Does Clone really make a new copy ?

[active]

Console.WriteLi ne(String.Equal s(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

[Tom Shelton]

On Mar 6, 7:58 pm, " active" <activeNOS... @a-znet.comwrote:

Console.WriteLi ne(String.Equal s(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

Actually, no. If you read the docs on string.equals:
true if the value of the value parameter is the same as this instance;
otherwise, false.

Equals on string has been overloaded to return value equality :)

--
Tom Shelton

[Tom Leylan]

It would be important to read the docs on String.Clone() as well. It
doesn't "clone" the string but simply returns another reference. So both
the equality test is True (which one would expect) and the "Is" test is True
(which one would expect wouldn't be the case.)

See: String.Copy() to create a separate object which will pass the equality
test but fail the Is test (demonstrating they aren't the same object.)

"Tom Shelton" <to*********@co mcast.netwrote in message
news:11******** **************@ p10g2000cwp.goo glegroups.com.. .

On Mar 6, 7:58 pm, " active" <activeNOS... @a-znet.comwrote:

>Console.WriteL ine(String.Equa ls(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

Actually, no. If you read the docs on string.equals:
true if the value of the value parameter is the same as this instance;
otherwise, false.

Equals on string has been overloaded to return value equality :)

--
Tom Shelton

[Cor Ligthert [MVP]]

active,

In most cases the Clone creates a "shallow" copy. This means that the clone,
copies only the reference.

In fact does mostly "copy" methods the same. There are 2 kinds of copies.
The shallow copy and the deep copy. The last means copy everything. For the
latter you can mostly use CopyTo, although than you change the object as
well. For a real deep copy you have mostly to serialize and to desterilize.

This is not always consistent in Net, by instance the classes from AdoNet
have another behaviour.

Clone means here copy of an empty object (the same as instancing a new
class, but can be handy if you have created everything yourself without a
strongly typed class)

Copy means here really copy of the total object.

Cor

" active" <ac********** @a-znet.comschreef in bericht
news:%2******** ********@TK2MSF TNGP02.phx.gbl. ..

Console.WriteLi ne(String.Equal s(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

[Tom Shelton]

On Mar 6, 9:21 pm, "Tom Leylan" <tley...@nospam .netwrote:

It would be important to read the docs on String.Clone() as well. It
doesn't "clone" the string but simply returns another reference. So both
the equality test is True (which one would expect) and the "Is" test is True
(which one would expect wouldn't be the case.)

See: String.Copy() to create a separate object which will pass the equality
test but fail the Is test (demonstrating they aren't the same object.)

Very true.

Dim s1 As String = "Hello, world!"
Dim s2 As String = DirectCast(s1.C lone(), String)
MessageBox.Show (String.Format( "s1.Equals( s2) = {0}, s1 Is s2 =
{1}", _
s1.Equals(s2), s1 Is s2))

Dim s3 As String = String.Copy(s1)
MessageBox.Show (String.Format( "s1.Equals( s3) = {0}, s1 Is s3 =
{1}", _
s1.Equals(s3), s1 Is s3))

In both cases, .Equals returns true - but, s1 is not s3 :)

--
Tom Shelton

[active]

Thanks for the help.

But isn't "clone" the wrong word to use for coping a reference?
In the rest of the world doesn't clone mean to make a new item, not a new
name?
Thanks

" active" <ac********** @a-znet.comwrote in message
news:%2******** ********@TK2MSF TNGP02.phx.gbl. ..

Console.WriteLi ne(String.Equal s(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

[active]

"Cor Ligthert [MVP]" <no************ @planet.nlwrote in message
news:uI******** ******@TK2MSFTN GP02.phx.gbl...

active,

In most cases the Clone creates a "shallow" copy. This means that the
clone, copies only the reference.

In fact does mostly "copy" methods the same.

Could you say the above a little differently - I'm not sure what you mean.

[active]

Thanks for the help.

But isn't "clone" the wrong word to use for coping a reference?
In the rest of the world doesn't clone mean to make a new item, not a new
name?
Thanks

[active]

Thanks for the help.

But isn't "clone" the wrong word to use for coping a reference?
In the rest of the world doesn't clone mean to make a new item, not a new
name?
Thanks

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

active wrote:

Console.WriteLi ne(String.Equal s(s, s.Clone.ToStrin g))

s is type string.

This returns True.

If Clone really made a new copy I'd expect False.

Wouldn't you?

The purpose of the Clone method is to create a separate copy of the object.

The String class makes an exception to this and returns a copy of the
reference to itself. As the String class is immutable, it doesn't make
any difference if you get a copy of the reference or a recerence to a copy.

--
Göran Andersson
_____
http://www.guffa.com