When do structs not live on the stack?

Question

I'm reading through Jon Skeet's book reviews and he is going over the numerous inaccuracies of Head First C#.

One of them caught my eye:

[Under Errors Section] Claiming that structs always live on the stack.

In what situations would structs not live on the stack? This goes contrary to what I thought I knew about structs.

Answer 1

One common example is where the struct is a member of an object that is allocated in the heap. There is lots of additional detail in this question here. What’s the difference between struct and class in .Net?

Answer 2

Whenever they are a field on a class

Unusual examples of this:

a: When a value-type variable is captured:

int i = 2;
Action action = delegate {i++;}
action();
Console.WriteLine(i);

This is compiled to something more like:

class Foo {
    public int i;
    public void Bar() {i++;}
}
...
Foo foo = new Foo();
foo.i = 2;
Action action = foo.Bar;
action();
Console.WriteLine(foo.i);

b: When a value-type variable is used in an iterator block:

IEnumerable<int> GetValues() {
   for(int i = 0 ; i < 5 ; i++) yield return i;
}

(the compiler generates a state machine to represent the iterator, of which all local variables (such as i) are fields)