Should warn for ?. in expression of foreach

[ArtBlnd]

Theres no WAY to handle ?. operator with foreach.
It should emit compile warning or error.
it just thorws NullReferencedException when nullptr object in it(from GetEnumerator)

class Program
{
        class Foo
        {
            public Bar bar = null;
        }
        class Bar
        {
            public List<int> list = new List<int>(2);
        }
        static void Main(string[] args)
        {
            Foo foo = new Foo();
            //It creates ?. check assembly but doesn't handle. also try to send 
            // DWORD PTR[foo.bar] to GetEnumerator so it throws NullReferencedException(nullptr)
            foreach (int j in foo.bar?.list)
            {
                System.Console.WriteLine(j);
            }
        }
}

[ArtBlnd]

OR just tacitly handle foreach .? operator from CoreCLR(just passing object if nullptr(loop continue))

[jmarolf]

Are you saying that:

static void Main(string[] args)
{
    Foo foo = new Foo();
    foreach (int j in foo.bar?.list)
    {
        System.Console.WriteLine(j);
    }
}

Should translate to:

static void Main(string[] args)
{
    Foo foo = new Foo();
    foreach (int j in foo.bar != null 
        ? foo.bar.list
        : Enumerable.Empty<int>().ToList())
    {
        System.Console.WriteLine(j);
    }
}

?. returns null for the expression instead of throwing a null reference exception. what do you expect the following to do?

static void Main(string[] args)
{
    Foo foo = new Foo();
    foreach (int j in null as List<int>)
    {
        System.Console.WriteLine(j);
    }
}

foreach attempts to get the enumerator from the list. If the expression is null, this will always throw a null reference exception.

A simple fix for this is the ?? operator

static void Main(string[] args)
{
    Foo foo = new Foo();
    foreach (int j in foo.bar?.list ?? Enumerable.Empty<int>())
    {
        System.Console.WriteLine(j);
    }
}

[svick]

I think a warning would be appropriate here. By using ?., you say that you want to get null, but foreach won't be able to handle that. Though this would probably have to be a part of a warning wave (#1580).

[ArtBlnd]

@svick That is actually what I mean

[HaloFour]

This would probably automatically get picked up by #5032 as a possible dereference of a nullable reference type.

[ygoe]

What if foreach actually could handle null? See #6563