Why does this not compile?

[Steven Schveighoffer]

On 3/6/18 9:42 AM, Shachar Shemesh wrote:

> I fail to see any reasoning[1] that disallows the former but allows the 
> later.
> 
> 
> 1 - That is obviously not true. I see the reasoning all too well. Static 
> vars are like globals, and you're not getting to them via the struct's 
> instance. I would argue that, as far as the programmer, however, there 
> is no difference. There is no semantic difference between allowing the 
> first and not the second.

These aren't globals or static, they are no different than pointers 
(which is actually what they are).

Here is the problem with option 2: If you have a struct that is 
immutable (or shared), it can be passed without problems to another 
thread. If you can then start mucking with local variables in another 
thread with the assumption that they are thread-local, then you have 
broken the guarantee of immutable or shared. Even const can cause problems.

static data is different, in that it is either shared or thread-local, 
and then the path forward is quite clear. Passing thread-local data to 
another thread as if it were local to the recipient is like __gshared, 
and shouldn't be so easy to do.

-Steve