I'm writing a console tool to generate some C# code for objects in a class library. The best/easiest way I can actual generate the code is to use reflection after the library has been built. It works great, but this seems like a haphazard approch at best. Since the generated code will be compiled with the library, after making a change I'll need to build the solution twice to get the final result, etc. Some of these issues could be mitigated with a build script, but it still feels like a bit too much of a hack to me.
My question is, are there any high-level best practices for this sort of thing?
Its pretty unclear what you are doing, but what does seem clear is that you have some base line code, and based on some its properties, you want to generate more code.
So the key issue here are, given the base line code, how do you extract interesting properties, and how do you generate code from those properties?
Reflection is a way to extract properties of code running (well, at least loaded) into the same execution enviroment as the reflection user code. The problem with reflection is it only provides a very limited set of properties, typically lists of classes, methods, or perhaps names of arguments. IF all the code generation you want to do can be done with just that, well, then reflection seems just fine. But if you want more detailed properties about the code, reflection won't cut it.
In fact, the only artifact from which truly arbitrary code properties can be extracted is the the source code as a character string (how else could you answer, is the number of characters between the add operator and T in middle of the variable name is a prime number?). As a practical matter, properties you can get from character strings are generally not very helpful (see the example I just gave :).
The compiler guys have spent the last 60 years figuring out how to extract interesting program properties and you'd be a complete idiot to ignore what they've learned in that half century.
They have settled on a number of relatively standard "compiler data structures": abstract syntax trees (ASTs), symbol tables (STs), control flow graphs (CFGs), data flow facts (DFFs), program triples, ponter analyses, etc.
If you want to analyze or generate code, your best bet is to process it first into such standard compiler data structures and then do the job. If you have ASTs, you can answer all kinds of question about what operators and operands are used. If you have STs, you can answer questions about where-defined, where-visible and what-type. If you have CFGs, you can answer questions about "this-before-that", "what conditions does statement X depend upon". If you have DFFs, you can determine which assignments affect the actions at a point in the code. Reflection will never provide this IMHO, because it will always be limited to what the runtime system developers are willing to keep around when running a program. (Maybe someday they'll keep all the compiler data structures around, but then it won't be reflection; it will just finally be compiler support).
Now, after you have determined the properties of interest, what do you do for code generation? Here the compiler guys have been so focused on generation of machine code that they don't offer standard answers. The guys that do are the program transformation community (http://en.wikipedia.org/wiki/Program_transformation). Here the idea is to keep at least one representation of your program as ASTs, and to provide special support for matching source code syntax (by constructing pattern-match ASTs from the code fragments of interest), and provide "rewrite" rules that say in effect, "when you see this pattern, then replace it by that pattern under this condition".
By connecting the condition to various property-extracting mechanisms from the compiler guys, you get relatively easy way to say what you want backed up by that 50 years of experience. Such program transformation systems have the ability to read in source code,
carry out analysis and transformations, and generally to regenerate code after transformation.
For your code generation task, you'd read in the base line code into ASTs, apply analyses to determine properties of interesting, use transformations to generate new ASTs, and then spit out the answer.
For such a system to be useful, it also has to be able to parse and prettyprint a wide variety of source code langauges, so that folks other than C# lovers can also have the benefits of code analysis and generation.
These ideas are all reified in the
DMS Software Reengineering Toolkit. DMS handles C, C++, C#, Java, COBOL, JavaScript, PHP, Verilog, ... and a lot of other langauges.
(I'm the architect of DMS, so I have a rather biased view. YMMV).
Have you considered using T4 templates for performing the code generation? It looks like it's getting much more publicity and attention now and more support in VS2010.
This tutorial seems database centric but it may give you some pointers: http://www.olegsych.com/2008/09/t4-tutorial-creatating-your-first-code-generator/ in addition there was a recent Hanselminutes on T4 here: http://www.hanselminutes.com/default.aspx?showID=170.
Edit: Another great place is the T4 tag here on StackOverflow: https://stackoverflow.com/questions/tagged/t4
EDIT: (By asker, new developments)
As of VS2012, T4 now supports reflection over an active project in a single step. This means you can make a change to your code, and the compiled output of the T4 template will reflect the newest version, without requiring you to perform a second reflect/build step. With this capability, I'm marking this as the accepted answer.
You may wish to use CodeDom, so that you only have to build once.
First, I would read this CodeProject article to make sure there are not language-specific features you'd be unable to support without using Reflection.
From what I understand, you could use something like Common Compiler Infrastructure (http://ccimetadata.codeplex.com/) to programatically analyze your existing c# source.
This looks pretty involved to me though, and CCI apparently only has full support for C# language spec 2. A better strategy may be to streamline your existing method instead.
