Can I restrict generic method to more than one interface?

Question

I have a generic method

public static void DoSomething<T>()
{...}

. Now I want to restrict that T.

public static void DoSomething<T>() where T: IInterface1
{...}

But what I really want is allowing multiple interfaces, something like

public static void DoSomething<T>() where T: IInterface1, IInterface2
{...}

But that doesn't work. Compiler says something like

There's no implicit conversion from IInterface1 to IInterface2

There's no implicit conversion from IInterface2 to IInterface1

I thought about letting the classes implement a common interface which I can refer to but I don't have access to the classes.

What possibilities do I have to allow multiple Interfaces?

Thanks, Tobi

Edit: Here's what I wanted to do. I'm developing an Outlook-Add-In. I use this piece of code below quite often.

    public static object GetItemMAPIProperty<T>(AddinExpress.MAPI.ADXMAPIStoreAccessor adxmapiStoreAccessor, object outlookItem, uint property) where T: Outlook.MailItem, Outlook.JournalItem
    {
        AddinExpress.MAPI.MapiItem mapiItem;
        mapiItem = adxmapiStoreAccessor.GetMapiItem(((T)outlookItem));
        return mapiItem != null ? mapiItem.GetProperty(property) : null;
    }

The method GetMapiItem takes an object as long as it's one of Outlook's items (Journal, Mail, Contact,...). That's why I was restricting T. Because it cannot be, say, Outlook.MAPIFolder.

No I've changed the method to

    public static object GetItemMAPIProperty<T>(AddinExpress.MAPI.ADXMAPIStoreAccessor adxmapiStoreAccessor, T outlookItem, uint property)
    {
        AddinExpress.MAPI.MapiItem mapiItem;
        mapiItem = adxmapiStoreAccessor.GetMapiItem(((T)outlookItem));
        return mapiItem.GetProperty(property);
    }

but the developer (In this case I) can give it any Type because the method GetMapiItem accepts an object. I hope that makes sense. I'm not sure if it does for that example but I guess restricting a generic method to multiple Types (with OR) can be a good idea.

Answer 1

This compiles fine for me:

interface I1 { int NumberOne { get; set; } }
interface I2 { int NumberTwo { get; set; } }

static void DoSomething<T>(T item) where T:I1,I2
{
    Console.WriteLine(item.NumberOne);
    Console.WriteLine(item.NumberTwo);
}

So the syntax seems fine... perhaps its something else that's causing the problem.