Overriding == and testing to null

[EL OSO]

Hi, let's suppose I have a

class A
{
int x;
...
public static bool operator == (A a1 , A a2)
{
return (a1.x==a2.x);
}
}

But, outside the class, I have a problem when I try to test a probably not
initialized class.
For instance, think about this code:
public void myFunc()
{
A a1;
A a2;
.....
if (a1 == null)
{
//some null value handling
}
....
}

The problem is that testing a1==null creates recursive calls to the operator
== of class A.
How do I test if something is null without having to invoke the == operator
for that "something"?
Tnx in advance.

[EL OSO]

Dumb of me, I mixed two questions.
What I was trying to say is that the invoked operator == for class A creates
a null reference when it tries to access a2.x when a2 is null (as I wrote on
MyFunc)

I tried in the definition of operator == something like
if (a1==null) or (a2==null)
return false
else
return (a1.x == (a2.x)

BUT, comparing a1 == null creates the recursive call to operator == in class
A

Do I make myself more clear this time? :p

"EL OSO" <no***@nospam.com> escribió en el mensaje
news:Oa**************@TK2MSFTNGP09.phx.gbl...

Hi, let's suppose I have a

class A
{
int x;
...
public static bool operator == (A a1 , A a2)
{
return (a1.x==a2.x);
}
}

But, outside the class, I have a problem when I try to test a probably not
initialized class.
For instance, think about this code:
public void myFunc()
{
A a1;
A a2;
....
if (a1 == null)
{
//some null value handling
}
...
}

The problem is that testing a1==null creates recursive calls to the operator == of class A.
How do I test if something is null without having to invoke the == operator for that "something"?
Tnx in advance.

[Mattias Sjögren]

BUT, comparing a1 == null creates the recursive call to operator == in class
A

Cast to object first to prevent that.

if ( (object)a1 == null )

Mattias

--
Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Helge Jensen]

EL OSO wrote:

I tried in the definition of operator == something like
if (a1==null) or (a2==null)
return false
else
return (a1.x == (a2.x)
That's not really what you want, is it, if (object)a1 == null &&
(object)a2 == null ;)

I use the pattern:

public static bool operator==(A a1, A a2) {
if ( (object)a1 == null )
return (object)a2 == null;
else if ((object)a2 == null)
return false;
else
return a1.x == a2.x
}
BUT, comparing a1 == null creates the recursive call to operator == in class
A
Yes, you just overloaded operator==(A,A), so that gets called to compare
a1 and null.

The "trick" is to make a1 staticly typed as something that compares by
reference with operator==: object.
Do I make myself more clear this time? :p

mostly,... I'm not that good at being clear myself.

--
Helge Jensen
mailto:he**********@slog.dk
sip:he**********@slog.dk
-=> Sebastian cover-music: http://ungdomshus.nu <=-

[Ted Miller]

You could use object.ReferenceEquals().

"EL OSO" <no***@nospam.com> wrote in message
news:Oa**************@TK2MSFTNGP09.phx.gbl...

Hi, let's suppose I have a

class A
{
int x;
...
public static bool operator == (A a1 , A a2)
{
return (a1.x==a2.x);
}
}

But, outside the class, I have a problem when I try to test a probably not
initialized class.
For instance, think about this code:
public void myFunc()
{
A a1;
A a2;
....
if (a1 == null)
{
//some null value handling
}
...
}

The problem is that testing a1==null creates recursive calls to the
operator
== of class A.
How do I test if something is null without having to invoke the ==
operator
for that "something"?
Tnx in advance.