Question

It’s possible in C# to write things such way:

Instrument instr = new Instrument { ClassCode = "Hello", Ticker = "World" };

However to do that you have to add set; in the corresponding class:

class Instrument
{
    public string ClassCode { get; set; }
    public string Ticker { get; set; }
}

This means that later someone can accidentally change value:

instr.ClassCode.set = "Destroy"

And I don’t want to allow that. I.e., from one hand I want a readonly property, from another hand i want to create objects like that:

Instrument instr = new Instrument { ClassCode = "Hello", Ticker = "World" };

I’m not sure if this is possible. Probably I should use fields or something else instead of properties. I only want to have the syntax of the last sentence but keep things readonly at the same time.

upd: In short no, readonly properties are not allowed in any way. Regular constructor and “get” should be used in this case.

Answer 1

This happens because the code you’re using:

Instrument instr = new Instrument { ClassCode = "Hello", Ticker = "World" };

is just syntactic sugar for this:

Instrument instr = new Instrument();
instr.ClassCode = "Hello";
instr.Ticker = "World";

The two samples above are exactly the same, the former is just shorthand for the latter.

What you want to achieve this functionality is to make these values private. Something like this:

class Instrument
{
  private string _classCode;
  private string _ticker;
  public string ClassCode{ get { return _classCode; } }
  public string Ticker{ get { return _ticker; } }
  private ClassCode() {}
  public ClassCode(string classCode, string ticker)
  {
    _classCode = classCode;
    _ticker = ticker;
  }
}

What you have here are:

• Private values which can be set only from within the class, thus they can’t be overridden by someone else later.
• Public read-only properties to read those values.
• A private default constructor so that nobody can instantiate this object without supplying necessary values.
• A public constructor which requires the necessary values.

You’d instantiate it like this:

Instrument instr = new Instrument("Hello", "World");

This means that you wouldn’t be able to use the syntactic sugar (object initializer, I think it’s called) to instantiate the class anymore, you’d have to use the constructor. So this would be a breaking change for the current implementation, but is a simple way to produce the desired functionality.