Compare two instance of a class

[bengamin]

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[The Last Gunslinger]

bengamin wrote:

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

I have been trying to find out the same thing.
From what I can see, if you overrride == in your class then you should
also override Equals, != and GetHashCode.
So that they all exhibit the same behaviour.

Since I might want to test for reference equality in one case and say
check the ID property in another case I would like to override == to
check for ID equality but from what I understand thats not a good idea
as other languages (VB) does not have this operator.

You might want to define an interface that would do a property check on
both instances to determine whether they are equal.

Sorry I cannot be more decisive, I would like to see others views :)

Cheers

--
JB

[richlm]

Recommended practice is that operator "==" and method
"Object.Equals( object)" should behave the same.
If you override Equal you should also override GetHashCode.

You need to bear in mind whether or not you will ever need to compare 2
references (which is the default behaviour) i.e. that refer to the same
instance.

In most cases I think it is better to implement a specific method to compare
reference type instances - value comparison is often a business/application
specific function, and it may be misleading to some developers if you
override default language functionality.

Here's a useful article on MSDN:
http://msdn.microsoft.com/library/de...lsoperator.asp

Richard.

"bengamin" <sa***@langchao .com> wrote in message
news:ea******** ******@tk2msftn gp13.phx.gbl...

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[Razzie]

Sorry but I've gotten curious because of these replies. I don't seem to
understand the question maybe?

I thought what he meant was just that if you have let's say, the following
class:

class A
{
private int _i;

public int i
{
get
{ return this._i; }
set
{ this._i = value; }
}
}

and A a1 = new A(); A a2 = new A();
then a1.i == a2.i would simply return true if they have the same value? That
was the question right? Why would you need to overload the operator for
that?
"richlm" <ri*****@h0tmai 1.com> wrote in message
news:OS******** ******@TK2MSFTN GP10.phx.gbl...

Recommended practice is that operator "==" and method
"Object.Equals( object)" should behave the same.
If you override Equal you should also override GetHashCode.

You need to bear in mind whether or not you will ever need to compare 2
references (which is the default behaviour) i.e. that refer to the same
instance.

In most cases I think it is better to implement a specific method to compare reference type instances - value comparison is often a business/application specific function, and it may be misleading to some developers if you
override default language functionality.

Here's a useful article on MSDN:
http://msdn.microsoft.com/library/de...lsoperator.asp
Richard.

"bengamin" <sa***@langchao .com> wrote in message
news:ea******** ******@tk2msftn gp13.phx.gbl...

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[Marcin Grzêbski]

Hi,

Good practise is to implement "IComparabl e" interface.

int CompareTo(Objec t obj)
- it should return zero if "obj" is equal to base object.

Then you have to (easily) override the "Equals()", as follow:

public override bool Equals(Object obj) {
return (this.CompareTo (obj)==0);
}

Cheers

Marcin

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[Marcin Grzêbski]

Hi Razzie,

Don't you think that there can be more properties than
one or two?

e.g.
// A Person class, that have: FirstName, LastName, Age, Gender.
Person person1=new Person();
Person person2=new Person();

if( person1.FirstNa me==person2.Fir stName
&& person1.LastNam e==person2.Last Name
&& person1.Age==pe rson2.Age
&& person1.Gender= =person2.Gender ) {
//...
}

It looks very complicated. Don't you think?

Regards

Marcin

Sorry but I've gotten curious because of these replies. I don't seem to
understand the question maybe?

I thought what he meant was just that if you have let's say, the following
class:

class A
{
private int _i;

public int i
{
get
{ return this._i; }
set
{ this._i = value; }
}
}

and A a1 = new A(); A a2 = new A();
then a1.i == a2.i would simply return true if they have the same value? That
was the question right? Why would you need to overload the operator for
that?
"richlm" <ri*****@h0tmai 1.com> wrote in message
news:OS******** ******@TK2MSFTN GP10.phx.gbl...

Recommended practice is that operator "==" and method
"Object.Equal s(object)" should behave the same.
If you override Equal you should also override GetHashCode.

You need to bear in mind whether or not you will ever need to compare 2
references (which is the default behaviour) i.e. that refer to the same
instance.

In most cases I think it is better to implement a specific method to

compare

reference type instances - value comparison is often a

business/application

specific function, and it may be misleading to some developers if you
override default language functionality.

Here's a useful article on MSDN:

http://msdn.microsoft.com/library/de...lsoperator.asp

Richard.

"bengamin" <sa***@langchao .com> wrote in message
news:ea****** ********@tk2msf tngp13.phx.gbl. ..

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

== overloading should be the way to go, now according to MSDN you also need
to overload != but nothing more, it saids nothing about Equals or
GetHashCode.

If you overload the default meaning of the == operator you will not longer
compare references , if you want do so you could do it casting both operands
to Object, like this:
(object)instanc e1 == (object) instance2
It should work.

