Related
I hear a lot about boost here and I am beginning to think it could help a lot with my software development. More so in concurrency and memory management in my particular case as we have had a lot of bugs in this area.
What are the key language features I need to polish up on to effectively benefit from using boost and to shorten the learning curve? I have seen that function objects are commonly used so I would probably need to polish up on that.
Additionally, are there any tutorials and 101 resources I can quickly look at to just get a feel and understanding on using boost.
I realise there is a lot boost offers and I have to pick the right tools for the right job but any leads will help.
Related
How to learn boost (no longer valid; HTTP return status 404)
Boost has an unimaginable number of libraries.
Easy ones to get started on are
noncopyable
array
circular_buffer
foreach
operators (one of my personal favorites)
smart_ptr
date_time
More advanced ones include
lambda
bind
iostreams
serialization
threads
Getting used to boost takes time, but I assure you it will make your life much better. Plus, looking at how the boost libraries are coded will help you get better at c++ coding, especially templates.
You mentioned what should you look up before trying boost. I agree that function objects are a great thing to research. Also, make sure to look up about template programming. A common problem to make sure you know is when to use the typename qualifier for dependent types. For the most part, however, the libraries are very well documented, with examples and reference materials.
Learning boost is discussed here. As for language features that are useful? All of them. C++ is a dangerous language to use if you don't know enough of it. RAII, functors/function objects and templates probably cover the most important aspects. Boost is designed similarly to the STL, so knowing your standard library is essential. Boost itself uses a lot of template metaprogramming, but as a library user, you won't often need that (unless you start playing with Boost.MPL)
Bugs related to memory management are a good indicator that it's C++, rather than Boost you need to brush up on. The techniques for handling memory safely are well known, and not specific to Boost. (With the obvious exception of Boost's smart pointers). RAII is probably the most important concept to understand to deal with this kind of issues.
What are the key language features I need to polish up on to effectively benefit from using boost and to shorten the learning curve?
Templates
Functors
Exceptions
STL
Iterators
Algorithms
Containers
... among others.
are there any tutorials and 101 resources I can quickly look at to just get a feel and understanding on using boost.
Boost is well documented. Start here.
There are too many libraries to get lost. I'd say start with something simple, maybe smart pointers or Boost.Test (Unit Test framework) -- which will quickly help you get started. Also, try to think of a problem you cannot solve with the STL easily. Then look up Boost documentation or post here.
If you are comfortable with functional programming look at MPL/Lambda libraries.
The first ting IMO are smart pointers. Integration into new code is simple, and usually not a problem for existing code. They make memory management easy, and work for many other ressources, too.
C++ gives you the power to manage your own memory, smart pointers let you (mostly) wing it when you don't need to.
The second would be - as you mentioned - function objects, they close a big gap within C++ that is traditionally solved through inheritance, which is to strong of a coupling in many cases.
I have only little experience with boost outside these two, but most of the remainder is fairly "situational" - you may or may not need it. Get an overview over the libraries, and see what you need.
boost::any and boost::variant are good of you need a variant data type, with two different approaches.
boost::regex if you need some text parsing.
boost::thread and boost::filesystem help you write portable code. If you already have good platform specific libraries, you might not need them - but they are better than API or C++ level in any case.
Maybe you like my introduction to boost smart pointers, and a rather unorthodox use for them.
Try Björn Karlsson's book: Beyond the C++ Standard Library: An Introduction to Boost. Its pretty straightforward and easy to grasp. I read this after I'd finished Scott Meyers three c++ books (effective series).
After reading Beyond the C++ Standard Library: An Introduction to Boost, I would recommend casually browsing the documentation on boost.org, just to get an idea of what's available. You can do a deep dive into a specific boost library when it looks like a good fit for a particular application.
I think shared_ptr sould be the easiest place to start .
Start using it inplaces of simple pointer or auto_ptr data types.
You can also look into weak_ptr.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 4 years ago.
Improve this question
Lots of the answers to C++ questions here contain the response:
"You should be using boost::(insert
your favourite smart pointer here) or
even better boost::(insert your
favourite mega complex boost type
here)"
I'm not at all convinced that this is doing any favours to the questioners who, by and large, are obvious C++ novices. My reasons are as follows:
Using smart pointers without
understanding what is going on under
the hood is going to lead to a
generation of C++ programmers who
lack some of the basic skills of a
programmer. Pretty much this seems to
have happened in the Java field
already.
Deciding which type of smart pointer
to use depends very much on the
problem domain being addressed. This
is almost always missing from the
questions posted here, so simply
saying "use a shared pointer" is
likely to be at the least unhelpful
and possibly totally wrong.
Boost is not yet part of the C++
standard and may not be available on
the specific platform the questioner
is using. Installing it is a bit
painful (I just did it using Jam) and
is way overkill if all you want are a
few smart pointers.
