Opinions Please - Properties and Constructors

[John F]

Hello All,

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to the
class object by merely setting a property?

The ultimate goal is to have a bunch of objects all containing say a patient
account number (the class does other things, but for sake of argument, the
data component is just patient account) set into a property for later
retrieval.

Thanks,
John

[Miha Markic [MVP C#]]

Hi John,

If data is required at construction time then pass it through constructor.
Otherwise if number of property values isn't known, use properties or some
method which has all required arguments.
The problem with constructor is that you'll have to recreate all of them if
you decide to inherit from base class (and you want all of them).
--
Miha Markic [MVP C#, INETA Country Leader for Slovenia]
RightHand .NET consulting & development www.rthand.com
Blog: http://cs.rthand.com/blogs/blog_with_righthand/
"John F" <[e-mail] in message
news:19**********************************@microsof t.com...

Hello All,

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to
the
class object by merely setting a property?

The ultimate goal is to have a bunch of objects all containing say a
patient
account number (the class does other things, but for sake of argument, the
data component is just patient account) set into a property for later
retrieval.

Thanks,
John

[Chris Dunaway]

Miha Markic [MVP C#] wrote:

Hi John,

If data is required at construction time then pass it through constructor.
Otherwise if number of property values isn't known, use properties or some
method which has all required arguments.
The problem with constructor is that you'll have to recreate all of them if
you decide to inherit from base class (and you want all of them).
--
Miha Markic [MVP C#, INETA Country Leader for Slovenia]
RightHand .NET consulting & development www.rthand.com
Blog: http://cs.rthand.com/blogs/blog_with_righthand/
"John F" <[e-mail] in message
news:19**********************************@microsof t.com...

Hello All,

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to
the
class object by merely setting a property?

The ultimate goal is to have a bunch of objects all containing say a
patient
account number (the class does other things, but for sake of argument, the
data component is just patient account) set into a property for later
retrieval.

Thanks,
John

One reason to use a constructor would be if you want to create an
object but don't want to keep the variable. For example you may want
to add new objects directly to a list:

Dim ListOfObjects As New List(Of SomeClass)

ListOfObjects.Add(New SomeClass("something"))

Or perhaps a method needs to return a new instance of the class based
on parameters:

Public Function CreateAnObject(someString As String, someInteger As
Integer)

Dim something As String

'Do some calculation with the integer or some manipulation of the
string

something = <result of manipulation>

Return New SomeClass(something)

End Function

These are very simplistic examples, but using a constructor can make
the instantiating code easier to read.

In reality, what Miha wrote is correct. If the data is needed to
construct the object then use a constructor. Otherwise, it is entirely
appropriate to instantiate the object and then set the properties
later. Sometimes, you don't know what the properties should be set to
at the time of instantiation so setting the properties later is the
only option.

[Dave Sexton]

Hi John,

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to the
class object by merely setting a property?

<snip>

That depends on whether your class is immutable or supports lazy initialization, sealed or
inheritable, and intricate or simple, and whether construction logic depends on external state.

Immutability must be enforced using constructor arguments and read-only properties. Lazy
initialization can use common constructor arguments for simplicification, but usually has the side
effect of being difficult for inheritance (as mentioned by Miha). Complex construction logic or
construction that depends on external state should probably be encapsulated using the builder
pattern.

--
Dave Sexton

[John F]

Thanks for everyones opinion. It has been very helpful!

"John F" wrote:

Hello All,

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to the
class object by merely setting a property?

The ultimate goal is to have a bunch of objects all containing say a patient
account number (the class does other things, but for sake of argument, the
data component is just patient account) set into a property for later
retrieval.

Thanks,
John

[Arne Vajhøj]

John F wrote:

Is it better to pass 'data' into a class object through a constructor and
then set it as a property internally in that object or is it ok to
instantiate a class object with no parameters and then attach 'data' to the
class object by merely setting a property?

The ultimate goal is to have a bunch of objects all containing say a patient
account number (the class does other things, but for sake of argument, the
data component is just patient account) set into a property for later
retrieval.

For typical data classes I would recommend having both a
no argument constructor and a constructor that sets all
the data.

It gives flexibility in the code. Often the code is
much shorter if you use a constructor with arguments
but in other cases a no argument constructor is
required.

Arne