C# dynamic code evaluation, Eval, REPL

Question

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

Answer 1

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

Answer 2

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.

Answer 3

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)

Answer 4

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

Answer 5

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..