Question

I am trying to return IEnumerable<IMyInterface>. I have a class, MyClass:IMyInterface that I return from a function.

IEnumerable<IMyInterface> test() {
    tmpList = new List<MyClass>();
    tmp1 = new MyClass();
    tmp2 = new MyClass();
    tmpList.Add(tmp1);
    tmpList.Add(tmp2);
    return tmpList;
}

Compiler will not permit, which seems odd to me since MyClass:MyInterface. Compiler gives error along the lines of 'cannot implicitly convert type System.Collections.Generic.IEnumerable<MyClass> to System.Collections.Generic.IEnumerable<IMyInterface. An explicit conversion exists. Are you missing a cast?'

I can’t perform return (IEnumerable<IMyInterface>)tmp without cast exception at runtime. What am I missing? I would expect returning IEnumerable of interface should work fine.

Answer 1

You should do this:

IEnumerable<IMyInterface> test() {
    tmpList = new List<IMyInterface>();  // this is the important bit
    tmp1 = new MyClass();
    tmp2 = new MyClass();
    tmpList.Add(tmp1);
    tmpList.Add(tmp2);
    return tmpList;
}

Alternatively, you could do this:

return tmpList.Cast<IMyInterface>(); // requires using System.Linq in usings