这里发生了什么?如果没有默认的构造函数,如何调用它?

给出以下代码:

public struct Foo
{
    public Foo(int bar, int baz) : this()
    {
        Bar = bar; // Err 1, 2
        Baz = baz; // Err 3
    }

    public int Bar { get; private set; }
    public int Baz { get; private set; }
}

什么? : this() 事实上呢?没有默认的构造函数,所以它调用什么?如果没有这个附录,整个事情就会因错误而崩溃。

Error   1   The 'this' object cannot be used before all of its fields are assigned to
Error   2   Backing field for automatically implemented property 'Foo.Bar' must be fully assigned before control is returned to the caller. Consider calling the default constructor from a constructor initializer.
Error   3   Backing field for automatically implemented property 'Foo.Baz' must be fully assigned before control is returned to the caller. Consider calling the default constructor from a constructor initializer.