If you are writing FOSS code, you
don't want the code to be heavily
dependent on external libraries that,
once again, your users may not have.
I've been put off using FOSS code on
a number of occasions simply because
of the Byzantine complexity of the
dependencies between libraries.
To conclude, I'm not saying don't recommend Boost, but that we should be more careful when doing so.
Few points:
Using anything without understanding is considered harmful. But it is only the ignorant technology user (and his manager) who gets burned in the end.
You don't have to install boost to get the smart pointers - they are header only. And installation itself is rather straightforward, in the simplest approach just typing one or two commands.
Many of the Boost libraries and solutions are present in TR1 or will be present in C++0x
You will always depend on external libraries... Try to choose the one that have a bright future in terms of maintenance and support.
Unless you want to roll-out your custom solution - which would have some advantages and disadvantages.
C++ is not a novice-friendly language. With apologies to Scott Meyers, a beginner isn't learning just one language with C++, but four:
The C parts
Object Oriented parts: classes, inheritance, polymorphism, etc.
The STL: containers, iterators, algorithms
Templates and metaprogramming
I would argue that if the beginner is already climbing this mountain, they should be pointed towards the more "modern" aspects of C++ from the start. To do otherwise means that the beginner will learn C-ish C++ with regular pointers, resource leaks, etc. Find themselves in a world of pain, and then discover Boost and other libraries as a way to stem the hurt.
It's a complicated picture no matter what, so why not point them in a direction that has a positive pay-off for the invested mental efort?
As for dependencies, a great deal of Boost is header-only. And Boost's liberal license should permit its inclusion in just about any project.
Do you know how the compiler works ? Do you know how the OS works ? Do you know how the processor works ? Do you know how electronics works ? Do you know how electricity works ?
At some point you are using a black box, the question is, "is my ignorance problematic for what I am currently doing?".
If you have the taste for knowledge that's a great thing - and I clearly consider that a plus when interviewing engineers - but don't forget the finality of your work : build systems that solve problems.
I disagree. No-one would suggest that you should dive in to smart pointers without a thorough understanding of what's going on behind the scenes, but used sensibly they can remove a whole host of common errors. Moreover, Boost is high-quality production code from which a C++ novice can learn a great deal, in terms of design as much as implementation. It's not all hugely complicated, either, and you can pick and choose the bits you need.
It's impossible to understand everything thoroughly all the time. So take the word of many professional C++ developers for it that many parts of boost are indeed very useful things to use in your day-to-day development.
The inclusion of quite a lot of boost in C++0X is testament that even the team that manages the evolution of the language thinks that boost is a Good Thing (tm)
C++ is a weird, tough language. It's relatively easy to learn compared to how incredibly hard it is to master. There's some really arcane stuff you can do with it. Boost::mpl builds on some of those arcane things. I love boost, but I cringe every time I see someone in my organisation use boost::mpl. The reason: even quite seasoned C++ developers have trouble wrapping their head around how it works, and the code that uses it often reflects that (it ends up looking like someone banged code out until it worked). This is not a good thing, so I partially agree that some parts of boost should not be used without caution (boost::spirit is another example).
The C++ standard is also a weird thing. Most common compilers don't implement all of the existing standard (e.g. template exports). It's only a guideline of what to expect.
If your developer doesn't have the savvy to decide which smart pointer to use in a particular situation, perhaps they shouldn't be messing around in that part of the code without senior guidance.
There are always external libraries, starting with the run-time. A lot of boost is header-only so it does not introduce new external dependencies.
Quite frankly, for beginners I think boost isn't that well-suited. I think a beginner is better off understanding how the basics work before moving up the food chain using higher level tool/libs like boost or even STL. At the beginner stage it is not about productivity, it is about understanding. I think knowing how pointers work, being able for instance to manually create a linked list or sort one are part of the fundamentals that each programmer should learn.
I think boost is a great library. I love it. My favourite library is boost::bind and boost::function, which make function pointers much more flexible and easy-to-use. It fits in very well with different frameworks and keeps the code tidy.
I also use different Boost classes. For example, I use boost::graph to create graph classes and I use boost::filesystem for working with files inside directories.
However, boost is very complex. You need to be an experienced programmer to know its worth. Moreover, you need to have atleast some experience in C++ to understand how Boost works and implications of using Boost here or there.
Therefore, I would highly recommend looking at Boost for experienced programmers, especially if they are trying to re-invent the wheel (again). It can really be what it says on the tin: a boost towards your goal.
However, if you feel that the person asking a question is a beginner and tries to understand (for example) memory allocation, telling him to try boost smart pointers is a very bad idea. It's not helpful at all. The advantages of smart pointer classes, etc. can be comprehended only when the person experienced how standard memory allocation techniques work.
To finish off, Boost is not like learning to drive a car with automatic gearbox. It's like learning to drive on a F1 racing car.
