Why no initial values on {get;set;} accessors (VS 2010 C#)

Question

This must have been asked many times but I cannot find it....sorry...

Why is the following not permitted?

public string MyString = "initial value" {get; private set;}

(Visual C# Express 2010)

Unfortunate that is isn't possible to do presently - but it wouldn't be damaging to add the ability in future C# versions - I hope they do add it in future. (And add the ability to make readonly auto properties) — Mark H, Jul 16 '10 at 15:03
It would be particularly nice if we could flag properties with automatic backing fields to make the backing field `readonly`. At that point, we could initialize through the property but only in the constructor. This has been discussed on SO before. — Steven Sudit, Jul 16 '10 at 15:06
Finally, a feature where VB allows for a more concise syntax! In VB10, `Public Property MyString As String = "initial value"` works. — Heinzi, Jul 16 '10 at 18:02
Possible duplicate of [How do you give a C# Auto-Property a default value?](https://stackoverflow.com/questions/40730/how-do-you-give-a-c-sharp-auto-property-a-default-value) — Heretic Monkey, Jun 13 '19 at 20:48

score 5 · Answer 1 · answered Jul 16 '10 at 14:58

5

It's just not valid syntax. You can't initialize the value of an auto-property, unfortunately.

The best options are to either make the property manually:

private string _MyString = "initial value";
public string MyString { get { return _MyString; } set { _MyString = value; } }

or initialize the value in the constructor:

public string MyString { get; set; }

....

public MyClass() {
    MyString = "initial value";
}

answered Jul 16 '10 at 14:58

MisterZimbu

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I understand there are various ways. I was just wondering why there wasn't a suitable valid syntax (yet). The problem with the above method is the declaration and initalisation are separated, possibly by many, many lines of code, I like @apollodude217 's syntax below – Paulustrious Jan 16 '17 at 20:04

Chuck Callebs · Answer 2 · 2010-07-16T17:25:00.323

2

An alternative:

string _strMyString;

public string MyString
{
    get {
        if (String.IsNullOrEmpty(_strMyString) {
             return "initial value";
        } else { 
             return _strMyString; 
        }
}

edited Jul 16 '10 at 17:25

answered Jul 16 '10 at 14:59

Chuck Callebs

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1

I always forget about that method. – Chuck Callebs Jul 16 '10 at 17:25
3

OrEmpty will break your application when you set it to an empty string. – ctrl-alt-delor Mar 13 '12 at 15:08
Very true. It's left up to the programmer to decide whether that behavior is expected or not. – Chuck Callebs Mar 13 '12 at 19:28

score 1 · Answer 3 · answered Jul 16 '10 at 14:55

1

It's a property, not a field. You can't initialize it this way. Just set the value in the constructor.

answered Jul 16 '10 at 14:55

Steven Sudit

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score 1 · Answer 4 · answered Jul 16 '10 at 15:09

the syntax

public string MyString { get; set; }

is replacing the old style / annoying / trivial (as of vs2008/c# 3.0 you can see all the new features of c# 3.0 here)

private string _MyString;

public string MyString 
{
    get { return _MyString; }
    set { _MyString = value; }
}

the compiler is actually generates a member before compiling your code. you can open a reflector and see the generated member.

score 1 · Answer 5 · answered Jul 16 '10 at 17:56

Why?

I cannot speak on behalf of the designers of C#, but I can make educated speculation:

They wanted to see just how big of a deal it is before taking the time to add another feature and yet another rule to the language.
They could not find a sufficiently elegant-looking way to do this.

That said, here is how I would allow values (when a set accessor is available, of course):

public string MyProp {get;set;} = "initial value"; // not valid C#

Without making the language any more complex, they could write the rule so that it applies to "[all] properties with set accessors" instead of to "default properties with set accessors":

// again, not valid C#:
public string MyProp
{
    get { return _MyProp;}
    set { _MyProp = value; }
} = "initial value before being massaged or rejected by the set accessor.";

The only downside I see here is that it is ugly. The benefits are that you can concisely specify an initial value for a property with that property instead of in the constructor, and that you can let the value be massaged / checked / whatever via constructor at runtime if you wish.

Sorry - not enough 'reputation' to edit my own comments after forgetting CR posts the message. — Paulustrious, Jan 01 '17 at 17:31

score 1 · Accepted Answer · answered Mar 31 '17 at 21:39

1

In VS 2017 you can:

    public int Minimum { get; private set; } = 0;
    public int Maximum { get; set; } = 5;

answered Mar 31 '17 at 21:39

Paulustrious

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Why no initial values on {get;set;} accessors (VS 2010 C#)

6 Answers6