I ask because I'm trying to back port something to use with unity which uses C# 2.0. e.g. I have a line like this:
var patternSymbol = Expression.Parameter(typeof (T));
So can I substitute a bit of my own code to make this work? Note: I can change stuff around as I like but the further I get away from the original code the more work I'm likely to run into. Essentially I need to replicate the Expression/Parameter behaviour (from C# 3.0?) in C# 2.0.
(I'm a bit of a C# newbie and finding it difficult to find answers to what are now historical questions like this).
You cannot backport this code to .NET 2.0 because the entire LINQ subsystem is missing. System.Linq.Expressions.Expression class has been introduced as part of LINQ with C# 3.5, which was a big step forward for the .NET framework.
In particular, Expression.Parameter is not useful all by itself. Typically, you would find Expression.Lambda and a Compile calls further down the code, followed by a cast to Func<...>. Imitating these calls would require generating CLR code, which is almost like writing your own compiler. It's rarely worth the effort, though.
You need to see how the old code is used, and build a replacement from scratch. For example, you could replace a compiled expression with an interpreted one, which is considerably easier to build (at the price of lower run-time performance). In any event, you would end up writing an entirely new subsystem, not simply porting the code.
Related
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.
It is not an ideal solution but it is worth considering if you don't want to write everything from the scratch:
If you look on CompileToMethod implementation, you will see that under the hood it uses internal LambdaCompiler class.
If you dig even deeper, you willl see that LambdaCompiler uses System.Reflection.Emit to convert lambdas into MethodInfo.
System.Reflection.Emit is supported by .NET Core.
Taking this into account, my proposition is to try to reuse the LambdaCompiler source code. You can find it here.
The biggest problem with this solution is that:
LambdaCompiler is spread among many files so it may be cumbersome to find what is needed to compile it.
LambdaCompiler may use some API which is not supported by .NET Core at all.
A few additional comments:
If you want to check which API is supported by which platform use .NET API Catalog.
If you want to see differences between .NET standard versions use this site.
Disclaimer: I am author of the library.
I have created Expression Compiler, which has similar API to that of Linq Expressions, with slight changes. https://github.com/yantrajs/yantra/wiki/Expression-Compiler
var a = YExpression.Parameter(typeof(int));
var b = YExpression.Parameter(typeof(int));
var exp = YExpression.Lambda<Func<int,int,int>>("add",
YExpression.Binary(a, YOperator.Add, b),
new YParameterExpression[] { a, b });
var fx = exp.CompileToStaticMethod(methodBuilder);
Assert.AreEqual(1, fx(1, 0));
Assert.AreEqual(3, fx(1, 2));
This library is part of JavaScript compiler we have created. We are actively developing it and we have added features of generators and async/await in JavaScript, so Instead of using Expression Compiler, you can create debuggable JavaScript code and run C# code easily into it.
I ran into the same issue when porting some code to netstandard. My solution was to compile the lambda to a Func using the Compile method, store the Func in a static field that I added to my dynamic type, then in my dynamic method I simply load and call the Func from that static field. This allows me to create the lambda using the LINQ Expression APIs instead of reflection emit (which would have been painful), but still have my dynamic type implement an interface (which was another requirement for my scenario).
Feels like a bit of a hack, but it works, and is probably easier than trying to recreate the CompileToMethod functionality via LambdaCompiler.
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.
Does anyone know if there is a way to evaluate c# code at runtime.
eg. I would like to allow a user to enter DateTime.Now.AddDays(1), or something similar, as a string and then evaluate the string to get the result.
I woder if it is possible to access the emmediate windows functionality, since it seems that is evaluates every line entered dynamically.
I have found that VB has an undocumented EbExecuteLine() API function from the VBA*.dll and wonder if there is something equivalent for c#.
I have also found a custom tool https://github.com/DavidWynne/CSharpEval (it used to be at kamimucode.com but the author has moved it to GitHub) that seems to do it, but I would prefer something that comes as part of .NET
Thanks
Mono has the interactive command line (csharp.exe)
You can look at it's source code to see exactly how it does it's magic:
https://github.com/mono/mono/raw/master/mcs/tools/csharp/repl.cs
As you've probably already seen, there is no built-in method for evaluating C# code at runtime. This is the primary reason that the custom tool you mentioned exists.
I also have a C# eval program that allows for evaluating C# code. It provides for evaluating C# code at runtime and supports many C# statements. In fact, this code is usable within any .NET project, however, it is limited to using C# syntax. Have a look at my website, http://csharp-eval.com, for additional details.
Microsoft's C# compiler don't have Compiler-as-a-Service yet (Should come with C# 5.0).
You can either use Mono's REPL, or write your own service using CodeDOM
Its not fast but you can compile the code on the fly, see my previous question,
Once you have the assembly and you know the type name you can construct an instance of your compiled class using reflection and execute your method..
The O2 Platform's C# REPL Script Environment use the Fluent# APIs which have a real powerful reflection API that allows you do execute code snippets.
For example:
"return DateTime.Now.ToLongTimeString();".executeCodeSnippet();
will return
5:01:22 AM
note that the "...".executeCodeSnippet(); can actually execute any valid C# code snippet (so it is quite powerful).
If you want to control what your users can execute, I could use AST trees to limite the C# features that they have access to.
Also take a look at the Microsoft's Roslyn, which is VERY powerful as you can see on Multiple Roslyn based tools (all running Stand-Alone outside VisualStudio)
I'm making a Genetic Program, but I'm hitting a limitation with C# where I want to present new functions to the algorithm but I can't do it without recompiling the program. In essence I want the user of the program to provide the allowed functions and the GP will automatically use them. It would be great if the user is required to know as little about programming as possible.
