• Mahe <maheweb web.de> Apr 21 2008
• Frits van Bommel <fvbommel REMwOVExCAPSs.nl> Apr 21 2008
• "Steven Schveighoffer" <schveiguy yahoo.com> Apr 21 2008

Mahe <maheweb web.de> writes:

Hi, 
in the following code the statement "b = null" calls "B opAssign( A v )" and
causes an access violation. I don't understand why! How can I set b to null?
I'm using dmd 1.028.

class A
{
	this( int i )
	{
		a = i;
	}
	int a;
}

class B
{
	this( int i )
	{
		a = i;
	}
	int a;
	
	B opAssign( A v )
	{
		a = v.a;
		return this;
	}
}

int main(char[][] args)
{

	A a = new A( 4 );
	assert( a.a == 4 );
	B b ;
	assert( b is null );
	b = new B( 5 );
	b = a;
	assert( b.a == 4 );
	b = null;
	assert( b is null );
}

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

Mahe wrote:
 in the following code the statement "b = null" calls "B opAssign( A v )" and
causes an access violation. I don't understand why! How can I set b to null?
 I'm using dmd 1.028.



Looks like a bug. Please report it here: http://d.puremagic.com/issues/
A workaround is probably to do "b = cast(B) null".

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

"Mahe" wrote
 Hi,
 in the following code the statement "b = null" calls "B opAssign( A v )" 
 and causes an access violation. I don't understand why! How can I set b to 
 null?
 I'm using dmd 1.028.

 class A
 {
 this( int i )
 {
 a = i;
 }
 int a;
 }

 class B
 {
 this( int i )
 {
 a = i;
 }
 int a;

 B opAssign( A v )
 {
 a = v.a;
 return this;
 }
 }

 int main(char[][] args)
 {

 A a = new A( 4 );
 assert( a.a == 4 );
 B b ;
 assert( b is null );
 b = new B( 5 );
 b = a;
 assert( b.a == 4 );
 b = null;
 assert( b is null );
 }


That is interesting... I know that you cannot overload opAssign with 
something that implicitly casts to the lvalue type, but what does the 
compiler do in the case of null?  It casts both to the lvalue type, and 
possibly the argument that is passed to opAssign.

IMO, it should not call opAssign, but set the implicit reference.  I'd file 
it as a bug.

You may be able to workaround by doing:

b = (B)null;

But that seems like a lot of extra work.

-Steve