What is the best way to give a C# auto-property an initial value?

Question

How do you give a C# auto-property an initial value?

I either use the constructor, or revert to the old syntax.

Using the Constructor:

Answer 1

Starting with C# 6.0, We can assign default value to auto-implemented properties.

public string Name { get; set; } = "Some Name";

We can also create read-only auto implemented property like:

public string Name { get; } = "Some Name";

See: C# 6: First reactions , Initializers for automatically implemented properties - By Jon Skeet

Answer 2

In addition to the answer already accepted, for the scenario when you want to define a default property as a function of other properties you can use expression body notation on C#6.0 (and higher) for even more elegant and concise constructs like:

public class Person{

    public string FullName  => $"{First} {Last}"; // expression body notation

    public string First { get; set; } = "First";
    public string Last { get; set; } = "Last";
}

You can use the above in the following fashion

    var p = new Person();

    p.FullName; // First Last

    p.First = "Jon";
    p.Last = "Snow";

    p.FullName; // Jon Snow

In order to be able to use the above "=>" notation, the property must be read only, and you do not use the get accessor keyword.

Details on MSDN

Answer 3

private string name;
public string Name 
{
    get 
    {
        if(name == null)
        {
            name = "Default Name";
        }
        return name;
    }
    set
    {
        name = value;
    }
}

Answer 4

In Version of C# (6.0) & greater, you can do :

For Readonly properties

public int ReadOnlyProp => 2;

For both Writable & Readable properties

public string PropTest { get; set; } = "test";

In current Version of C# (7.0), you can do : (The snippet rather displays how you can use expression bodied get/set accessors to make is more compact when using with backing fields)

private string label = "Default Value";

// Expression-bodied get / set accessors.
public string Label
{
   get => label;
   set => this.label = value; 
 }

Answer 5

In C# 6.0 this is a breeze!

You can do it in the Class declaration itself, in the property declaration statements.

public class Coordinate
{ 
    public int X { get; set; } = 34; // get or set auto-property with initializer

    public int Y { get; } = 89;      // read-only auto-property with initializer

    public int Z { get; }            // read-only auto-property with no initializer
                                     // so it has to be initialized from constructor    

    public Coordinate()              // .ctor()
    {
        Z = 42;
    }
}

Answer 6

I think this would do it for ya givng SomeFlag a default of false.

private bool _SomeFlagSet = false;
public bool SomeFlag
{
    get
    {
        if (!_SomeFlagSet)
            SomeFlag = false;        

        return SomeFlag;
    }
    set
    {
        if (!_SomeFlagSet)
            _SomeFlagSet = true;

        SomeFlag = value;        
    }
}