I'm not sure of the best way to do this, but you could do this
As a post-build step on your base dll, run the code generator
As another post-build step, run csc or msbuild to build the generated dll
Other things which depend on the generated dll will also need to depend on the base dll, so the build order remains correct
Related
Background
Part of the project I'm working on requires me to analyze Q# source code and perform specific actions when certain syntax elements are encountered. For example, say I'd like to count how many different gate types are used throughout the program. Now, this could be implemented by walking the Abstract Syntax Tree of the program and performing actions based on the current syntax node.
What I've tried
I've started by analyzing the qsharp-compiler repository, however, the inner workings of the compiler lack online documentation and browsing all the C# and F# sources can be really tedious.
Of course, I could write my own parser for the language, but that would probably be an overkill for the task at hand. There has to be a way to extract the AST from inside of the compiler.
The question
Is there a way to compile Q# source code using the Q# compiler programmatically (from C# or F#), and extract the internal AST?
Yes, it is perfectly possible to compile Q# source code programmatically. This is particularly useful if you want to repeatedly update a compilation - you can add/remove/edit (parts of) the sources and references in memory, and query all kinds of useful information about the current state of the compilation that e.g. an IDE cares about (like e.g. which symbols are defined at a particular location in a certain file).
However, if you just want to process the AST for a Q# compilation, then there is a much easier way! The Q# compiler has an extensibility mechanism that I believe fits your need perfectly.
This blog post gives a brief overview over the feature.
There is also an example for an extension on the compiler repo. This readme (and possibly this one) may also come in handy. I believe this answers half of your question, namely how to easily get access to the built AST.
The other half of the question according to my interpretation is how to conveniently analyze or transform the AST. For that there is also a mechanism provided; the syntax tree transformation framework. That framework consists of a couple of classes that define the walk/transformation for different kinds of nodes, as well as a wrapping class that plugs it all together.
Rather than starting by looking at the definition of the transformations, it is probably more intuitive to just look at some examples that use it. An example that is pretty close to what you want to do can be found here. The implemented transformation adds a comment to each callable listing all identifiers used within the callable. It is invoked as as part of a compilation step (see here) that is defined in the example I already linked above.
There are a couple of other good examples for simple transformations that are a bit farther from what you want to do, but should give you an idea how the whole setup works if you are interested: this one allows to attach attributes to callables, and this one is used to inline conjugations (pattern of the form U*VU).
Last but not least, the Gitter for the Q# community can possibly also be a good resource to engage as you work.
I would like to build an application framework that is mainly interpreted.
Say that the source code would be stored in the database that could be edited by the users and always the latest version would be executed.
Can anyone give me some ideas how does one implement sth like this !
cheers,
gabor
In .Net, you can use reflection and CodeDOM to compile code on the fly. But neither approach is really very simple or practical. Mono has some ability to interpret c# on the fly as well, but I haven't looked closely at it yet.
Another alternative is to go with an interpreted .Net language like Boo or IronPython as the language for your database code.
Either way, make sure you think long and hard about the security of your platform. Allowing users to execute arbitrary code is always an exercise fraught with peril. It's often too tempting to look for a simple eval() method, and even if one exists, that is not good enough for this kind of scenario.
Try Mono ( http://www.monoproject.org ). It supports many scripting languages including JavaScript.
If you don't want to use any scripting you can use CodeDOM or Reflection (see Reflection.Emit).
Here are really useful links on the topic :
Dynamically executing code in .Net (Here you can find a tool which can be very helpul)
Late Binding and On-the-Fly Code
Generation Using Reflection in C#
Dynamic Source Code Generation and
Compilation
Usually the Program uses a scripting language for the scriptable parts, i.e. Lua or Javascript.
To answer your technical question: You don't want to write your own language and interpreter. That's too much work for you to do. So pick some other language, say Python or Lua, and look for the documentation that lets your C program hand it blocks of code to execute. Of course, the script needs to be able to do something, so you'll need to find how to expose your program's objects to the script. Also, what will happen if a client is running the program when you update its source code in the database? Should the client restart? Are you going to store the entire program as a single row in this database, or did you want to store individual functions? That affects how you structure your updates.
To address other issues with your question: Why do you want to do this? Making "interpreted language" part of your design spec for a system is not often a good sign. Is the real requirement something like this: "I update the program often and I want users to always have the latest copy?" If so, there are other, better ways to go about this (just give us your actual scenario and requirements).
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 currently developing an application where you can create "programs" with it without writing source code, just click&play if you like.
Now the question is how do I generate an executable program from my data model. There are many possibilities but I am not sure which one is the best for me. I need to generate assemblies with classes and namespace and everything which can be part of the application.
CodeDOM class: I heard of lots of limitations and bugs of this class. I need to create attributes on method parameters and return values. Is this supported?
Create C# source code programmatically and then call CompileAssemblyFromFile on it: This would work since I can generate any code I want and C# supports most CLR features. But wouldn't this be slow?