I fully agree with you. It is the reason that i first explain them how it should be done (i.e when recommending boost::variant, i explain they should in general use a discriminated union. And i try not to say it's just a "magic boost thing" but show how they in principle implemented it. When i recommend boost::shared_ptr, i explain they would need to use a pointer - but it's better to use a smart pointer that has shared ownership semantics.). I try not to say just "use boost::xxx" when i see the questioner is a beginner. It is a language that's not just as simple to use as some scripting language. One has to understand the stuff one uses, because the language does not protect the programmer from doing bad things.
Of course it's not possible for novices to understand everything from the start on. But they should understand what their boost library solves and how it does it basically.
You can't compare this with learning processors or assembly language first. Similar it's not important to know how the bit-pattern of a null-pointer looks like. Knowledge of those are irrelevant in learning programming with C++. But pointers, array or any other basic things in C++ is not. One doesn't get around learning them before using [boost|std]::shared_ptr or [boost|std]::array successfully. These are things that has to be understood first in order to use the boost utilities successfully in my opinion. It's not about details like how to manually implement the pimpl-idiom using raw pointers - that's not the point I'm making. But the point is that one should first know basic things about pointers or the other parts a boost library helps with (for pointers, what they are and what they are good for, for example). Just look at the shared_ptr manual and try to get it without knowing about pointers. It's impossible.
And it's important to always point them to the appropriate boost manual. Boost manuals are high quality.
The consensus among almost all the answers is that boost is very valuable for experienced developers and for complex, real world, C++ software. I completely agree.
I also think that boost can be very valuable for beginners. Isn't it easier to use lexical_cast than to use ostringstream? Or to use BOOST_FOREACH instead of iterator syntax? The big problem is lack of good documentation of boost, especially for beginners. What is needed is a book that will tell you how to start with boost, which libraries are simple libraries that simplify tasks, and which libraries are more complex. Using these libraries together with good documentation will IMO make learning C++ easier.
We should encourage the use of standard canned libraries (and Boost is almost as standard as they get) whenever possible.
Some people seem to think that beginners should be taught the C side of C++ first, and then introduced to the higher-level stuff later. However, people tend to work as they're trained, so we're going to see a lot of production code written with badly managed raw pointers (well-managed raw pointers are awfully difficult sometimes), arrays (and the inevitable confusion between delete and delete []), and stuff like that. I've worked with code like that. I don't want to do it again any more than I have to.
Start beginners off with the way you want them writing code. This means teaching them about the STL containers and algorithms and some of the Boost libraries at first, so the first thing they think about when needing a group of things is a vector<>. Then teach them the lower-level constructs, so they'll know about them (or where to look them up) when they encounter them, or on the very rare occasions when they need to micro-optimize.
There's basically two types of programmers: the coders, who should be taught languages the way they should be writing them, and the enthusiast, who will learn the low-level stuff, including principles of operating systems, C, assembly code, and so on. Both are well served by learning the language they're going to use up front, while only the enthusiasts will be well served by learning from some arbitrary level of fundamentals.
I think you are mixing a lot of different concerns, not all of them related to Boost specifically:
First, should programmers (or C++ novices specifically) be encouraged to use libraries, idioms, paradigms, languages or language features they don't understand?
No, of course not. Every programmer should understand the tools they use, especially in a language like C++. However, I don't see a lot of questions here on SO where people are encouraged to not understand the code they're using. When people say they want to do X in C++, I think it's find to say "Boost has an implementation of X which works, which is more than a homebrewed solution would do, so use that".
Of course if the question is "how does X work", the question can't be answered with "use Boost's implementation". But I really don't see the problem in recommending Boost for the former kind of questions.
I also don't see how it's even possible to use Boost without understanding what's going on under the hood. C++, with or without Boost, is not Java. Using Boost in no way protects you from the complexities of the language. You still have to worry about copy constructors, pointer arithmetics, templates and everything else that can blow up in your face.
This is nothing like what happened in Java. They designed a language that removed all the subtleties. Boost doesn't do that. Quite the contrary, it has pioneered new idioms and techniques in generic programming. Using Boost is not always simple.
About the availability of Boost, I think that's a non-issue. It is available on the platforms used in the vast majority of questions, and if they're not able to use Boost, the suggestion is still not harmful, just useless.
Further, most Boost libraries are header-only and don't require you to install the whole thing. If you only want smart pointers, simply include those headers and nothing else.
About FOSS, you have a point in some cases But I'd say this is a problem for less universal libraries that users do not have. But Boost is extremely common, and if people don't have it, they should get it, as it is applicable to pretty much any problem domain. And of course, the license is compatible with any FOSS project you care to mention.
I'd rather work on a OSS project that used Boost to do the heavy lifting than one which reinvented its own (buggy and proprietary) wheels, with steep learning curves that could have been avoided.
So yeah, in some cases, recommending Boost is unhelpful. But I don't see how it can be harmful.
