C# Getting a previously defined method builder from the type builder

Question

Consider the following C# code:

var methodBuilder1 = typeBuilder.DefineMethod("GetMedalIds", MethodAttributes.Public | MethodAttributes.HideBySig, CallingConventions.HasThis, typeof(int[]), null);

var methodBuilder2 = typeBuilder.DefineMethod("GetMedalIds", MethodAttributes.Public | MethodAttributes.HideBySig, CallingConventions.HasThis, typeof(int[]), null);

First, note that the arguments into DefineMethod are identical (and arbitrary), and typeBuilder is the same instance in both cases. With this in mind, I have discovered the methodBuilder1 and methodBuilder2 both point to the same instance (at least methodBuiilder1 == methodBuilder2 is always true), leading me to assume that if the method builder hasn't already been defined, type builder defines it, otherwise it returns the already defined method builder.

My question is this: The comments on DefineMethod(...) says nothing about the above, so are my assumptions GUARANTEED to always be true as far as the C# specification is concerned, or is it an implementation detail that is subject to change? .

BurnsBA · Accepted Answer · 2022-10-01 14:25:59Z

1

Assumptions in the question are incorrect. The instances are logically equivalent (== returns true), but point to separate instances. You can test this with Object.ReferenceEquals(...).

Use this answer for dotnet core 3.1:

using System;
using System.Reflection;
using System.Reflection.Emit;

namespace MethodBuilderDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            AssemblyName asmName = new AssemblyName("DemoMethodBuilder1");
            AssemblyBuilder demoAssembly = AssemblyBuilder.DefineDynamicAssembly(new AssemblyName(Guid.NewGuid().ToString()), AssemblyBuilderAccess.Run);
            ModuleBuilder demoModule = demoAssembly.DefineDynamicModule(asmName.Name);

            TypeBuilder demoType = demoModule.DefineType("DemoType",TypeAttributes.Public | TypeAttributes.Abstract);

            var methodBuilder1 = demoType.DefineMethod("GetMedalIds", MethodAttributes.Public | MethodAttributes.HideBySig, CallingConventions.HasThis, typeof(int[]), null);
            var methodBuilder2 = demoType.DefineMethod("GetMedalIds", MethodAttributes.Public | MethodAttributes.HideBySig, CallingConventions.HasThis, typeof(int[]), null);

            Console.WriteLine($"==: {methodBuilder1 == methodBuilder2}");
            Console.WriteLine($"ref equals: {Object.ReferenceEquals(methodBuilder1, methodBuilder2)}");
        }
    }
}

gives

==: True
ref equals: False

answered Oct 1, 2022 at 14:25

BurnsBA

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1 Comment

Dantte Over a year ago

Thanks @BurnsBA. My follow up question will be: does the equivalence guarantee that changes/modifications to one instance will reflect in the other? Ps: I'll test this out and possibly post my finding here too, if no one has responded by then.

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