Alternatives of CompileToMethod in .Net Standard

Question

I'm now porting some library that uses expressions to .Net Core application and encountered a problem that all my logic is based on LambdaExpression.CompileToMethod which is simply missing in. Here is sample code:

public static MethodInfo CompileToInstanceMethod(this LambdaExpression expression, TypeBuilder tb, string methodName, MethodAttributes attributes)
{
    ...

    var method = tb.DefineMethod($"<{proxy.Name}>__StaticProxy", MethodAttributes.Private | MethodAttributes.Static, proxy.ReturnType, paramTypes);
    expression.CompileToMethod(method);

    ...
}

Is it possible to rewrite it somehow to make it possible to generate methods using Expressions? I already can do it with Emit but it's quite complex and i'd like to avoid it in favor of high-level Expressions.

I tried to use var method = expression.Compile().GetMethodInfo(); but in this case I get an error:

System.InvalidOperationException : Unable to import a global method or field from a different module.

I know that I can emit IL manually, but I need exactly convert Expression -> to MethodInfo binded to specific TypeBuilder instead of building myself DynamicMethod on it.

Answer 1

Attempting to get LambdaCompiler working on .NET Core

Building on Michal Komorowski's answer, I decided to give porting LambdaCompiler to .NET Core a try. You can find my effort here (GitHub link). The fact that the class is spread over multiple files is honestly one of the smallest problems here. A much bigger problem is that it relies on internal parts in the .NET Core codebase.

Quoting myself from the GitHub repo above:

Unfortunately, it is non-trivial because of (at least) the following issues:

• AppDomain.CurrentDomain.DefineDynamicAssembly is unavailable in .NET Core - AssemblyBuilder.DefineDynamicAssembly replaces is. This SO answer describes how it can be used.

• Assembly.DefineVersionInfoResource is unavailable.

• Reliance on internal methods and properties, for example BlockExpression.ExpressionCount, BlockExpression.GetExpression, BinaryExpression.IsLiftedLogical etc.

For the reasons given above, an attempt to make this work as a standalone package is quite unfruitful in nature. The only realistic way to get this working would be to include it in .NET Core proper.

This, however, is problematic for other reasons. I believe the licensing is one of the stumbling stones here. Some of this code was probably written as part of the DLR effort, which it itself Apache-licensed. As soon as you have contributions from 3rd party contributors in the code base, relicensing it (to MIT, like the rest of the .NET Core codebase) becomes more or less impossible.

Other options

I think your best bet at the moment, depending on the use case, is one of these two:

• Use the DLR (Dynamic Language Runtime), available from NuGet (Apache 2.0-licensed). This is the runtime that empowers IronPython, which is to the best of my knowledge the only actively maintained DLR-powered language out there. (Both IronRuby and IronJS seems to be effectively abandoned.) The DLR lets you define lambda expressions using Microsoft.Scripting.Ast.LambdaBuilder; this doesn't seem to be directly used by IronPython though. There is also the Microsoft.Scripting.Interpreter.LightCompiler class which seems to be quite interesting.

  The DLR unfortunately seems to be quite poorly documented. I think there is a wiki being referred to by the CodePlex site, but it's offline (can probably be accessed by downloading the archive on CodePlex though).

• Use Roslyn to compile the (dynamic) code for you. This probably has a bit of a learning curve as well; I am myself not very familiar with it yet unfortunately.

  This seems to have quite a lot of curated links, tutorials etc: https://github.com/ironcev/awesome-roslyn. I would recommend this as a starting point. If you're specifically interested in building methods dynamically, these also seem worth reading:

  • https://gunnarpeipman.com/using-roslyn-to-build-object-to-object-mapper/
  • http://www.tugberkugurlu.com/archive/compiling-c-sharp-code-into-memory-and-executing-it-with-roslyn

  Here are some other general Roslyn reading links. Most of these links are however focused on analyzing C# code here (which is one of the use cases for Roslyn), but Roslyn can be used to generate IL code (i.e. "compile") C# code as well.

  • The .NET Compiler Platform SDK: https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/
  • Get started with syntax analysis: https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/get-started/syntax-analysis
  • Tutorial: Write your first analyzer and code fix: https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/tutorials/how-to-write-csharp-analyzer-code-fix

There is also the third option, which is probably uninteresting for most of us:

• Use System.Reflection.Emit directly, to generate the IL instructions. This is the approach used by e.g. the F# compiler.