Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.basic.visual.misc > #804
| From | "Auric__" <not.my.real@email.address> |
|---|---|
| Newsgroups | comp.lang.basic.visual.misc |
| Subject | Re: What is a class? |
| Date | 2012-02-26 04:41 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <XnsA004DCAD42831auricauricauricauric@88.198.244.100> (permalink) |
| References | (3 earlier) <XnsA00492FC86A25auricauricauricauric@88.198.244.100> <m_WdnZ1BdOYv6NTSnZ2dnUVZ_jydnZ2d@giganews.com> <XnsA004CD148B656auricauricauricauric@88.198.244.100> <cLCdnTOc3IH0NdTSnZ2dnUVZ_tudnZ2d@giganews.com> <jicag2$87f$1@dont-email.me> |
GS wrote:
> Jim Mack wrote :
>>> Jim Mack wrote:
>>>
>>>>> Dim duck As monster
>>>>> Set duck = New monster
>>>>>
>>>>> "Dim duck As New monster" is essentially the same thing as the above
>>>>> 2 lines.
>>>>
>>>> For the purpose of this discussion, maybe. But "Dim As New" is
>>>> frowned on because it adds an implicit 'is nothing' check on every
>>>> reference to the object, and you lose control over the object
>>>> lifetime.
>>>
>>> Interesting. First I've heard of it (but then, I don't use VB very
>>> much any more, and can't recall having ever used VB for "serious" OOP).
>>>
>>> Is this documented anywhere? Help file, MSDN, whatever?
>>
>> The help files do mention it, but obliquely. What is said (from memory)
>> is that when you 'Dim As New' the object is not immediately created, as
>> it would be if you did a Dim followed by a Set = New, but rather is
>> instantiated on first reference.
>>
>> The obvious question is, how does it know which is the first reference?
>> It knows that because _every_ reference contains a check to see if it's
>> been created yet -- the implicit 'is nothing' check I mentioned.
>>
>> What follows from that is that you can't then legitimately test "If x
>> Is Nothing" yourself, because doing so references X, and so creates
>> it... that's how you lose (some) control over object lifetime.
>
> I thought that the object created by "Dim As New" existed until the
> exit from the scope they were created in. So...
[snip]
I read that as meaning you lose control over when the object is *created*,
i.e. initialized. I noticed this before Jim posted, while stepping through
my "monster" class -- the Class_Initialize code wasn't called until "duck"
attacked "dragon"...
Dim duck As New monster, dragon As New monster
duck.Attack dragon 'both get initialized right before .Attack
-----vs-----
Dim duck As monster, dragon As monster
Set duck = New monster 'duck gets initialized here
Set dragon = New monster 'dragon gets initialized here
duck.Attack dragon
but I didn't really give it any thought.
> Also, I've created objects in this manner, tested them other than "If
> colItems Is Nothing" via ways like "If colItems.Count > 0" so I know if
> the created instance exists. Also, creating a new instance by using "If
> colItems Is Nothing" doesn't cause any problems when you access its
> items later, indicating VB is not at all confused about which
> 'instance' you're referring to.
Here's what the VB5CCE helpfile says about Dim As New:
Keyword that enables implicit creation of an object. If you use New when
declaring the object variable, a new instance of the object is created on
first reference to it, so you don't have to use the Set statement to
assign the object reference.
Based on *that*, I would use Dim As New, but based on what Jim says, Dim:
Set = New would probably give slightly better performance.
...okay, *very* slight. I just tried this code:
f! = Timer
For L0& = 1 To 1000000
Set duck = New monster 'duck gets initialized here
Set dragon = New monster 'dragon gets initialized here
duck.mName = "duck"
dragon.mName = "dragon"
duck.Attack dragon
Set duck = Nothing
Set dragon = Nothing
Next L0&
g! = Timer
...first using Dim As: Set = New, then using Dim As New. The total
difference between the two runs on my machine is only about .06 seconds
more for Dim As New (9.00... seconds vs 9.06... seconds), which is
negligible when averaged out over 1,000,000 iterations.
Of course, this is a trivial example, but in any project that doesn't
specifically need to check if an object Is Nothing, I see no reason not to
use Dim As New. The additional checks add such little overhead that I don't
think I'd be worried about it.
--
Unreal uses the Super Mario Bros. engine.
