[cfe-dev] "Blocks" in Clang (aka closures)

[David Chisnall]

Thanks Bill,


On 2 Sep 2008, at 17:01, Bill Bumgarner wrote:

> On Sep 2, 2008, at 8:27 AM, David Chisnall wrote:
>> 1) In Seaside (Smalltalk web-app framework) blocks are used as a way
>> of implementing continuation passing.  This requires support for re-
>> binding variables in the closure.  Smalltalk does this via the
>> BlockContext object.  Is there an equivalent of it here?
>
> I'm not familiar with Seaside, so generically...
>
> All local variables are const-copied into the block (if used, of  
> course -- if not, nothing happens) unless marked with __block.
>
> int x = 3;
> __block int y = 4;
>
> ^{
>    // effectively 'const int x;' here
>    x = 4; // error
>    y = 5; // works fine
> };
>
> Global variables work just like they do everywhere else.

I don't think I explained this one properly.  Say I have the block  
you defined here, and I store it somewhere.  Later, I want to reuse  
the block, but have Y point to a different __block-scope variable.   
This pattern is very important for a lot of the stuff that Seeside  
uses to turn a sequence of HTTP requests into something that looks  
like a normal GUI application to the programmer.  The general  
question here is are the blocks reflective, like Smalltalk blocks, or  
are the opaque like GCC nested functions?

David