Assume I have a Haskell module named Foo, defined in src/Foo.hs. Assume also that Foo exports a type Bar.
Now I want to write unit tests for Bar (for the whole Foo module, actually), so I throw a couple of QuickCheck properties into test/FooTest.hs; but hey, now I need to define an Arbitrary instance for Bar.
And there's the rub: in -Wall -Werror mode, ghc requires instance declarations to appear in one of two places: in the same file where the type is defined, or where the class is defined. But I don't want to clutter my Foo module with a build dependency on QuickCheck, and I obviously cannot add an instance of Bar to QuickCheck.
So how do I make my datatype an instance of Arbitrary, for the purpose of unit testing only, without introducing a dependency on QuickCheck for users of my module and without tossing-Wall -Werror out of the window?
Within the test suite, create a newtype which wraps Bar and define the Arbitrary instance for the newtype.
Try ghc -Wall -Werror -Wno-orphans for the test module.
Not exactly perfect since it will disable the warning for other orphan instances, but I believe it's the closest we can get at the moment.
Having a "suppress this warning in the next line" pragma would also be nice.
You can conditionally define a TESTING CPP macro when you're compiling the test suite. This lets you avoid orphans but only incur the dependency when you use it. You can see a similar use of such a macro in the containers package, but that package currently uses orphan instances for the specific purpose of adding Arbitrary instances to the test suite. I may change that soon.
Related
Now, I implemented a factory class to dynamically create class with a idenification string, please see the following code:
void IOFactory::registerIO()
{
Register("NDAM9020", []() -> IOBase * {
return new NDAM9020();
});
Register("BK5120", []() -> IOBase * {
return new BK5120();
});
}
std::unique_ptr<IOBase> IOFactory::createIO(std::string ioDeviceName)
{
std::unique_ptr<IOBase> io = createObject(ioDeviceName);
return io;
}
So we can create the IO class with the registered name:
IOFactory ioFactory;
auto io = ioFactory.createIO("BK5120");
The problem with this method is if we add another IO component, we should add another register code in registerIO function and compile the whole project again. So I was wondering if I could dynamically register class from a configure file(see below) at runtime.
io_factory.conf
------------------
NDAM9020:NDAM9020
BK5120:BK5120
------------------
The first is identification name and the second is class name.
I have tried with Macros, but the parameter in Macros cann't be string. So I was wondering if there is some other ways. Thanks for advance.
Update:
I didn't expect so many comments and answers, Thank you all and sorry for replying late.
Our current OS is Ubuntu16.04 and we use the builtin compiler that is gcc/g++5.4.0, and we use CMake to manage the build.
And I should mention that it is not a must that I should register class at runtime period, it is also OK if there is a way to do this in compile period. What I want is just avoiding the recompiling when I want to register another class.
So I was wondering if I could dynamically register class from a configure file(see below) at runtime.
No. As of C++20, C++ has no reflection features allowing it. But you could do it at compile time by generating a simple C++ implementation file from your configuration file.
How to dynamically register class in a factory class at runtime period with c++
Read much more about C++, at least a good C++ programming book and see a good C++ reference website, and later n3337, the C++11 standard. Read also the documentation of your C++ compiler (perhaps GCC or Clang), and, if you have one, of your operating system. If plugins are possible in your OS, you can register a factory function at runtime (by referring to to that function after a plugin providing it has been loaded). For examples, the Mozilla firefox browser or recent GCC compilers (e.g. GCC 10 with plugins enabled), or the fish shell, are doing this.
So I was wondering if I could dynamically register class from a configure file(see below) at runtime.
Most C++ programs are running under an operating system, such as Linux. Some operating systems provide a plugin mechanism. For Linux, see dlopen(3), dlsym(3), dlclose(3), dladdr(3) and the C++ dlopen mini-howto. For Windows, dive into its documentation.
So, with a recent C++ implementation and some recent operating systems, y ou can register at runtime a factory class (using plugins), and you could find libraries (e.g. Qt or POCO) to help you.
However, in pure standard C++, the set of translation units is statically known and plugins do not exist. So the set of functions, lambda-expressions, or classes in a given program is finite and does not change with time.
In pure C++, the set of valid function pointers, or the set of valid possible values for a given std::function variable, is finite. Anything else is undefined behavior. In practice, many real-life C++ programs accept plugins thru their operating systems or JIT-compiling libraries.
You could of course consider using JIT-compiling libraries such as asmjit or libgccjit or LLVM. They are implementation specific, so your code won't be portable.
On Linux, a lot of Qt or GTKmm applications (e.g. KDE, and most web browsers, e.g. Konqueror, Chrome, or Firefox) are coded in C++ and do load plugins with factory functions. Check with strace(1) and ltrace(1).