In any case, I don't see how it can be even half as harmful as teaching novices to roll their own. In C++, that's a recipe for disaster. It's the sole reason why C++ still has a reputation for being error-prone and produce buggy software. Because for far too long, people wrote everything from scratch themselves, distrusting the standard library, distrusting 3rd party code, distrusting everything that wasn't legal in C.
I'm not at all convinced that this is doing any favours to the questioners who, by and large, are obvious C++ novices. ...:
Using smart pointers without understanding what is going on under the hood is going to lead to a generation of C++ programmers who lack some of the basic skills of a programmer.
Do we tell novice programmers that they must learn assembly language before they get to read up on modern programming languages? They clearly don't know what's going on under the hood otherwise.
Should "Hello World" include an implementation of the I/O subsystem?
Personally I learned how to construct objects before I learned how to write classes. I think I learned how to use STL vectors before I learned C-style arrays. I think it's the right approach: "here's how to refer to several nearly identical variables using a std::vector, later I'll show you what's swept under the rug via C-style arrays and new[] and delete[]."
I disagree. Of course you will always know more about the internal workings of everything when coding it from scratch than when using 3rd party libraries. But time and money are limited, and using good 3rd party libraries such as boost is a very good way to save your resources.
I can see your point, but understanding something does not mean that you have to rewrite everything from scratch.
They are not "standard" but they are as standard as a library can get.
It is true that deploying them can be painful (but not all of the sublibraries require compilation); on the other hand they do not have further dependencies on their own, so I wouldn't be too worried about that part neither.
I agree with you, high level libraries hide things from you. It might be a good idea in the short run, but in the long run, the novice will have severe gaps in their understanding of the language.
It's easy for us non-novices to say "just use this library" because we've been down that long hard road of learning things the hard way, and naturally we want to save someone else the trouble of doing the same.
Novices SHOULD have to struggle with rolling their own low-level solutions to problems. And then, when they've got a better understanding of how their own solution worked, they can use the third-party solution, confident that they have some idea of what's going on under the hood. They'll use that library better!
I think this is a broader subject than just being about Boost. I completely regret picking up VB as my first language. If I had just started with ugly, hard to learn c, I'd be years ahead of where I am now.
I would agree with the point about smart pointers. I am a C++ beginner, and when asking a simple question about pointer syntax, one answer suggested smart pointers were the way to go. I know I'm not ready for boost (I'm not really ready for the STL either), so in most cases I steer myself away from that type of suggestion.
Scoped and dynamic resource ownership are general basic neeeds and boost's implementation of'em is very good an highly recommended. I use them a lot and they work fine.
Boost is a great library. I really hope that it grows in breadth and acceptance. Use it, extend it, and promote it.
One of the great things about the .NET community is that it has a great base class library. One of the fundemental problems with C++, I believe, is the minimalistic C++ standard library. Anywhere you go to develop code, FOSS or corporate, there is some selection of libraries that are used since there isn't a broad standard library. So you end up being a INSERT_YOUR_COMPANY_HERE C++ programmer and not necessarily too transferrable. Yes, you design/architecture skills transfer, but there is the learning curve with picking up familiarity with whatever set of libraries the next place is using. Where as a .NET developer will basically be using the same class library and can hit the ground running. Also, the libraries that are built (and reused) have a broader base to build on.
Just as an aside, you can use http://codepad.org for a code paste bin and it supports boost!
I have worked for companies who have viewed boost as library to avoid due in part to its past reputation as a poorly managed project. I know things have changed with the project, but commercial projects who want to use boost must be aware of the source of the code contained in the library, or at least be assured that they're not going to be liable for IP or patent infringements.
Sadly, the library has this reputation and it will take a while for it to break before it sees wide use in the commercial sector. I also feel this is a reason not to recommend it blindly.
I am considering the possibility of designing an application that would allow people to develop C++ code graphically. I was amazed when I discovered Scratch (see site and tutorial videos).
I believe most of C++ can be represented graphically, with the exceptions of preprocessor instructions and possibly function pointers.
What C++ features do you think could be (or not be) represented by graphical items?
What would be the pros and cons of such an application ? How much simpler would it be than "plain" C++?
RECAP and MORE:
Pros:
intuitive
simple for small applications
helps avoid typos
Cons:
may become unreadable for large (medium?) - sized applications
manual coding is faster for experienced programmers
C++ is too complicated a language for such an approach
Considering that we -at my work- already have quite a bit of existing C++ code, I am not looking for a completely new way of programming. I am considering an alternate way of programming that is fully compatible with legacy code. Some kind of "viral language" that people would use for new code and, hopefully, would eventually use to replace existing code as well (where it could be useful).
How do you feel towards this viral approach?
When it comes to manual vs graphical programming, I tend to agree with your answers. This is why, ideally, I'll find a way to let the user always choose between typing and graphical programming. A line-by-line parser (+partial interpreter) might be able to convert typed code into graphical design. It is possible. Let's all cross our fingers.
