Variable type ending with ?

Question

What does ? mean:

public bool? Verbose { get; set; }

When applied to string?, there is an error:

Answer 1

The ? is shorthand for the struct below:

struct Nullable<T>
{
    public bool HasValue;
    public T Value;
}

You can use this struct directly, but the ? is the shortcut syntax to make the resulting code much cleaner. Rather than typing:

Nullable<int> x = new Nullable<int>(125);

Instead, you can write:

int? x = 125;

This doesn't work with string, as a string is a Reference type and not a Value type.