Use the reflection ILGenerator class: I think with this I can generate every possible .NET code. But I think this is much more complicated and error prone than the other approaches?
Are there other possible solutions?
EDIT:
The tool is general for developing applications, it is not restricted to a specific domain. I don't know if it can be considered a visual programming language. The user can create classes, methods, method calls, all kinds of expressions. It won't be very limitating because you should be able to do most things which are allowed in real programming languages.
At the moment lots of things must still be written by the user as text, but the goal at the end is, that nearly everything can be clicked together.
You my find it is rewarding to look at the Dynamic Language Runtime which is more or less designed for creating high-level languages based on .NET.
It's perhaps also worth looking at some of the previous Stack Overflow threads on Domain Specific Languages which contain some useful links to tools for working with DSLs, which sounds a little like what you are planning although I'm still not absolutely clear from the question what exactly your aim is.
Most things "click and play" should be simple enough just to stick some pre-defined building-block objects together (probably using interfaces on the boundaries). Meaning: you might not need to do dynamic code generation - just "fake it". For example, using property-bag objects (like DataTable etc, although that isn't my first choice) for values, etc.
Another option for dynamic evaluation is the Expression class; especially in .NET 4.0, this is hugely versatile, and allows compilation to a delegate.
Do the C# source generation and don't care about speed until it matters. The C# compiler is quite quick.
When I wrote a dynamic code generator, I relied heavily on System.Reflection.Emit.
Basically, you programatically create dynamic assemblies and add new types to them. These types are constructed using the Emit constructs (properties, events, fields, etc..). When it comes to implementing methods, you'll have to use an ILGenerator to pump out MSIL op-codes into your method. That sounds super scary, but you can use a couple of tools to help:
A pre-built sample implementation
ILDasm to inspect the op-codes of the sample implementation.
It depends on your requirements, CodeDOM would certainly be the best fit for a "program" stored it in a "data model".
However its unlikely that using option 2 will be in any way measurably slower in comparision with any other approach.
I would echo others in that 1) the compiler is quick, and 2) "Click and Play" things should be simple enough so that no single widget added to a pile of widgets can make it an illegal pile.
Good luck. I'm skeptical that you can achieve point (2) for anything but really toy-level programs.
Since yesterday, I am analyzing one of our project with Ndepend (free for most of its features) and more I am using it, and more I have doubt about the real value of this type of software (code-analysis software).
Let me explain, The system build a report about the health of the system and class by Rank every metric. I thought it would be a good starting point to do modifications but most of the top result are here because they have over 100 lines inside the class (we have big headers and we do use VS comments styles) so it's not a big deal... than the number of Afferent Coupling level (CA) is always too high and this is almost very true for Interface that we used a lot... so at this moment I do not see something wrong but NDepend seem to do not like it (if you have suggestion to improve that tell me because I do not see the need for). It's the samething for the metric called "NOC" for Number of children that most of my Interface are too high...
For the moment, the only very useful metric is the Cyclomatic Complexity...
My question is : Do you find is worth it to analyse code with Automatic Code Analyser like NDepend? If yes, how do you filter all information that I have mentionned that doesn't really show the real health of the system?
Actually metrics are just one feature of NDepend, did you try to use VisualNDepend that lets you analyze your project much more in depth than the report? By reading your comment, I am almost sure you didn't play with NDepend UI (standalone or integrated in Visual Studio) which is the best way to filter data about your code base.
I am one of the developers of NDepend and we use it a lot to analyze our own code. Basically we write our own quality rules with Code Rules over LINQ Queries (CQLinq). These rules automatically make sure that we don't have regression on our design. Here you'll find the list of around 200 default code rules.
Here are some unique features of NDepend and not related to code metrics:
Write CQLinq rules to make sure we don't have architectural flaws, such as dependency cycles between our components, UI using directly the DB or DB entangled with the business objects.
Make sure we don't have problem with code coverage by tests (like we make sure with a CQLinq rule that if a class is supposed to be 100% covered, it will remain 100% covered in the future)
Enforce side-effects-free code (immutable class/pure methods)
Use the ability to compare 2 analysis to code review changes since the last release, before doing a new release. More specifically, I enjoy using NDepend to know which method has been added and refactored since the last release, and is not 100% covered by tests.
Having an optimal encapsulation for all our members and types (like knowing which internal methods can be declared as private). This is also related to dead-code detection that NDepend also supports.
For a complete list of features if NDepend, see here.
I don't necessarily see NDepend results as "good" or "bad" in software engineering, there's always a good reason why an application is designed the way it is. I see it as a report that can probably help me point out issues with my design, but I have the final word when it comes to deciding if a method needs to be refactored or if it's good the way I designed it. In general, don't get too caught up trying to answer if it's worth it or not. It definitely is, instead I would suggest you carefully review the results. This will help you view your design from another perspective and there may be occasions where you decide the way you designed it is the best to achieve your applications goals.