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digitalmars.D.learn - Does the 'with' statement affect object lifetime?

reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
Is the following code legal for a class?

class C {
     int i;
}

void main() {
     with(new C()) {
         i = 42; // <-- Is the anonymous object alive at this point?
     }
}

The object seems to live long enough for a class. That's probably 
because the garbage collector kicks in late. But consider the same code 
with a struct:

import std.stdio;

struct S {
     int i;

     this(int i = 0)
     {
         writeln("constructed");
     }

     ~this()
     {
         writeln("destructed");
     }
}

void main() {
     with(S(1)) {
         writeln("inside 'with' statement");
         i = 42; // <-- Is the anonymous object alive at this point?
     }
}

The output indicates that the anonymous object is destroyed before the 
body of the with is executed:

constructed
destructed
inside 'with' statement

This contradicts with with's spec:

   http://dlang.org/statement.html#WithStatement

It says that


with (expression)
{
   ...
   ident;
}

is semantically equivalent to:
{
   Object tmp;
   tmp = expression;
   ...
   tmp.ident;
}

Bug?

Ali

-- 
D Programming Language Tutorial: http://ddili.org/ders/d.en/index.html
Jun 19 2012
next sibling parent reply =?UTF-8?B?QWxleCBSw7hubmUgUGV0ZXJzZW4=?= <alex lycus.org> writes:
On 19-06-2012 19:51, Ali Çehreli wrote:

 Is the following code legal for a class?

 class C {
 int i;
 }

 void main() {
 with(new C()) {
 i = 42; // <-- Is the anonymous object alive at this point?
 }
 }

 The object seems to live long enough for a class. That's probably
 because the garbage collector kicks in late. But consider the same code
 with a struct:

 import std.stdio;

 struct S {
 int i;

 this(int i = 0)
 {
 writeln("constructed");
 }

 ~this()
 {
 writeln("destructed");
 }
 }

 void main() {
 with(S(1)) {
 writeln("inside 'with' statement");
 i = 42; // <-- Is the anonymous object alive at this point?
 }
 }

 The output indicates that the anonymous object is destroyed before the
 body of the with is executed:

 constructed
 destructed
 inside 'with' statement

 This contradicts with with's spec:

 http://dlang.org/statement.html#WithStatement

 It says that


 with (expression)
 {
 ...
 ident;
 }

 is semantically equivalent to:
 {
 Object tmp;
 tmp = expression;
 ...
 tmp.ident;
 }

 Bug?

 Ali


I say bug.

BTW, the reason the class reference is alive is because it's on the 
stack. Regardless of whether you're using with, it wouldn't be collected 
by the GC until the current stack frame exits.

-- 
Alex Rønne Petersen
alex lycus.org
http://lycus.org
Jun 19 2012
parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 06/19/2012 10:56 AM, Alex Rønne Petersen wrote:


 BTW, the reason the class reference is alive is because it's on the
 stack. Regardless of whether you're using with, it wouldn't be collected
 by the GC until the current stack frame exits.


Ah... Good point.

Here is the bug report:

   http://d.puremagic.com/issues/show_bug.cgi?id=8269

Ali
Jun 19 2012
prev sibling parent Timon Gehr <timon.gehr gmx.ch> writes:
On 06/19/2012 07:51 PM, Ali Çehreli wrote:

 Bug?


Bug.
Jun 19 2012