Cheers,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

"The Last Gunslinger" <jb******@yahoo .com> wrote in message
news:6X******** ***********@new s-server.bigpond. net.au...

bengamin wrote:

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

I have been trying to find out the same thing.
From what I can see, if you overrride == in your class then you should
also override Equals, != and GetHashCode.
So that they all exhibit the same behaviour.

Since I might want to test for reference equality in one case and say
check the ID property in another case I would like to override == to
check for ID equality but from what I understand thats not a good idea
as other languages (VB) does not have this operator.

You might want to define an interface that would do a property check on
both instances to determine whether they are equal.

Sorry I cannot be more decisive, I would like to see others views :)

Cheers

--
JB

[Razzie]

ah well, he wrote value and not values... :)

"Marcin Grzêbski" <mg*******@taxu ssi.no.com.spam .pl> wrote in message
news:ce******** *@atlantis.news .tpi.pl...

Hi Razzie,

Don't you think that there can be more properties than
one or two?

e.g.
// A Person class, that have: FirstName, LastName, Age, Gender.
Person person1=new Person();
Person person2=new Person();

if( person1.FirstNa me==person2.Fir stName
&& person1.LastNam e==person2.Last Name
&& person1.Age==pe rson2.Age
&& person1.Gender= =person2.Gender ) {
//...
}

It looks very complicated. Don't you think?

Regards

Marcin

Sorry but I've gotten curious because of these replies. I don't seem to
understand the question maybe?

I thought what he meant was just that if you have let's say, the following class:

class A
{
private int _i;

public int i
{
get
{ return this._i; }
set
{ this._i = value; }
}
}

and A a1 = new A(); A a2 = new A();
then a1.i == a2.i would simply return true if they have the same value? That was the question right? Why would you need to overload the operator for
that?
"richlm" <ri*****@h0tmai 1.com> wrote in message
news:OS******** ******@TK2MSFTN GP10.phx.gbl...

Recommended practice is that operator "==" and method
"Object.Equal s(object)" should behave the same.
If you override Equal you should also override GetHashCode.

You need to bear in mind whether or not you will ever need to compare 2
references (which is the default behaviour) i.e. that refer to the same
instance.

In most cases I think it is better to implement a specific method to

compare

reference type instances - value comparison is often a

business/application

specific function, and it may be misleading to some developers if you
override default language functionality.

Here's a useful article on MSDN:

http://msdn.microsoft.com/library/de...lsoperator.asp

Richard.

"bengamin" <sa***@langchao .com> wrote in message
news:ea****** ********@tk2msf tngp13.phx.gbl. ..

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[bengamin]

Yes, question just as you describe

since i want to build a command function for all class,and i don't know how
to do,so i thought about overload "=="

"Razzie" <ra****@quickne t.nl> дÈëÓʼþ
news:ex******** ******@TK2MSFTN GP12.phx.gbl...

Sorry but I've gotten curious because of these replies. I don't seem to
understand the question maybe?

I thought what he meant was just that if you have let's say, the following
class:

class A
{
private int _i;

public int i
{
get
{ return this._i; }
set
{ this._i = value; }
}
}

and A a1 = new A(); A a2 = new A();
then a1.i == a2.i would simply return true if they have the same value? That was the question right? Why would you need to overload the operator for
that?
"richlm" <ri*****@h0tmai 1.com> wrote in message
news:OS******** ******@TK2MSFTN GP10.phx.gbl...

Recommended practice is that operator "==" and method
"Object.Equals( object)" should behave the same.
If you override Equal you should also override GetHashCode.

You need to bear in mind whether or not you will ever need to compare 2
references (which is the default behaviour) i.e. that refer to the same
instance.

In most cases I think it is better to implement a specific method to

compare

reference type instances - value comparison is often a

business/application

specific function, and it may be misleading to some developers if you
override default language functionality.

Here's a useful article on MSDN:

http://msdn.microsoft.com/library/de...lsoperator.asp

Richard.

"bengamin" <sa***@langchao .com> wrote in message
news:ea******** ******@tk2msftn gp13.phx.gbl...

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.

[bengamin]

Thank you for your help!
Can you give us some example?

"Marcin Grzêbski" <mg*******@taxu ssi.no.com.spam .pl> ????
news:ce******** **@atlantis.new s.tpi.pl...

Hi,

Good practise is to implement "IComparabl e" interface.

int CompareTo(Objec t obj)
- it should return zero if "obj" is equal to base object.

Then you have to (easily) override the "Equals()", as follow:

public override bool Equals(Object obj) {
return (this.CompareTo (obj)==0);
}

Cheers

Marcin

Hi,

I have a C# class and two instance of the class;

the class have some property.

I want to compare the property value of the two instance

How should i do? override == ? use delegate ?

I am sorry ,my english was poor.