• Ilya Zaitseff (34/34) Mar 08 2005 This code works:
• xs0 (6/53) Mar 08 2005 You made a mistake - A.this() sets the global b, while "B b=new B()"
• Ilya Zaitseff (25/32) Mar 08 2005 Oops, just a stupid typo :)
• Russ Lewis (16/43) Mar 09 2005 My guess is that the problem is that the delegate you're creating is a
• Ilya Zaitseff (3/41) Mar 10 2005 I got it. Thanks.

"Ilya Zaitseff" <sark7 mail333.com> writes:

This code works:

<code>
import std.stdio;

void delegate () dg;

class A
{
	this() { dg = delegate void () { foo(); }; }
	void foo() { writefln("foo"); }
}

void main()
{
	B b = new B();
	A a = new A();

	dg(); // prints "foo"
}
</code>

But this code throws AV:

<code>
import std.stdio;

class B { void delegate () dg; }

B b;

class A
{
	this() { b.dg = delegate void () { foo(); }; }
	void foo() { writefln("foo"); }
}

void main()
{
	B b = new B();
	A a = new A();

	b.dg(); // AV here
}
</code>

Whats the difference? Is it a bug or specific D behaviour?

xs0 <xs0 xs0.com> writes:

Ilya Zaitseff wrote:
 This code works:
 
 <code>
 import std.stdio;
 
 void delegate () dg;
 
 class A
 {
     this() { dg = delegate void () { foo(); }; }
     void foo() { writefln("foo"); }
 }
 
 void main()
 {
     B b = new B();
     A a = new A();
 
     dg(); // prints "foo"
 }
 </code>
 
 But this code throws AV:
 
 <code>
 import std.stdio;
 
 class B { void delegate () dg; }
 
 B b;
 
 class A
 {
     this() { b.dg = delegate void () { foo(); }; }
     void foo() { writefln("foo"); }
 }
 
 void main()
 {
     B b = new B();
     A a = new A();
 
     b.dg(); // AV here
 }
 </code>
 
 Whats the difference? Is it a bug or specific D behaviour?

You made a mistake - A.this() sets the global b, while "B b=new B()" 
creates the local b.. When you execute b.dg(), it's not the global b, so 
it doesn't have the delegate set, hence AV.. In fact, I'd say that it's 
A.this() that produces AV, because the global b is null...


xs0

"Ilya Zaitseff" <sark7 mail333.com> writes:

On Tue, 08 Mar 2005 18:07:00 +0100, xs0 <xs0 xs0.com> wrote:

 Ilya Zaitseff wrote:
  Whats the difference? Is it a bug or specific D behaviour?

 You made a mistake - A.this() sets the global b, while "B b=new B()"  
 creates the local b.. When you execute b.dg(), it's not the global b, so  
 it doesn't have the delegate set, hence AV.. In fact, I'd say that it's  
 A.this() that produces AV, because the global b is null...

 xs0

Oops, just a stupid typo :)

Actually second code snippet is:

<code>
import std.stdio;

class B
{
   void delegate () dg;
   void run() { dg(); }
}

B b;

class A
{
   this() { b.dg = delegate void () { foo(); }; }
   void foo() { writefln("foo"); }
}

void main()
{
   b = new B();
   A a = new A();
   b.dg(); // prints "foo"
   b.run(); // AV here
}
</code>

bug, isn't it?

Russ Lewis <spamhole-2001-07-16 deming-os.org> writes:

Ilya Zaitseff wrote:
 <code>
 import std.stdio;
 
 class B
 {
   void delegate () dg;
   void run() { dg(); }
 }
 
 B b;
 
 class A
 {
   this() { b.dg = delegate void () { foo(); }; }
   void foo() { writefln("foo"); }
 }
 
 void main()
 {
   b = new B();
   A a = new A();
   b.dg(); // prints "foo"
   b.run(); // AV here
 }
 </code>
 
 bug, isn't it?

My guess is that the problem is that the delegate you're creating is a 
stack delegate, and the stack frame is no longer valid.  Remembery that 
the line
	foo();
in the delegate literal is really
	this.foo();
and that, since this is a stack delegate, the compiler is gettting 
'this' from a function argument which was on the stack; thus, the 
statement really becomes
	stack_frame.this.foo();
where stack_frame is the pointer which is saved in the delegate.  This 
pointer is created when the delegate literal is created, and is invalid 
from the moment that the stack frame (the constructor) exits.

This code should work fine if you change A's constructor to this:
	this() { b.dg = &this.foo; }

"Ilya Zaitseff" <sark7 mail333.com> writes:

On Wed, 09 Mar 2005 11:09:01 -0700, Russ Lewis  
<spamhole-2001-07-16 deming-os.org> wrote:

 Ilya Zaitseff wrote:
 <code>
 import std.stdio;
  class B
 {
   void delegate () dg;
   void run() { dg(); }
 }
  B b;
  class A
 {
   this() { b.dg = delegate void () { foo(); }; }
   void foo() { writefln("foo"); }
 }
  void main()
 {
   b = new B();
   A a = new A();
   b.dg(); // prints "foo"
   b.run(); // AV here
 }
 </code>
  bug, isn't it?

 My guess is that the problem is that the delegate you're creating is a  
 stack delegate, and the stack frame is no longer valid.  Remembery that  
 the line
 	foo();
 in the delegate literal is really
 	this.foo();
 and that, since this is a stack delegate, the compiler is gettting  
 'this' from a function argument which was on the stack; thus, the  
 statement really becomes
 	stack_frame.this.foo();
 where stack_frame is the pointer which is saved in the delegate.  This  
 pointer is created when the delegate literal is created, and is invalid  
 from the moment that the stack frame (the constructor) exits.

 This code should work fine if you change A's constructor to this:
 	this() { b.dg = &this.foo; }

I got it. Thanks.