Where T: IEnumerable <T> method restriction

Question

From time to time I try to torture the C # compiler. Today I came up with this:

static void CallFirst<T>(T a) where T : IEnumerable<T>
{
    a.First().ToString();
}

It was a simple mistake, because I wanted to create a general method that takes as a parameter a parameter, which, of course, should look like this:

static void CallFirst2<T>(IEnumerable<T> a)
{
    a.First().ToString();
}

Anyway, is it even possible to call a method CallFirst()? Each time a collection is transferred, collection collection is expected.

If this is not the case, should this not be taken as a compile-time error?

Answer 1

Of course:

class Test : IEnumerable<Test>
{
    IEnumerator<Test> IEnumerable<Test>.GetEnumerator()
    {
        throw new NotImplementedException();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }
}

    ...

var test = new Test();
CallFirst(test);

Answer 2

IEnumerable<T> , ( - IComparable<T>), .