Are there caveats to providing both typing and graphical programming capabilities that I should think about and analyze carefully?
I have already worked on template classes (and more generally type-level C++) and their graphical representation.
See there for an example of graphical representation of template classes. Boxes represent classes or class templates. First top node is the class itself, the next ones (if any) are typedef instructions inside the class. Bottom nodes are template arguments. Edges, of course, connect classes to template arguments for instantiations.
I already have a prototype for working on such type-level diagrams.
If you feel this way of representing template classes is plain wrong, don't hesitate to say so and why!
Much as I like Scratch, it is still much quicker for an experienced programmer to write code using a text editor than it is to drag blocks around, This has been proved time and again with any number of graphical programming environments.
Writing code is the easiest part of a developers day. I don't think we need more help with that. Reading, understanding, maintaining, comparing, annotating, documenting, and validating is where - despite a gargantuan amount of tools and frameworks - we still are lacking.
To dissect your pros:
Intuitive and simple for small applications - replace that with "misleading". It makes it look simple, but it isn't: As long as it is simple, VB.NET is simpler. When it gets complicated, visual design would get in the way.
Help avoid typos - that's what a good style, consistency and last not least intellisense are for. The things you need anyway when things aren't simple anymore.
Wrong level
You are thinking on the wrong level: C++ statements are not reusable, robust components, they are more like a big bag of gears that need to be put together correctly. C++ with it's complexity and exceptions (to rules) isn't even particulary suited.
If you want to make things easy, you need reusable components at a much higher level. Even if you have these, plugging them together is not simple. Despite years of struggle, and many attempts in many environments, this sometimes works and often fails.
Viral - You are correct IMO about that requriement: allow incremental adoption. This is closely related to switching smoothly between source code and visual representation, which in turn probably means you must be able to generate the visual representation from modified source code.
IDE Support - here's where most language-centered approaches go astray. A modern IDE is more than just a text editor and a compiler. What about debugging your graph - with breakpoints, data inspection etc? Will profilers, leak detectors etc. highlight nodes in your graph? Will source control give me a Visual Diff of yesterday's graph vs. today's?
Maybe you are on to something, despite all my "no"s: a better way to visualize code, a way to put different filters on it so that I see just what I need to see.
The early versions of C++ were originally written so that they compiled to C, then the C was compiled as normal.
What it sounds like you are describing is a graphical language that is compiled to C++, which will then be compiled as normal.
So really you are not creating a graphical C++, you are creating a new language that happens to be graphical. Nothing wrong with that, but don't let C++ restrict what you do, because eventually you may want to compile the graphical language straight to machine code, or even to something like CIL, Java ByteCode, or whatever else tickles your fancy.
Other graphical languages you may want to check out are LabVIEW, and more generally the category of visual programming languages.
Good luck in your efforts.
The complexity of a nontrivial program is usually too high to be represented with graphical symbols, which are low in their information content. Unless your approach is markedly different in some way, I am skeptical that this would be of value based on past efforts.
So, practically speaking, his will be useful only for instructional purposes and very simple programs. But that would still be a great target market for a product like this. sometimes people have trouble grasping the fundamentals, and a visual model might be just the thing to help things click.
Interesting idea. I doubt I'd use it though. I tend to prefer coding in a flat text editor, not even an IDE, and for tough problems I prefer a pad of paper. Most of the really experienced programmers I know work this way, Maybe it's because we grew up in a different environment, but I think it's also because of the way we think about programming. As you get more experience, you start seeing the code in your head more clearly than any GUI tool will show it to you.
As for your question, I'd nominate templates as one of the harder / more interesting sort of thing to try to represent well. They are ubiquitous and carry information that you won't have access to as you are designing your tool. Getting that to the user in a useful way should pose an interesting challenge.
What C++ features do you think could be [...] represented by graphical items?
Object Oriented Design. Hence classes, inheritance, polymorphism, mutability, const-ness etc. And, templates.
What would be the pros and cons of such an application?
It may be easier for beginners to start writing programs. For the experienced, it may be get rid of the boring parts of programming.
Think of any other code generator. They create a framework for you to write the more involved portion(s). They also lead to bloated-code (think of any WYSIWYG HTML editor).
The biggest challenge, as I see it, is that any such UI necessarily hinders the user's imagination.
How much simpler would it be than "plain" c++ ?
It can be a real pain, when you wade through truckloads of errors which is typical of code generators.
Further, since a lot of code is generated, you have no idea of what is going on -- debugging becomes difficult.
Also, for the experienced there may be some irritation to find that the generated code is not per their preferred coding style.
I prefer hot-keys instead graphical menus and buttons.
And I think same thing will happen with graphical development tool. Many peoples will prefer manual codding.
But, source code visualizer - should be nice thing.
