On Mon, Jan 24, 2011 at 11:13 AM, Joshua Ballanco <
jballanc@gmail.com> wrote:
Regarding the potential bug...well...where to begin? So, yes, MacRuby blocks
have the same semantics as regular Ruby blocks, *except* when they are
dispatched through GCD. In that case, ivars are shared, but local variable
get copied. I'm sure Laurent can explain why better than I, but it has to do
with the semantics of libdispatch and the uncertainty inherent in when a
dispatched block or function will execute (i.e. if local variables were not
copied during dispatch, they might go out of scope and be collected before
GCD ever gets around to running the code).
Wow, that's very surprising. I'm not sure I agree with bending Ruby
semantics so drastically, even to help concurrency. Or at least, I'd
expect other threaded scenarios to be consistent:
~ ➔ ruby -ve "a = 0; Thread.new { a += 1 }.join; p a"
MacRuby 0.8 (ruby 1.9.2) [universal-darwin10.0, x86_64]
1
~ ➔ ruby -ve "a = 0; q = Dispatch::Queue.concurrent; q.sync {a += 1}; p a"
MacRuby 0.8 (ruby 1.9.2) [universal-darwin10.0, x86_64]
0
The implicitness in being able to mutate the surrounding scope is
certainly problematic. This is one reason Java's anonymous inner
classes require that referenced variables be declared final...to
indicate they can't be mutated by the body of the anonymous inner
class's methods.
The result is that people end up using one-element arrays and the
like, but people find ways around anything.
So I suppose this applies to anything in the surrounding scope,
including visibility, $~, and so on?