November 14, 2010
I wonder if the following is just a misunderstanding on my part or an indicator of an actual problem in D.

The code:

foreach ( i ; 0 .. numberOfThreads ) { threads[i] = new Thread ( ( ) { partialSum ( 1 + i * sliceSize , ( i + 1 ) * sliceSize , delta ) ; } ) ; }

fails to the intended thing, i.e. I had assumed that the created delegates were in fact closures.  However it seems that a delegate simply has a reference to the scope in which it was defined, it doesn't capture the environment.  This means the value of i and sliceSize are always the value when the function is executed not when it is created. I even tried:

 foreach ( i ; 0 .. numberOfThreads ) { immutable id = i ; threads[i] = new Thread ( ( ) { partialSum ( 1 + id * sliceSize , ( id + 1 ) * sliceSize , delta ) ; } ) ; }

and this behaves strangely differently, but it still doesn't work as required, it is still not creating closures.   All the created delegates still share a reference to the same scope.  By trial and error I came up with:

 foreach ( i ; 0 .. numberOfThreads ) {
    void delegate ( ) closedPartialSum ( ) {
      immutable id = i ;
      return ( ) { partialSum ( 1 + id * sliceSize , ( id + 1 ) *
sliceSize , delta ) ; } ;
    }
    threads[i] = new Thread ( closedPartialSum ) ;
  }

and this seems to do the right thing, but this seems like a strange hoop to jump through to create closures.

I guess my question is whether there is any need for delegates that are not closures?  Wouldn't it be simpler to do lexical closures as the only form of delegate?

BTW This is not a problem particular to D, Python has similar issues where Scala, Clojure, Ruby do not.  Groovy is very weird in that what it calls a closure is actually just a code block.

-- 
Russel. ============================================================================= Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder@ekiga.net 41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel@russel.org.uk London SW11 1EN, UK   w: www.russel.org.uk  skype: russel_winder


November 15, 2010
"Russel Winder" <russel@russel.org.uk> wrote in message news:mailman.349.1289736653.21107.digitalmars-d@puremagic.com...


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