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digitalmars.D.learn - What does 'scope' mean for non-class types?

reply "Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:
In D2, what is the effect (if any) of 'scope' in the following situations?

  scope int a;

  struct B { ... }
  scope B b;

  scope int[] c;

  // According to the spec, 'in' is shorthand for 'const scope'.
  void foo(in char[] d) { ... }


Thanks,
-Lars
May 29 2010
next sibling parent bearophile <bearophileHUGS lycos.com> writes:
Lars T. Kyllingstad:

 In D2, what is the effect (if any) of 'scope' in the following situations?


I think, it's just sloppiness of the compiler. I have reported similar things
in a bug report time ago, bug 3934. If the things you have found are missing in
that bug report, you can add them.

Bye,
bearophile
May 29 2010
prev sibling parent reply div0 <div0 users.sourceforge.net> writes:
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Lars T. Kyllingstad wrote:

 In D2, what is the effect (if any) of 'scope' in the following situations?
 
   scope int a;


Nothing


 
   struct B { ... }
   scope B b;


Nothing, B's destructor will be called even without scope.


 
   scope int[] c;


c gets deleted when the scope ends. this applies to classes as well.


 
   // According to the spec, 'in' is shorthand for 'const scope'.
   void foo(in char[] d) { ... }


d is const (read only).
I've no idea why scope is mentioned, it's meaningless in the context
of function arguments.

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
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May 29 2010
next sibling parent reply Don <nospam nospam.com> writes:
div0 wrote:

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 Lars T. Kyllingstad wrote:

 In D2, what is the effect (if any) of 'scope' in the following situations?

   scope int a;


 
 Nothing
 

   struct B { ... }
   scope B b;


 
 Nothing, B's destructor will be called even without scope.
 

   scope int[] c;


 
 c gets deleted when the scope ends. this applies to classes as well.
 

   // According to the spec, 'in' is shorthand for 'const scope'.
   void foo(in char[] d) { ... }


 
 d is const (read only).
 I've no idea why scope is mentioned, it's meaningless in the context
 of function arguments.


I think in one of the early, complicated versions of the const system, 
it meant something. Looks like this mention of it was accidentally left 
in the spec.
May 29 2010
parent reply "Lars T. Kyllingstad" <public kyllingen.NOSPAMnet> writes:
On Sun, 30 May 2010 08:15:50 +0200, Don wrote:


 div0 wrote:

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 Lars T. Kyllingstad wrote:




[...]


   // According to the spec, 'in' is shorthand for 'const scope'. void
   foo(in char[] d) { ... }


 
 d is const (read only).
 I've no idea why scope is mentioned, it's meaningless in the context of
 function arguments.


 
 I think in one of the early, complicated versions of the const system,
 it meant something. Looks like this mention of it was accidentally left
 in the spec.


So in the context of function arguments, 'in' is just a synonym for 
'const'?  It seems to me like it should be removed from the language, 
then.

-Lars
May 30 2010
parent bearophile <bearophileHUGS lycos.com> writes:
Lars T. Kyllingstad:

 So in the context of function arguments, 'in' is just a synonym for 
 'const'?  It seems to me like it should be removed from the language, 
 then.


http://d.puremagic.com/issues/show_bug.cgi?id=3943.

Bye,
bearophile
May 30 2010
prev sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
div0 wrote:

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 Lars T. Kyllingstad wrote:

 In D2, what is the effect (if any) of 'scope' in the following situations?

   scope int a;


 
 Nothing


http://www.digitalmars.com/d/2.0/attribute.html#scope
"This means that the destructor for an object is automatically called 
when the reference to it goes out of scope."
So there are two ways to interpret this:

- primitive types don't have destructors, so it shouldn't compile

- the destructor of a primitive type is nop, so the reason it has no 
effect at the moment is
http://d.puremagic.com/issues/show_bug.cgi?id=2483


   struct B { ... }
   scope B b;


 
 Nothing, B's destructor will be called even without scope.
 

   scope int[] c;


 
 c gets deleted when the scope ends. this applies to classes as well.


<snip>

What gets deleted - the array or the individual objects?

Stewart.
May 30 2010
parent reply div0 <div0 users.sourceforge.net> writes:
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Stewart Gordon wrote:

 div0 wrote:

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 Lars T. Kyllingstad wrote:

 In D2, what is the effect (if any) of 'scope' in the following
 situations?

   scope int a;


 Nothing


 
 http://www.digitalmars.com/d/2.0/attribute.html#scope
 "This means that the destructor for an object is automatically called
 when the reference to it goes out of scope."
 So there are two ways to interpret this:
 
 - primitive types don't have destructors, so it shouldn't compile
 
 - the destructor of a primitive type is nop, 


Meh. I don't really care either which way, though perhaps for the sake
of writing template code it should continue to be allowed as a nop.


 so the reason it has no effect at the moment is
 http://d.puremagic.com/issues/show_bug.cgi?id=2483


No, that bug is completely different.
None of Lars example code involved assigning to a scope var after it's
declaration. We've discussed this before; allowing assignment to a scope
variable raise questions about which object should actually be deleted.


 

   struct B { ... }
   scope B b;


 Nothing, B's destructor will be called even without scope.


   scope int[] c;


 c gets deleted when the scope ends. this applies to classes as well.


 <snip>
 
 What gets deleted - the array or the individual objects?
 
 Stewart.


Just the array. There maybe references to those objects elsewhere.
Though if the compiler can do escape analysis and prove all the objects
are dead, then they should be deleted at end of scope as well.

- --
My enormous talent is exceeded only by my outrageous laziness.
http://www.ssTk.co.uk
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May 30 2010
parent Stewart Gordon <smjg_1998 yahoo.com> writes:
div0 wrote:
<snip>

 No, that bug is completely different.
 None of Lars example code involved assigning to a scope var after it's
 declaration. We've discussed this before; allowing assignment to a scope
 variable raise questions about which object should actually be deleted.


True, but you stated before that scope on a primitive type does 
_nothing_ effect, so I was just pointing out that by spec that isn't 
literally the case.


   struct B { ... }
   scope B b;


 Nothing, B's destructor will be called even without scope.


   scope int[] c;


 c gets deleted when the scope ends. this applies to classes as well.


 <snip>

 What gets deleted - the array or the individual objects?

 Stewart.


 
 Just the array. There maybe references to those objects elsewhere.
 Though if the compiler can do escape analysis and prove all the objects
 are dead, then they should be deleted at end of scope as well.


But you might also want to create an array of RAII objects.

At the moment, you can't have an array of a scope class, and if you want 
an array of RAII objects you have to declare each individually and then 
put them into the array (meaning there can only be a fixed number of them).

Stewart.
Jun 01 2010