Back to comp.lang.basic.visual.misc | Previous | Next — Previous in thread | Next in thread | Find similar
What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-24 04:02 -0800
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-24 14:06 +0000
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-25 03:07 -0800
Re: What is a class? Helmut_Meukel <Helmut_Meukel@bn-hof.invalid> - 2012-02-25 14:19 +0100
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-25 21:26 +0000
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-25 18:58 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-25 19:39 -0500
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-26 03:09 +0000
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-25 22:35 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-25 22:55 -0500
Re: What is a class? "Farnsworth" <nospam@nospam.com> - 2012-02-25 23:27 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-26 01:30 -0500
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-26 04:41 +0000
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-25 23:05 -0600
Re: What is a class? "Henning" <computer_hero@coldmail.com> - 2012-02-26 11:24 +0100
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-25 23:03 -0600
Re: What is a class? GS <gs@somewhere.net> - 2012-02-26 01:26 -0500
Re: What is a class? "Stuart McCall" <smccall@myunrealbox.com> - 2012-02-27 04:15 +0000
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-27 00:48 -0600
Re: What is a class? "Mayayana" <mayayana@invalid.nospam> - 2012-02-27 08:57 -0500
Re: What is a class? "Stuart McCall" <smccall@myunrealbox.com> - 2012-02-27 19:19 +0000
Re: What is a class? "Stuart McCall" <smccall@myunrealbox.com> - 2012-02-27 19:12 +0000
Re: What is a class? "Bob Butler" <bob_butler@cox.invalid> - 2012-02-27 06:06 -0800
Re: What is a class? "Stuart McCall" <smccall@myunrealbox.com> - 2012-02-27 19:24 +0000
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 11:01 -0500
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-27 11:07 -0600
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 13:10 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-27 19:09 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 13:29 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 14:43 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-27 22:14 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 16:45 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 18:23 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-27 23:26 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-28 13:54 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-28 08:37 -0500
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-28 09:19 -0600
Re: What is a class? GS <gs@somewhere.net> - 2012-02-28 10:42 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-29 06:47 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-29 09:39 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-29 13:33 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-29 14:43 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-29 21:39 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-29 16:15 -0500
Re: What is a class? Schmidt <sss@online.de> - 2012-02-29 23:20 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-28 00:16 -0500
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-27 13:26 -0500
Re: What is a class? "Stuart McCall" <smccall@myunrealbox.com> - 2012-02-27 19:33 +0000
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-27 15:50 -0500
Re: What is a class? Helmut_Meukel <Helmut_Meukel@bn-hof.invalid> - 2012-02-26 11:02 +0100
Re: What is a class? GS <gs@somewhere.net> - 2012-02-26 14:23 -0500
Re: What is a class? GS <gs@somewhere.net> - 2012-02-26 17:09 -0500
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-25 22:21 -0600
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-26 04:51 +0000
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-25 23:10 -0600
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-26 04:11 -0800
Re: What is a class? Helmut_Meukel <Helmut_Meukel@bn-hof.invalid> - 2012-02-26 16:37 +0100
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-26 18:36 +0000
Re: What is a class? ralph <nt_consulting64@yahoo.net> - 2012-02-26 14:11 -0600
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-27 03:11 -0800
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-27 16:33 +0000
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-27 13:33 -0500
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-28 04:07 -0800
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-25 03:33 -0800
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-25 04:19 -0800
Re: What is a class? "Ivar" <ivar.ekstromer000@ntlworld.com> - 2012-02-24 15:15 +0000
Re: What is a class? GS <gs@somewhere.net> - 2012-02-24 14:52 -0500
Re: What is a class? "Ivar" <ivar.ekstromer000@ntlworld.com> - 2012-02-24 23:10 +0000
Re: What is a class? GS <gs@somewhere.net> - 2012-02-24 19:46 -0500
Re: What is a class Way off Topic "Ivar" <ivar.ekstromer000@ntlworld.com> - 2012-02-25 02:20 +0000
Re: What is a class Way off Topic GS <gs@somewhere.net> - 2012-02-25 16:57 -0500
Re: What is a class? Helmut_Meukel <Helmut_Meukel@bn-hof.invalid> - 2012-02-25 11:36 +0100
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-25 03:35 -0800
Re: What is a class? Jim Mack <no-uce-ube@mdxi.com> - 2012-02-24 15:23 -0500
Re: What is a class? "Auric__" <not.my.real@email.address> - 2012-02-25 01:33 +0000
Re: What is a class? Peter Nolan <peter.nolan40@gmail.com> - 2012-02-25 03:09 -0800
Re: What is a class? "Mayayana" <mayayana@invalid.nospam> - 2012-02-24 20:05 -0500
csiph-web