What is the easiest and most compact way to create a IEnumerable<T> or ICollection<T>?

Question

So, many times we have a function that accepts an IEnumerable or ICollection as a parameter. In cases where we have single items, but no collection to hold them, we must create a collection before passing them to the function, like:

T o1, o2, o3;
Foo(new T[] { o1, o2, o3 });

I've always created an array or a list, like I've done in the last example. But I wonder, is there a more elegant way to create the required IEnumerable or ICollection?

It would be quite cool, if one could do this:

Foo({ o1, o2, o3 });

And the compiler would create the most abstract possible collection that would satisfy the needs of IEnumerable or ICollection (depending on which one the function accepts).

Anyhow, how you would pass o1, o2 and o3 to an IEnumerable or ICollection parameters?

Answer 1

The current version of C# (3) supports a notation without explicit type, i.e.

Foo(new [] { o1, o2, o3 })

to create an array. There’s also Linq’s Enumerable.Range to create a continuous range of numbers. Everything else has to be implemented. In the spirit of Java:

public static IEnumerable<T> AsList<T>(params T[] values) {
    return values;
}

to be called like this:

Foo(Enumerable.AsList(o1, o2, o3));