Solved

qoy (i do not have that many points :-)

Posted on 2002-06-16
10
132 Views
Last Modified: 2010-04-04
Could a private constructor be useful for a Delphi object? Describe a constallation.
What is the problem of Delphi 5 (maybe also 4 and 6) with a private constructor?

100 points for an answer to both parts. 50 for one part.
No sample code required. A good explanation is enough.
Maybe more points for a good description.
0
Comment
Question by:robert_marquardt
  • 4
  • 3
  • 3
10 Comments
 
LVL 27

Expert Comment

by:kretzschmar
ID: 7083126
qoy->question of the year?

never used a private constructor,
no idea whats thebenefit of of ths

listening . . .

meikl ;-)
0
 
LVL 11

Author Comment

by:robert_marquardt
ID: 7083177
To precise the question: ONLY a private constructor!
Yes, it IS useful.
0
 
LVL 17

Accepted Solution

by:
geobul earned 200 total points
ID: 7083193
Hi,
Nice question, Robert.

I've never used it before but made some tests. And the tests show that:
1. if the object is created in the same unit then the private constructor is executed.
2. if the object is created outside its unit then the inherited constructor is used instead.

So, the conclusion:
A private constructor could be useful for an object which is used by another object in the same unit to perform some special operations (initialization) which are specific to that second (master) object and are not mandatory when the first object is used by itself.

Is that clear enough (understandable)? Does that make sense?

Regards, Geo
0
 
LVL 17

Expert Comment

by:geobul
ID: 7083217
About your second question: I can't find out any problems using private constructors in Delphi 5. What did you have in mind?
0
 
LVL 11

Author Comment

by:robert_marquardt
ID: 7083268
geobul, almost there.
1. not bad, but i have a more useful task implemented already
2. you mentioned the problem, but failed to recognize it.
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 11

Author Comment

by:robert_marquardt
ID: 7088984
I will solve the question tomorrow.
0
 
LVL 27

Expert Comment

by:kretzschmar
ID: 7089016
yep, do it :-)
0
 
LVL 11

Author Comment

by:robert_marquardt
ID: 7091834
I use a private constructor as geobul mentioned. A controller object (component) creates them. The objects itself represent USB devices. No user interference is needed because the devices are plugged and as reaction a device object is created. A user/program created object is not advisable here because a 1 : 1 representation is always needed. For that i wanted to make it impossible to create a device object.

The problem is mentioned by geobul as 2. The TObject.Create is not hidden because it is a static method not a virtual method.
This i consider as a language problem. Visibility clashes with inheritance.
Locally the private constructor hides the TObject.Create. Externally TObject.Create is still visible.
I also get no visibility warning like for virtual methods. So the most difficult to understand language part is completely unvocered by hints or warnings.

I will award geobul the 100 points. Maybe more. It was a really tricky question.
0
 
LVL 27

Expert Comment

by:kretzschmar
ID: 7092386
aplause ;-)
0
 
LVL 17

Expert Comment

by:geobul
ID: 7092527
Wow, so many many thanks, Robert :-)))

I see what you had in mind now. On the one hand that is some kind of flexibility but on the other hand the lack of warning messages is really bad. This may lead to very-hard-to-find errors.

Thank you again and best regards, Geo
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
This Micro Tutorial hows how you can integrate  Mac OSX to a Windows Active Directory Domain. Apple has made it easy to allow users to bind their macs to a windows domain with relative ease. The following video show how to bind OSX Mavericks to …
In this video I am going to show you how to back up and restore Office 365 mailboxes using CodeTwo Backup for Office 365. Learn more about the tool used in this video here: http://www.codetwo.com/backup-for-office-365/ (http://www.codetwo.com/ba…

867 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now