Setting read-only fields isn't reliable

You can easily see that by running this code on .NET Framework today:

using System;
using System.Reflection;

class Program
{
    private static readonly int s_readonlyValue;

    private static int s_value;

    private static void Main()
    {
        Console.WriteLine(nameof(s_value) + ":");
        for (int i = 0; i < 10; i++)
        {
            typeof(Program).GetField(nameof(s_value), BindingFlags.Static | BindingFlags.NonPublic).SetValue(null, s_value + 1);
            Console.WriteLine(s_value);
        }

        Console.WriteLine();
        Console.WriteLine(nameof(s_readonlyValue) + ":");
        for (int i = 0; i < 10; i++)
        {
            typeof(Program).GetField(nameof(s_readonlyValue), BindingFlags.Static | BindingFlags.NonPublic).SetValue(null, s_readonlyValue + 1);
            Console.WriteLine(s_readonlyValue);
        }
    }
}

This prints:

s_value:
1
2
3
4
5
6
7
8
9
10

s_readonlyValue:
0
0
0
0
0
0
0
0
0
0

because the JIT bakes the value of s_readonlyValue into the call site when it compiles it, and thus isn’t affected by subsequent changes to the field.

terrajobst/issue.md

Setting read-only fields isn't reliable