Is it possible to initialize a property at the point of declaration

Question

Imagine you have a field _items in a class. You can initialize it at the point of declaration:

class C
{
  IList<string> _items=new List<string>();
}

Now I want to convert this field to an auto generated property, but the initialization is now invalid:

class C
{
  public IList<string> Items=new List<string>(); {get; set;} // Invalid
}

So, I have to do:

class C
{
  public IList<string> Items {get; set;}

  public C
  {
    Items=new List<string>();
  }
}

But this is not nearly as convenient as initializing fields at the point of declaration. Is there a better way to do this, without having to (needlessly) back this property with a private (initialized at the point of declaration) field, for example.

Thanks

possible duplicate of [How do you give a C# Auto-Property a default value?](http://stackoverflow.com/questions/40730/how-do-you-give-a-c-auto-property-a-default-value) — Justin Niessner, Nov 01 '10 at 15:23

Jon Skeet · Accepted Answer · 2014-07-15T12:09:57.097

24

No, automatic properties don't allow you to set an initial value.

It's annoying, but such is life. (It's annoying that they can't be readonly, too. But that's a rant for another day.)

EDIT: Both readonly automatically implemented properties and specifying an initial value are slated to be in C# 6.

edited Jul 15 '14 at 12:09

answered Nov 01 '10 at 15:20

Jon Skeet

1,421,763
867
9,128
9,194

It really is indeed. But let's look at it from the good side. We HAVE auto-get set. That alone makes me happy. – Proclyon Nov 01 '10 at 15:22
1

Yes, I would have *loved* being able to type `IList { get; private set; } = new List();` or something similar. – Fredrik Mörk Nov 01 '10 at 15:32
@Fredrik, that was exactly what I hoped for. Perhaps this would be a good feature to ask for in C# 5? – Michael Goldshteyn Nov 01 '10 at 15:47
@Michael: The C# team is aware that folks including myself would like a bit more control over automatic properties. I'm not personally holding out much hope for seeing it in C# 5, but async/await makes up for it :) – Jon Skeet Nov 01 '10 at 15:50
@T.J.Crowder: Yes, indeed it is... along with read-only automatically implemented properties, pretty much how I've requested them for ages :) – Jon Skeet Jul 15 '14 at 12:02
Found a citation: https://roslyn.codeplex.com/wikipage?title=Language%20Feature%20Status Yay! – T.J. Crowder Jul 15 '14 at 12:05
@T.J.Crowder: Indeed. I'm not going to find and edit every old answer that mentions the state of play when I wrote it though... – Jon Skeet Jul 15 '14 at 12:09
@JonSkeet: No, of course not. :-) I just happened to notice. – T.J. Crowder Jul 15 '14 at 12:11

score 11 · Answer 2 · answered May 18 '17 at 13:54

11

In c#6 you can write something like this:

class C
{
    public IList<string> Items {get; set;} = new List<string>();
}

answered May 18 '17 at 13:54

Martin Slezák

181
2
11

score 1 · Answer 3 · answered Nov 01 '10 at 15:24

I don't believe so - on construction, as you demonstrate, is the next best way so you don't have to use a private backer, and then use constructor-chaining to ensure that the property always gets initialised:

public MyClass() { PropA = default_Value; }
public MyClass(params object[] args) : this() { /* other code */ }

It would be a nice feature; but then, auto implemented properties are there to simplify property implementation on types; and I can't see how you could add, at the language-level, the default-value feature to an auto-property without the code looking a little, well, odd.

But then, that's why I'm not a language designer.

score 1 · Answer 4 · edited May 23 '17 at 12:03

1

I'm afraid it is not possible to directly initialize an auto property when you declare it. And I agree that this is a pity. I don't know any better way then the constructor either. See also Initializing C# auto-properties

edited May 23 '17 at 12:03

Community

1
1

answered Nov 01 '10 at 15:31

treze

3,159
20
21

score 0 · Answer 5 · answered Nov 01 '10 at 15:21

0

Nope, this is the only way.

answered Nov 01 '10 at 15:21

Pieter van Ginkel

29,160
8
71
111

score 0 · Answer 6 · answered Nov 01 '10 at 15:22

0

Since you don't declare the field when you use { get; set; }, you can't specify the initial value.

So you need to declare the field yourself or initialize it in the constructor.

answered Nov 01 '10 at 15:22

Stefan Steinegger

63,782
15
129
193

score 0 · Answer 7 · answered Nov 01 '10 at 15:22

0

Using a private backing field or setting the value in the constructor are the only ways to give initial values to a Property.

answered Nov 01 '10 at 15:22

Justin Niessner

242,243
40
408
536

Is it possible to initialize a property at the point of declaration

7 Answers7