assign value of readonly variable in private method called only by constructors

Question

C# compiler gave me the following error

CS0191: A readonly field cannot be assigned to (except in a constructor or a variable initializer)

Do I have to move the code (in my private function) into the constructor? That sounds awkward.

Note that the private method was intended only to be called by the constructor. I expect that there is some sort of attribute that I can use to mark the method corresponding.

Answer 1

Despite what the other posts are saying, there is actually a (somewhat unusual) way to do this and actually assign the value in a method:

public class Foo {     private readonly string _field;      public Foo(string field)     {         Init(out _field, field);     }      private static void Init(out string assignTo, string value)     {         assignTo = value;     } } 

Example derived from here.

Alternatively, you can also return the value from a private method and assign it in the constructor as follows:

class Foo {     private readonly string _field;      public Foo()     {         _field = GetField();     }      private string GetField()     {         return "MyFieldInitialization";     } } 

Answer 2

Readonly field can only be assigned by the constructor. What you can do is to initialize the field with a method:

class Foo {     private readonly Bar _bar = InitializeBar();      private Bar InitializeBar()     {         // Add whatever logic you need to obtain a Foo instance.         return new Bar();     } }