Question

i have an object that is a:

IQueryable<Foo>

and i want to pass it into a function that expects a:

IQueryable<IFoo>

Foo DOES implements IFoo

why wouldn’t this compile? what is the best way to convert to have this work?

Answer 1

Co- and contra- variance were added in the .NET 4 BCL, and do not exist in the .NET 3.5 BCL.

You can work around this limitation in 3.5 by using the Select operation to cast to your interface type:

IQueryable<Foo> foos = ..;
myFunc(foos.Select(x => (IFoo)x));

Edit (from Reed’s comment, below):

IQueryable<Foo> foos = ..;
myFunc(foos.Cast<IFoo>());