I like the idea, but I suspect there comes a point where things get far too complicated to be represented graphically.
However, given recent experience at work; it would be useful to give such a graphical interface to a non-techie person to use to create basic drag-and-drop programs, leaving myself free to get on with some "proper" programming ;-) If it can do the job of allowing somebody non-skilled to build something functional it can be a very good thing (even if programming logic escapes them)
There comes a point in such a system where it becomes easier to define what you want to do using literal C++ code, rather than have a user interface getting in the way; it can get frustrating to the sessioned programmer knowing the precise code that needs to be written but then only being limited to the design GUI. I'm specifically thinking about a more common application, such as html editors/designers in which they allow newbies to build their websites without knowing any html at all.
It would be interesting to see how such a system would handle the dynamic allocation of memory, and the different states of a program as time progressed; I suspect that there are some very basic programming concepts that may be difficult to represent graphically.. Polymorphism..? Virtual Classes, LinkList, Stacks/Circular Queues. I wonder for a moment how you would explain an image compression algorithm (such as jpg) successfully too without the help of a gigantic display screen.
I also wonder if such a system would even go to such a low level, and whether you would be dealing with abstracted concepts and the compiler would be working out the best way to do something.
I've been working on a new model-driven software development paradigm named ABSE (http://www.abse.info) that supports end-user programming: It's a template-based system that can be complemented with transformation code. I also have an IDE (named AtomWeaver) implementing ABSE that is in pre-alpha stage right now.
With AtomWeaver, as an expert/architect, you build your knowledge Templates, and then the developers (or end-users if you make your meta-models simpler) can just "assemble" systems by building blocks, and then filling template parameters in form-style editors.
At the end, pressing the "Generate" button will create the final system as specified by the architect/expert.
I'm surprised you think function pointers would be a particular problem. How about anything at all to do with pointers?
A programming language can be represented by a hierarchy of nodes - that's exactly what the compiler turns it into. It is very strange that the UI for editing programs is still a sequence of characters that get parsed, because the degrees of freedom in the editor is way larger than the available set of allowed choices. But intellisense helps to reduce this problem a lot.
C++ would be a strange choice to base such a system on.
I think the major problem of this kind of IDEs are that the code generated becomes unmantainable easily.
This happened to Delphi. It's a really nice tool to develop some kind of applications, however, when we start adding complex relationships between the components, start adding Design Patterns, etc. the code grows to an unmantainable size.
I believe it's also because graphical tools don't apply the concept of MVC (or if they do, it's only in the way that the IDE understands).
It can be really helpful for prototypes and very small applications that don't tend to grow, otherwise it can become a mess for the developer(s)
How would you go about converting a reasonably large (>300K), fairly mature C codebase to C++?
The kind of C I have in mind is split into files roughly corresponding to modules (i.e. less granular than a typical OO class-based decomposition), using internal linkage in lieu private functions and data, and external linkage for public functions and data. Global variables are used extensively for communication between the modules. There is a very extensive integration test suite available, but no unit (i.e. module) level tests.
I have in mind a general strategy:
Compile everything in C++'s C subset and get that working.
Convert modules into huge classes, so that all the cross-references are scoped by a class name, but leaving all functions and data as static members, and get that working.
Convert huge classes into instances with appropriate constructors and initialized cross-references; replace static member accesses with indirect accesses as appropriate; and get that working.
Now, approach the project as an ill-factored OO application, and write unit tests where dependencies are tractable, and decompose into separate classes where they are not; the goal here would be to move from one working program to another at each transformation.
Obviously, this would be quite a bit of work. Are there any case studies / war stories out there on this kind of translation? Alternative strategies? Other useful advice?
Note 1: the program is a compiler, and probably millions of other programs rely on its behaviour not changing, so wholesale rewriting is pretty much not an option.
Note 2: the source is nearly 20 years old, and has perhaps 30% code churn (lines modified + added / previous total lines) per year. It is heavily maintained and extended, in other words. Thus, one of the goals would be to increase mantainability.
[For the sake of the question, assume that translation into C++ is mandatory, and that leaving it in C is not an option. The point of adding this condition is to weed out the "leave it in C" answers.]
Having just started on pretty much the same thing a few months ago (on a ten-year-old commercial project, originally written with the "C++ is nothing but C with smart structs" philosophy), I would suggest using the same strategy you'd use to eat an elephant: take it one bite at a time. :-)
As much as possible, split it up into stages that can be done with minimal effects on other parts. Building a facade system, as Federico Ramponi suggested, is a good start -- once everything has a C++ facade and is communicating through it, you can change the internals of the modules with fair certainty that they can't affect anything outside them.
We already had a partial C++ interface system in place (due to previous smaller refactoring efforts), so this approach wasn't difficult in our case. Once we had everything communicating as C++ objects (which took a few weeks, working on a completely separate source-code branch and integrating all changes to the main branch as they were approved), it was very seldom that we couldn't compile a totally working version before we left for the day.
