Null propagating expression of struct type requires to be wrapped in parenthesis

[MrTA2]

Consider the following:

class A { public int X; }
A? a = GetA();
int? x = a?.X; // fine
string? s = a?.X?.ToString(); // broken
string? s2 = (a?.X)?.ToString(); // fine

Why is it so? The a?.X?.ToString() looks like valid syntax, but the compiler doesn't like it.

To make things worse, VS suggests removing parentheses from (a?.X)?.ToString() which is impossible, as it leads to a compilation error.

[HaloFour]

You want:

string? s = a?.X.ToString();

This behavior is by design. The null-propagating operator bails immediately on the first null, you don't have to chain the operator to the right in the expression. It's not possible for the intermediate value in a?.X to be null unless it's wrapped in paranthesis.

[HaloFour]

You might need to chain if X was itself nullable, e.g.:

class A { public int? X }
string? s = a?.X?.ToString();

That basically expands into:

string? s;
if (a != null)
{
    int? temp = a.X;
    if (temp != null)
    {
        s = temp.Value.ToString();
    }
    else
    {
        s = null;
    }
}
else
{
    s = null;
}