Why can't I initialize an Init property directly/without the use of an Object Initializer?

Question

Hello,

We can initialize the Init property with Object Initializer. In fact, an Object initializer is equivalent to the variable/property initializer.

If the compiler translates an Object initializer to a conventional variable initialization, Why can't I initialize an Init property directly/without the use of an Object Initializer?

namespace ConsoleApp1
{
     internal class Program
     {
          static void Main(string[] args)
          {
               My m = new()
               {
                    MyProperty = 10
               };
               My m1 = new();
               // m1.MyProperty = 10; //ERROR
               Console.WriteLine(m1.MyProperty);
          }
     }
     class My
     {
          public int MyProperty { get; init; }
          public My()
          {
          }
     }
}

Answer 1

Why are you decompiling with most oldest version intentionally?

Object-Initializers cannot be expressed in C#1 because of the description method introduced in C# version 3.

It stands to reason that if you decompile with older version, it will not be able to interpret the new functionality.
Compilers that support C#9 can now add custom modifiers to property setters to enable new access restrictions.

//public int MyProperty { get; set; }
.method public hidebysig specialname instance void set_MyProperty (int32 'value') cil managed 

//public int MyProperty { get; internal set; }
.method assembly hidebysig specialname instance void set_MyProperty (int32 'value') cil managed 

//public int MyProperty { get; init; }
.method public hidebysig specialname instance void modreq([System.Runtime]System.Runtime.CompilerServices.IsExternalInit) set_MyProperty (int32 'value') cil managed 

//public int MyProperty { get; internal init; }
.method assembly hidebysig specialname instance void modreq([System.Runtime]System.Runtime.CompilerServices.IsExternalInit) set_MyProperty (int32 'value') cil managed 

modreq in IL is Custom modifier for member access like as public or private.

If you use compiler that is supported only older versions, it will not be able to resolve this modifier and therefore will not compile.
Similarly, ILSpy's C# 1.0 decompiler is not able to decompile this modreq as an init.

For a more detailed understanding you need to study the IL language.

Answer 2

The init operator is a compiler feature (syntax sugar), not a .net runtime feature. The compiler uses the property to set the value, but disallows code from doing it. The il decompiler is not smart enough to produce compilable code.