class instantiates itself

[=?Utf-8?B?YmlsbCB0aWU=?=]

class Program
{
...
...

static void Main()
{
Program program = new Program();
}
}

- Is it a good practice to have a class instantiate itself?
- What is the rationale for doing it?
- Is Program a quasi singleton?

Thank you.

[Peter Duniho]

Re: class instantiates itself

On Mon, 28 Jul 2008 13:28:08 -0700, bill tie
<billtie@discus sions.microsoft .comwrote:

class Program
{
...
...
>
static void Main()
{
Program program = new Program();
}
}
>
- Is it a good practice to have a class instantiate itself?

That depends on the rest of the design. The basic question of "a class
instantiating itself" is neither good nor bad in and of itself.

- What is the rationale for doing it?

A common example would be if you have a "factory" method in the class
itself, or as you seem to have guessed, have a "singleton" . Another
example might be a data structure where instances create new instances of
itself; cloning, recursive data structures, or other "self-reproducing"
data structures.

- Is Program a quasi singleton?

Define "quasi singleton". It's not my opinion that simply creating an
instance of itself makes a class "singleton-like", but since that is one
part of implementing a singleton, and since you haven't defined the term
"quasi singleton" it's hard to know whether that's enough to justify
calling it that.

Pete

[Andrew Faust]

Re: class instantiates itself



"bill tie" <billtie@discus sions.microsoft .comwrote in message
news:2DD4ADB4-A0D1-4CC9-B601-4B0062EBE930@mi crosoft.com...

class Program
{
...
...
>
static void Main()
{
Program program = new Program();
}
}
>
- Is it a good practice to have a class instantiate itself?

It's not bad practice. There are plenty of reasons to do so. The .Net
framework itself does this in cases. For example look at the IClonable
interface.

Andrew Faust

[=?UTF-8?B?R8O2cmFuIEFuZGVyc3Nvbg==?=]

Re: class instantiates itself

bill tie wrote:

class Program
{
...
...
>
static void Main()
{
Program program = new Program();
}
}
>
- Is it a good practice to have a class instantiate itself?

Yes, if it makes sense for that specific class.

- What is the rationale for doing it?

It's done whenever a method needs to return a new instance of the class.

For example, all the methods in the String class that returns a new
string (Substring, Format, Concat, Replace, ToUpper, ToLower, Insert,
Remove, Trim, et.c.) are creating new instances of the String class.

- Is Program a quasi singleton?

No, it's just a class that it doesn't make sense to create more than one
instance of. If you would eventhough, they would be separate instances.

However, as the program is written to have only one instance of the
class, the person implementing the class might have used short cuts that
depends on this fact, which could cause problems if you would create
more than one instance of it.

--
Göran Andersson
_____

http://www.guffa.com

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

Re: class instantiates itself

On Jul 28, 4:28 pm, bill tie <bill...@discus sions.microsoft .com>
wrote:

class Program
{
  ...
  ...
>
  static void Main()
  {
    Program program = new Program();
  }
>
}
>
- Is it a good practice to have a class instantiate itself?

Of course!!! , it's a VERY common used practice in different pattern,
like Singleton.

- What is the rationale for doing it?

There can be a lot of reasons, a couple of reasons:
1- You do not want the class to have a public constructor (take a look
at the Guid class in the framework) so you expose a method that
returns a created instance
2- The class is non modificable (like string) so each method that
implicate a change returns a new instance.

- Is Program a quasi singleton?

Not really, You can even have a singleton that do not follow this.
but yes, they are related in a way as the singleton usually use this
techinique