Question

Does C# allow a variable that can’t be modified? It’s like a const, but instead of having to assign it a value at declaration, the variable does not have any default value, but can only be assigned a value once at runtime (EDIT: and possibly not from constructor). or is this not possible?

Answer 1

You could create your own generic class that provided this functionality, but that might be overkill.

public class SetValueOnce<T>
{
    public bool _set;
    private T _value;

    public SetValueOnce()
    { 
      _value = default(T);
      _set = false;
    }

    public SetValueOnce(T value)
    { 
      _value = value;
      _set = true;
    }

    public T Value
    {
      get
      {
          if(!_set)
             throw new Exception("Value has not been set yet!");
          return _value;
      {
      set
      {
         if(_set)
             throw new Exception("Value already set!");
         _value = value;
         _set = true;
      }
   }
}