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Groups > comp.lang.basic.visual.misc > #806
| From | ralph <nt_consulting64@yahoo.net> |
|---|---|
| Newsgroups | comp.lang.basic.visual.misc |
| Subject | Re: What is a class? |
| Date | 2012-02-25 23:03 -0600 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <5odjk75idm6fgl98vbmabap2djd38nvum5@4ax.com> (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> |
On Sat, 25 Feb 2012 22:55:37 -0500, GS <gs@somewhere.net> 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... > >In a procedure: (local scope) >Dim colItems As New Collection >..lives for the entire procedure if not explicitly destroyed beforhand. > ... But you can not "explicitly" destroy the collection object. You can clear the contents but never get rid of the object until the object reference goes out of scope. >In a module: (module scope) >Dim colItems As New Collection >..lives for the duration code executes within the module if not >explicitly destroyed beforhand. > ... but you can not "explicitly" destroy the collection object. You can clear the contents, but you'll never be shed of the object inside the module. >Global scope: >Dim colItems As New Collection >..lives for the entire runtime if not explicitly destroyed beforhand. > ... but (you guessed it <g>) you can not "explicity" destroy the collection object for the life of the program. >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. That is less an issue than all that extra code you have added to your Application every single time you reference the object. Most of the more serious consequences (e.g. memory leaks, circular references, problems on Application exits, etc.) only present themselves in highly specialized circumstances involving specific objects. Thus one can probably program with the "As New" construct for years and never notice a problem or bloat, however it only takes a few wasted hours on tracking down a particular odd behavior of an object to appreciate it is best not to go there in the first place. <g> -ralph
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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
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