C＃委托和lambdas…未指向预期的方法

Question

I'm reading the blog about Y combinators and there's a mention of a snippet of code posted below:

http://blogs.msdn.com/b/wesdyer/archive/2007/02/02/anonymous-recursion-in-c.aspx

Func<int, int> fib = null;
fib = n => n > 1 ? fib(n - 1) + fib(n - 2) : n;
Func<int, int> fibCopy = fib;
Console.WriteLine(fib(6));                        // displays 8
Console.WriteLine(fibCopy(6));                    // displays 8
fib = n => n * 2;
Console.WriteLine(fib(6));                        // displays 12
Console.WriteLine(fibCopy(6));                    // displays 18

Huh!? Notice how the result of calling fib changes and that the result of calling fibCopy differs even from the result of calling fib! (See if you can figure out why)

The poster mentions that this result will occur however, he doesn't mention why and I can't to see to figure it out either. The way I see it is...

fib -> Points to fib sequence lambda
fibCopy -> Points to fib sequence lambda
lambda -> n * 2
fib -> points to new lambda
fibCopy -> points to fib which is pointing to new lambda.... 

but obviously that's not what's going on.

Answer 1

Your explanation is correct.

fibCopy -> points to fib which is pointing to new lambda....

The final fibCopy is still the original definition:

n => n > 1 ? fib(n - 1) + fib(n - 2) : n;

However, fib is no longer recursive, and invoking fibCopy(6) is actually running:

n => n > 1 ? (n - 1) * 2 + (n - 2) * 2 : n