C# 3.0, object initializer and get property returning array, how to initialize?

Question

Having the following class:

public class SomeClass
{
    private readonly int[] _someThings;

    public SomeClass()
    {
        _someThings = new int[4];
    }

    public int[] SomeThings
    {
        get { return _someThings; }
    }
}

How would I use the object initializer syntax to initialize the SomeThings property like in the following (non-working) code extract?

var anObject = new SomeClass
    {
        SomeThings[0] = 4,
        SomeThings[3] = 8
    }

Update

One could do (even without a set property):

anObject.SomeThings[0] = 4;
anObject.SomeThings[3] = 8;

But I'm trying to use the object initializer syntax.

Stefan Steinegger · Accepted Answer · 2009-05-13 15:00:11Z

3

AFAIK, You could only have a Add method like this:

public class SomeClass
{
  void Add(int index, int item) 
  { 
    // ...
  }
}

var anObject = new SomeClass()
    {
        {0, 4}, // Calls Add(0, 4)
        {4, 8}  // Calls Add(4, 8)
    }

answered May 13, 2009 at 15:00

Stefan Steinegger

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Comments

Martin Peck · Accepted Answer · 2009-05-13 14:59:48Z

2

Object Initializer syntax is "syntatic sugar" for setting public properties.

There isn't a public setter for SomeThings, so you can't do it like this.

So, this...

Foo x = new Foo() { Bar = "cheese" };

... is the same as ...

Foo x = new Foo();
x.Bar = "cheese;

... and as such doesn't have any ability to reach into private members to set stuff.

answered May 13, 2009 at 14:59

Martin Peck

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2 Comments

Stécy Over a year ago

You're right, there is no public setter for SomeThings but it does not prevent someone from doing: anObject.SomeThings[0] = 4

Chris Dunaway Over a year ago

Nor should it. But it should prevent you from doing something like this: anObject.SomeThings = new int[5];

Jimmy · Accepted Answer · 2009-05-13 15:02:58Z

0

Theoretically you could do it this way:

var anObject = new SomeClass {
    InitialSomeThings = new[] {
         1,
         2,
         3,
         4
    }
}

class SomeClass {
    private readonly int[] _somethings;
    public int[] 
       get { return _somethings; }
    }

    public int[] InitialSomeThings {
       set { 
           for(int i=0; i<value.Length; i++)
               _somethings[i] = value[i];
       }
   }
}

answered May 13, 2009 at 15:02

Jimmy

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1 Comment

Stefan Steinegger Over a year ago

But you break encapsulation with this InitialSomeThings property setter. This setter should actually not exist.

Mitch Wheat · Accepted Answer · 2009-05-13 15:04:16Z

0

You could add an overloaded constructor:

public class SomeClass
{
    private readonly int[] _someThings;

    public SomeClass()
    {
        _someThings = new int[4];
    }

    public SomeClass(int[] someThings)
    {
        _someThings = someThings;
    }

    public int[] SomeThings
    {
        get { return _someThings; }
    }
}

...

        var anObject = new SomeClass(new [] {4, 8});

answered May 13, 2009 at 15:04

Mitch Wheat

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1 Comment

Stécy Over a year ago

I know :) Maybe the example was a little too simplistic... I was merely trying a way to initialize a property returning an array.

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