• #ponce <nospam nospam.com> Jan 05 2010
• div0 <div0 users.sourceforge.net> Jan 05 2010
• #ponce <nospam nospam.com> Jan 06 2010
• bearophile <bearophileHUGS lycos.com> Jan 07 2010
• bearophile <bearophileHUGS lycos.com> Jan 08 2010

#ponce <nospam nospam.com> writes:

When I started D, it was possible to define a scope class like this.

scope class Something
{
// blah
}

An instance declaration would then _require_ the scope storage class.


{
    scope Something myVar;
   // do something with Something
}

Is there a use case for such a feature.?

div0 <div0 users.sourceforge.net> writes:

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#ponce wrote:
 When I started D, it was possible to define a scope class like this.
 
 scope class Something
 {
 // blah
 }
 
 An instance declaration would then _require_ the scope storage class.
 
 
 {
     scope Something myVar;
    // do something with Something
 }
 
 Is there a use case for such a feature.?


Yes. One of the uses is when you are wrapping some sort of OS resource.

I've got a scope class which I use for file access;
stops you accidentally leaving the file open & locked.

I also use scope classes for storing intermediate results in complex
algorithms when I want deterministic collection. Use scope classes
and it all gets cleaned up when the algorithm finishes.

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
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#ponce <nospam nospam.com> writes:

 Yes. One of the uses is when you are wrapping some sort of OS resource.
 
 I've got a scope class which I use for file access;
 stops you accidentally leaving the file open & locked.
 
 I also use scope classes for storing intermediate results in complex
 algorithms when I want deterministic collection. Use scope classes
 and it all gets cleaned up when the algorithm finishes.
 


OK, makes sense now.

Neat feature indeed.

bearophile <bearophileHUGS lycos.com> writes:

div0:
 I also use scope classes for storing intermediate results in complex
 algorithms when I want deterministic collection. Use scope classes
 and it all gets cleaned up when the algorithm finishes.


Currently scopes objects can be useful as a performance optimization too. They
(when possible) get allocated on the stack, and avoiding heap allocations in D
is currently very advantageous because the GC is currently slow (compared to
modern GCs you can find in Java).

And time ago I've said to LDC developers that there is another way to further
optimize the deallocation of such stack-allocated objects (improving the
deallocation code), so in future their performance will hopefully further
improve a little.

Bye,
bearophile

bearophile <bearophileHUGS lycos.com> writes:

 Currently scopes objects can...


What I have said is about scoped objects, while you were talking about scoped
classes, a feature I didn't even remember about. Sorry :-)

Bye,
bearophile