not init property

[Terry1511512]

I would like to see a "not init" property which forbids a property being used during initialisation.
Often a property is only usable after initialisation. If used in initialisation it then becomes dependent on initialisation order.

public class Idea
{
public string Value { get; set; }
public string SomeValue { get; set; } // Depends upon Value being initialised
}

var Idea = new Idea // Works
{
Value = "XXXX",
SomeValue = "YYYY"
};

var Idea = new Idea // Won't Work
{
SomeValue = "YYYY", // Value not initialised
Value = "XXXX"
};

A "not init" property that forbids the property being used in initialisation would stop this happening.

public class Idea
{
public string Value { get; set; }
public string SomeValue { get; not init; } // Depends upon Value being initialised
}

[theunrepentantgeek]

The usual response from the LDM when someone wants the language to prevent certain scenarios is to suggest writing an analyzer that implements your specific needs.

[Unknown6656]

Why not use a instance method as "setter" for that?
That way, all calls are guaranteed to be executed after the initialization performed by the constructor.

public class Idea
{
     private string _some_value;

     public string Value { get; set; }
     public string SomeValue => _some_value; // getter always accessible


     public Idea() => _some_value = "Hello World!";

     public void SetSomeValue(string value)
     {
          // .... some logic
          _some_value = value;
     }
}

However, If you like the assignment syntax or like to use some operators, I'd advise you to use ref returns:

public class Idea
{
     private string _some_value;

     public string Value { get; set; }

     public Idea() => _some_value = "Hello World!";

     public ref string SomeValue() => ref _some_value;
}

Which can be used thus:

Idea i = new Idea { Value = "value" };

i.SomeValue() = "42";
string s = i.SomeValue();

[Terry1511512]

Of course I can always use methods but that's changing the usage away from a property syntax. I still want to use it as a normal property, just not in initialisation.

[Joe4evr]

Then writing an analyzer that ships in your library is basically your only option.