have the class structure like below:


public interface IBinder<T>
    where T : Control
{
    T Control { get; }
}

public class ButtonBinder : IBinder<Button>
{
    public ButtonBinder(Button control)
    {
        Control = control ?? throw new ArgumentNullException(nameof(control));
    }

    public Button Control { get; private set; }
}

Create instances of that Binder I want with help of a factory method like this:

public void Main()
{
    // This line works.
    var binder = RegisterBinder<ButtonBinder, Button>(new Button());

    // But I want use type inference like this:
    var binder2 = RegisterBinder<ButtonBinder>(new Button());
}

/// <summary>
/// My pseudo-factory.
/// </summary>
public T_Binder RegisterBinder<T_Binder, T_Control>(T_Control control)
    where T_Binder : IBinder<T_Control>
    where T_Control : Control
{
    return (T_Binder)Activator.CreateInstance(typeof(T_Binder), control);
}

Because the class 'ButtonBinder' declares the generic control type 'Button' the Compiler should be able to infer it. How I can tell the compiler that I want to use type inference?

Thank you.

Upvotes: 0

Views: 70

Answers (1)

Jason
Jason

Reputation: 1555

Unfortunately C# cannot infer only one of multiple generic parameters. However, if you do not mind capturing the inferable type in an intermediate class you can do something like this:

public class Factory
{
    public void Main()
    {
        // This line works.
        var binder = RegisterBinder<ButtonBinder, Button>(new Button());

        // Now only T_Binder is needed
        var binder2 = ForControl(new Button()).RegisterBinder<ButtonBinder>();
    }

    private BinderRegistration<T_Control> ForControl<T_Control>(T_Control control) where T_Control : Control
    {
        return new BinderRegistration<T_Control>(control);
    }

    /// <summary>
    /// My pseudo-factory.
    /// </summary>
    public T_Binder RegisterBinder<T_Binder, T_Control>(T_Control control)
        where T_Binder : IBinder<T_Control>
        where T_Control : Control
    {
        return (T_Binder)Activator.CreateInstance(typeof(T_Binder), control);
    }
}

internal class BinderRegistration<T_Control>
    where T_Control : Control
{
    private readonly Control _control;

    public BinderRegistration(Control control)
    {
        _control = control;
    }

    public T_Binder RegisterBinder<T_Binder>() 
        where T_Binder : IBinder<T_Control>
    {
        return (T_Binder)Activator.CreateInstance(typeof(T_Binder), _control);
    }
}

Upvotes: 1

Related Questions