The change-over isn't complete yet -- we've paused twice for interim releases (we aim for a point-release every few weeks), but it's well on the way, and no customer has complained about any problems. Our QA people have only found one problem that I recall, too. :-)
What about:
Compiling everything in C++'s C subset and get that working, and
Implementing a set of facades leaving the C code unaltered?
Why is "translation into C++ mandatory"? You can wrap the C code without the pain of converting it into huge classes and so on.
Your application has lots of folks working on it, and a need to not-be-broken.
If you are serious about large scale conversion to an OO style, what
you need is massive transformation tools to automate the work.
The basic idea is to designate groups of data as classes, and then
get the tool to refactor the code to move that data into classes,
move functions on just that data into those classes,
and revise all accesses to that data to calls on the classes.
You can do an automated preanalysis to form statistic clusters to get some ideas,
but you'll still need an applicaiton aware engineer to decide what
data elements should be grouped.
A tool that is capable of doing this task is our DMS Software Reengineering
Toolkit.
DMS has strong C parsers for reading your code, captures the C code
as compiler abstract syntax trees, (and unlike a conventional compiler)
can compute flow analyses across your entire 300K SLOC.
DMS has a C++ front end that can be used as the "back" end;
one writes transformations that map C syntax to C++ syntax.
A major C++ reengineering task on a large avionics system gives
some idea of what using DMS for this kind of activity is like.
See technical papers at
www.semdesigns.com/Products/DMS/DMSToolkit.html,
specifically
Re-engineering C++ Component Models Via Automatic Program Transformation
This process is not for the faint of heart. But than anybody
that would consider manual refactoring of a large application
is already not afraid of hard work.
Yes, I'm associated with the company, being its chief architect.
I would write C++ classes over the C interface. Not touching the C code will decrease the chance of messing up and quicken the process significantly.
Once you have your C++ interface up; then it is a trivial task of copy+pasting the code into your classes. As you mentioned - during this step it is vital to do unit testing.
GCC is currently in midtransition to C++ from C. They started by moving everything into the common subset of C and C++, obviously. As they did so, they added warnings to GCC for everything they found, found under -Wc++-compat. That should get you on the first part of your journey.
For the latter parts, once you actually have everything compiling with a C++ compiler, I would focus on replacing things that have idiomatic C++ counterparts. For example, if you're using lists, maps, sets, bitvectors, hashtables, etc, which are defined using C macros, you will likely gain a lot by moving these to C++. Likewise with OO, you'll likely find benefits where you are already using a C OO idiom (like struct inheritence), and where C++ will afford greater clarity and better type checking on your code.
Your list looks okay except I would suggest reviewing the test suite first and trying to get that as tight as possible before doing any coding.
Let's throw another stupid idea:
Compile everything in C++'s C subset and get that working.
Start with a module, convert it in a huge class, then in an instance, and build a C interface (identical to the one you started from) out of that instance. Let the remaining C code work with that C interface.
Refactor as needed, growing the OO subsystem out of C code one module at a time, and drop parts of the C interface when they become useless.
Probably two things to consider besides how you want to start are on what you want to focus, and where you want to stop.
You state that there is a large code churn, this may be a key to focus your efforts. I suggest you pick the parts of your code where a lot of maintenance is needed, the mature/stable parts are apparently working well enough, so it is better to leave them as they are, except probably for some window dressing with facades etc.
Where you want to stop depends on what the reason is for wanting to convert to C++. This can hardly be a goal in itself. If it is due to some 3rd party dependency, focus your efforts on the interface to that component.
The software I work on is a huge, old code base which has been 'converted' from C to C++ years ago now. I think it was because the GUI was converted to Qt. Even now it still mostly looks like a C program with classes. Breaking the dependencies caused by public data members, and refactoring the huge classes with procedural monster methods into smaller methods and classes never has really taken off, I think for the following reasons:
There is no need to change code that is working and that does not need to be enhanced. Doing so introduces new bugs without adding functionality, and end users don't appreciate that;
It is very, very hard to do refactor reliably. Many pieces of code are so large and also so vital that people hardly dare touching it. We have a fairly extensive suite of functional tests, but sufficient code coverage information is hard to get. As a result, it is difficult to establish whether there are already sufficient tests in place to detect problems during refactoring;
The ROI is difficult to establish. The end user will not benefit from refactoring, so it must be in reduced maintenance cost, which will increase initially because by refactoring you introduce new bugs in mature, i.e. fairly bug-free code. And the refactoring itself will be costly as well ...
NB. I suppose you know the "Working effectively with Legacy code" book?
You mention that your tool is a compiler, and that: "Actually, pattern matching, not just type matching, in the multiple dispatch would be even better".
You might want to take a look at maketea. It provides pattern matching for ASTs, as well as the AST definition from an abstract grammar, and visitors, tranformers, etc.
