At 9:20 AM -0700 6/29/13, Matt Neuburg wrote:
On Jun 28, 2013, at 5:26 PM, Kyle Sluder <k...@ksluder.com> wrote:
> On Fri, Jun 28, 2013, at 05:17 PM, Matt Neuburg wrote:
Why is the block permitted to assign to the variable sharedInstance
outside the block? Evidently it is because "static" has an effect like
"__block", in that it makes the variable outside the block assignable.
>> But how, exactly? Is it some kind of side effect of being a local static?
>
Consult the blocks spec for more:
> http://clang.llvm.org/docs/BlockLanguageSpec.html
Yes, I looked at the spec and searched on the word "static" but I
can't really understand what the spec is telling me.
Hi Matt,
Thanks for asking the question and getting me to read the spec --
I've been trying to get this straight in my own head as well.
I found this part of the spec pretty readable (it's the minutia about
declarations that makes my eyes glaze over).
What I think you wanted to be searching for is the opposite of
static: "automatic".
The magic 3 paragraphs are:
The compound statement body establishes a new lexical scope within
that of its parent. Variables used within the scope of the compound
statement are bound to the Block in the normal manner with the
exception of those in automatic (stack) storage. Thus one may access
functions and global variables as one would expect, as well as
static local variables.
Local automatic (stack) variables referenced within the compound
statement of a Block are imported and captured by the Block as const
copies. The capture (binding) is performed at the time of the Block
literal expression evaluation.
and
In addition to the new Block type we also introduce a new storage
qualifier, __block, for local variables. The __block storage
qualifier is mutually exclusive to the existing local storage
qualifiers auto, register, and static.
Variables qualified by __block act as if they were in allocated
storage and this storage is automatically recovered after last use
of said variable.
----------------------------
Here's my shot at simple rules:
1) With the exception of automatic (stack-based) variables declared
outside of a block and used within it, everything works the same as
it always has.
2) __block variables act as if all copies of the block (and the
original scope) share a reference to the variable which lives as long
as the last copy.
3) The block's view of all non-__block automatic variables is
read-only and frozen at the time that the block is declared.
----------------------------
I think that's sufficient.
Everything else is either an implementation detail or an optimization
So, to answer your original question: static falls within 1) and
works the way it always has because it's not an automatic variable.
Rather than make this any longer, feel free to poke holes in the
description -- I want to make sure I'm not missing anything.
HTH,
-Steve
_______________________________________________
Cocoa-dev mailing list (Cocoa-dev@lists.apple.com)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com
This email sent to arch...@mail-archive.com