I want to plug in the new functions without compiling them into the program. In Python this is easy, since it's all interpreted, but I have no clue how to do it with C#. Does anybody know how to achieve this in C#? Are there any libraries, techniques, etc?
It depends on how you want the user of the program to "provide the allowed functions."
If the user is choosing functions that you've already implemented, you can pass these around as delegates or expression trees.
If the user is going to write their own methods in C# or another .NET language, and compile them into an assembly, you can load them using Reflection.
If you want the user to be able to type C# source code into your program, you can compile that using CodeDom, then call the resulting assembly using Reflection.
If you want to provide a custom expression language for the user, e.g. a simple mathematical language, then (assuming you can parse the language) you can use Reflection.Emit to generate a dynamic assembly and call that using -- you guessed it -- Reflection. Or you can construct an expression tree from the user code and compile that using LINQ -- depends on how much flexibility you need. (And if you can afford to wait, expression trees in .NET 4.0 remove many of the limitations that were in 3.5, so you may be able to avoid Reflection.Emit altogether.)
If you are happy for the user to enter expressions using Python, Ruby or another DLR language, you can host the Dynamic Language Runtime, which will interpret the user's code for you.
Hosting the DLR (and IronPython or IronRuby) could be a good choice here because you get a well tested environment and all the optimisations the DLR provides. Here's a how-to using IronPython.
Added in response to your performance question: The DLR is reasonably smart about optimisation. It doesn't blindly re-interpret the source code every time: once it has transformed the source code (or, specifically, a given function or class) to MSIL, it will keep reusing that compiled representation until the source code changes (e.g. the function is redefined). So if the user keeps using the same function but over different data sets, then as long as you can keep the same ScriptScope around, you should get decent perf; ditto if your concern is just that you're going to run the same function zillions of times during the genetic algorithm. Hosting the DLR is pretty easy to do, so it shouldn't be hard to do a proof of concept and measure to see if it's up to your needs.
You can try to create and manipulate Expression Trees. Use Linq to evaluate expression trees.
You can also use CodeDom to compile and run a function.
For sure you can google to see some examples that might fit your needs.
It seems that this article "How to dynamically compile C# code" and this article "Dynamically executing code in .Net" could help you.
You have access to the Compiler from within code, you can then create instances of the compiled code and use them without restarting the application. There are examples of it around
Here
and
Here
The second one is a javascript evaluator but could be adapted easily enough.
You can take a look at System.Reflection.Emit to generate code at the IL level.
Or generate C#, compile into a library and load that dynamically. Not nearly as flexible.
It is in fact very easy to generate IL. See this tutorial: http://www.meta-alternative.net/calc.pdf
I need to parse a simple statement (essentially a chain of function calls on some object) represented as a string variable into a CodeDom object (probably a subclass of CodeStatement). I would also like to provide some default imports of namespaces to be able to use less verbose statements.
I have looked around SO and the Internet to find some suggestions but I'm quite confused about what is and isn't possible and what is the simplest way to do it. For example this question seems to be almost what I want, unfortunately I can't use the solution as the CodeSnippetStatement seems not to be supported by the execution engine that I use (the WF rules engine).
Any suggestions that could help me / point me into the right direction ?
There is no library or function to parse C# code into CodeDOM objects as part of the standard .NET libraries. The CodeDOM libraries have some methods that seem to be designed for this, but none of them are actually implemented. As far as I know, there is some implementation available in Visual Studio (used e.g. by designers), but that is only internal.
CodeSnippetStatement is a CodeDOM node that allows you to place any string into the generated code. If you want to create CodeDOM tree just to generate C# source code, than this is usually fine (the source code generator just prints the string to the output). If the WF engine needs to understand the code in your string (and not just generate source code and compile it), than CodeSnippetStatement won't work.
However, there are 3rd party tools that can be used for parsing C# source code. In one project I worked on, we used NRefactory library (which is used in SharpDevelop) and it worked quite well. It gives you some tree (AST) representing the parsed code and I'm afraid you'll need to convert this to the corresponding CodeDOM tree yourself.
I have found a library implementation here that seems to cover pretty much everything I need for my purposes. I don't know if it's robust enough to be used in business scenarios, but for my unit tests it's pretty much all I can ask for.
I am writing a fairly simple code gen tool, and I need the ability to convert MSIL (or MethodInfo) objects to their C# source. I realize Reflector does a great job of this, but it has the obnoxious "feature" of being UI only.
I know I could just generate the C# strings directly, using string.Format to insert the variable portions, but I'd really prefer to be able to generate methods programatically (e.g. a delegate or MethodInfo object), then pass those methods to a writer which would convert them to C#.
It seems a little silly that the System libraries make it so easy to go from a C# source code string to a compiled (and executable) method at runtime, but impossible to go from an object to source code--even for simple things.
Any ideas?
This add-in for Reflector lets you output to a file, and it is possible to run Reflector from the command line. It's probably simpler to get that to do what you want than to roll your own decompiler.
Anakrino is another decompiler with a command line option, but it hasn't been updated since .NET 1.1. It's open source, though, so you might be able to base your solution on it.
The code generators which I wrote as part of our application use String.Format, and although I am not entirely happy with String.Format (Lisp macros beat it any time of the day) it does the job all right. The C# compiler is going to re-check all your generated methods anyway, so you gain nothing by round-tripping through Reflection.Emit and the (still unwritten) MSIL-to-C# decompiler.
PS: why not use CodeDOM if you want to use something heavyweight?