Why does an overridden get-only property stay null when set in base class constructor?

Question

I tried the following example:

public class TestBase {     public virtual string ReadOnly { get; }      public TestBase()     {         ReadOnly = "from base";     } }  class Test : TestBase {     public override string ReadOnly { get; }     public Test()     {         // nothing here     } } 

When I create an instance of Test, I see that ReadOnly stays null. But why? I really do not get the hang of it, could somebody please explain to me why this happens? At least I would expect an error, that a read-only property cannot be set outside of the owning class.

Answer 1

The compiler treats this as below; basically, the code in the constructor writes to the original backing field, in TestBase. It seems that yours is not a supported scenario, but... I do wonder whether the language team have considered this case.

BTW: if you ever want to see what the compiler does with code: sharplab.io

public class TestBase {     [CompilerGenerated]     private readonly string <ReadOnly>k__BackingField; // note: not legal in "real" C#      public virtual string ReadOnly     {         [CompilerGenerated]         get         {             return <ReadOnly>k__BackingField; // the one in TestBase         }     }      public TestBase()     {         <ReadOnly>k__BackingField = "from base";     } } internal class Test : TestBase {     [CompilerGenerated]     private readonly string <ReadOnly>k__BackingField;      public override string ReadOnly     {         [CompilerGenerated]         get         {             return <ReadOnly>k__BackingField; // the one in Test         }     } }