If you have a small or academic project (say, less than 10,000 lines), a rewrite is probably your best option. You can factor it however you want, and it won't take too much time.
If you have a real-world application, I'd suggest getting it to compile as C++ (which usually means primarily fixing up function prototypes and the like), then work on refactoring and OO wrapping. Of course, I don't subscribe to the philosophy that code needs to be OO structured in order to be acceptable C++ code. I'd do a piece-by-piece conversion, rewriting and refactoring as you need to (for functionality or for incorporating unit testing).
Here's what I would do:
Since the code is 20 years old, scrap down the parser/syntax analyzer and replace it with one of the newer lex/yacc/bison(or anything similar) etc based C++ code, much more maintainable and easier to understand. Faster to develop too if you have a BNF handy.
Once this is retrofitted to the old code, start wrapping modules into classes. Replace global/shared variables with interfaces.
Now what you have will be a compiler in C++ (not quite though).
Draw a class diagram of all the classes in your system, and see how they are communicating.
Draw another one using the same classes and see how they ought to communicate.
Refactor the code to transform the first diagram to the second. (this might be messy and tricky)
Remember to use C++ code for all new code added.
If you have some time left, try replacing data structures one by one to use the more standardized STL or Boost.
After switching from C++ to C++ w/boost, do you think your OOD skills improved?
Do you notice patterns in "Normal" C++ code that you wouldn't consider that you've switched, or do you find that it enables a more abstract design?
I guess I'm really wondering if you just use it as a tool, or if you change your entire approach to OO design to make more efficient use of objects when using boost pointers.
Edit:summary
This question was kind of strange--I was asking because I've run into so much C++ code that was not at all OO. I'm fairly sure (with that and my work on it before moving to a managed language) that it's harder to think in OO in C++ than a managed language.
From looking at these posts, I'm guessing that you learn the value of OO before finding a need for a better way to manage memory, so by the time you start looking for something like Boost, you're already using OO methodologies pretty heavily.
I was kind of expecting a bunch of answers saying that it helped them think in OO, but now that I think about it, if you aren't using OO, boost pointers are not very helpful, and you wouldn't see the need for them (so you wouldn't have replied).
In a project in C++ I was doing about six years ago, we implemented our own boost-like automatic pointer scheme. It worked pretty well, except for the various bugs in it. (Sure wish we had used boost...)
Nonetheless, it really didn't change how we developed code. Object oriented design, with or without managed pointers, is very similar. There's times when you need to return objects, or times when pointers to objects are more important. The nice thing about smart pointers has only a small amount to do with how you design your application. Instead of passing a potentially dangerous memory leak around, you can pass that same data and be fairly certain that it's not going to leak.
In that respect, there are some things you can tend to do more with smart pointers: simplify your code. Instead of returning integers or basic structures every where, you can more freely pass complicated data structures or classes without worry. You can build more complex apps, faster, without having to worry so much. It lets you have the raw power of C and C++ when you need it (why would you be using C or C++ if you didn't need it?) and have the ease of memory management that's such an amazing productivity boost. If automatically managed memory wasn't useful, it wouldn't be in almost every other language on the planet!
STL/Boost is a tool for the job. They help me implement my ideas not the other way around. Clarification: Boost did not boost up my OOD skills.
It has deeply changed my way of coding, and i'm spreading the word. Through the use of Boost.Graph and Boost.PropertyMap in particular, i realized that i could write "true" algorithms in a simple class, not (yet) knowing how to access information, not even knowing (or caring) what sub-actions might be done while executing the algorithm.
My team is now designing complex computing functionality using a graphical tool.
One might argue that templates are really the base of this change, but Boost clearly paved the way. To me, discovering new Boost libraries is very often a great opportunity to learn important stuff that can be applied to our everyday work !
Once I discovered boost::bind (and boost::function) I found instead of thinking in terms of inheritance and abstract base classes ("interfaces" in java/c#-speak) I started seeing everything as a functor.
For example, pre-boost I'd have built a menu system where the menus were containers of IActionable* items and anything which wanted to be hooked into the menu system would have to inherit IActionable and provide an action method. Post-boost and I'm implementing menus containing boost::function<void()> objects and just throwing anything I want into them using boost::bind.
Another thing: just looking at the way in which boost successfully employs templates really made me raise my expectations of what was possible with them and make the effort to make better use of them in my own code, so I'm writing a lot more "generic" and less "OOP" code.
The smart pointers are certainly useful and get a lot of coverage, but apart from cleaning up some explicit deletes they're hardly a paradigm shift.
For me, it didn't change the way I do design, but Boost does give me additional tools so that certain things are easier. For example, with "smart" pointers, I no longer have to think about making sure certain object creations have to destroyed at the proper time (mostly in the exceptional case). But like any tool, I have to understand when to use them and when NOT to.