The Trident web browser of MicroSoft is rumored to be coded in C++ and probably accepts plugins.
I have tried with Macros, but the parameter in Macros can't be string.
A macro parameter can be stringized. And you could play x-macros tricks.
What I want is just avoiding the recompiling when I want to register another class.
On Ubuntu, I recommend accepting plugins in your program or library
Use dlopen(3) with an absolute file path; the plugin would typically be passed as a program option (like RefPerSys does, or like GCC does) and dlopen-ed at program or library initialization time. Practically speaking, you can have lots of plugins (dozen of thousands, see manydl.c and check with pmap(1) or proc(5)). The dlsym(3)-ed C++ functions in your plugins should be declared extern "C" to disable name mangling.
A single C++ file plugin (in yourplugin.cc) can be compiled with g++ -Wall -O -g -fPIC -shared yourplugin.cc -o yourplugin.so and later you would dlopen "./yourplugin.so" or an absolute path (or configure suitably your $LD_LIBRARY_PATH -see ld.so(8)- and pass "yourplugin.so" to dlopen). Be also aware of Rpath.
Consider also (after upgrading your GCC to GCC 9 at least, perhaps by compiling it from its source code) using libgccjit (it is faster than generating temporary C++ code in some file and compiling that file into a temporary plugin).
For ease of debugging your loaded plugins, you might be interested by Ian Taylor's libbacktrace.
Notice that your program's global symbols (declared as extern "C") can be accessed by name by passing a nullptr file path to dlopen(3), then using dlsym(3) on the obtained handle. You want to pass -rdynamic -ldl when linking your program (or your shared library).
What I want is just avoiding the recompiling when I want to register another class.
You might registering classes in a different translation unit (a short one, presumably). You could take inspiration from RefPerSys multiple #include-s of its generated/rps-name.hh file. Then you would simply recompile a single *.cc file and relink your entire program or library. Notice that Qt plays similar tricks in its moc, and I recommend taking inspiration from it.
Read also J.Pitrat's book on Artificial Beings: the Conscience of a Conscious Machine ISBN which explains why a metaprogramming approach is useful. Study the source code of GCC (or of RefPerSys), use or take inspiration from SWIG, ANTLR, GNU bison (they all generate C++ code) when relevant
You seem to have asked for more dynamism than you actually need. You want to avoid the factory itself having to be aware of all of the classes registered in it.
Well, that's doable without going all the way runtime code generation!
There are several implementations of such a factory; but I am obviously biased in favor of my own: einpoklum's Factory class (gist.github.com)
simple example of use:
#include "Factory.h"
// we now have:
//
// template<typename Key, typename BaseClass, typename... ConstructionArgs>
// class Factory;
//
#include <string>
struct Foo { Foo(int x) { }; }
struct Bar : Foo { Bar(int x) : Foo(x) { }; }
int main()
{
util::Factory<std::string, Foo, int> factory;
factory.registerClass<Bar>("key_for_bar");
auto* my_bar_ptr factory.produce("key_for_bar");
}
Notes:
The std::string is used as a key; you could have a factory with numeric values as keys instead, if you like.
All registered classes must be subclasses of the BaseClass value chosen for the factory. I believe you can change the factory to avoid that, but then you'll always be getting void *s from it.
You can wrap this in a singleton template to get a single, global, static-initialization-safe factory you can use from anywhere.
Now, if you load some plugin dynamically (see #BasileStarynkevitch's answer), you just need that plugin to expose an initialization function which makes registerClass() class calls on the factory; and call this initialization function right after loading the plugin. Or if you have a static-initialization safe singleton factory, you can make the registration calls in a static-block in your plugin shared library - but be careful with that, I'm not an expert on shared library loading.
Definetly YES!
Theres an old antique post from 2006 that solved my life for many years. The implementation runs arround having a centralized registry with a decentralized registration method that is expanded using a REGISTER_X macro, check it out:
https://web.archive.org/web/20100618122920/http://meat.net/2006/03/cpp-runtime-class-registration/
Have to admit that #einpoklum factory looks awesome also. I created a headeronly sample gist containing the code and a sample:
https://gist.github.com/h3r/5aa48ba37c374f03af25b9e5e0346a86
I am working on creating a package with two new commands, say foo and bar.
For example, if foo.ado contains:
program define foo
...
rex
end
program define rex
...
end
But my other command, bar.ado, also needs to call rex. Where should I put rex?
I see the following few options:
Create a rex.ado file as well.
Create a rex.do file and include it from within both foo.ado and bar.ado using include "`c(sysdir_plus)'r/rex.do" at the bottom of each file.
Copy the code into both foo.ado and bar.ado, which seems ugly because now the code must be maintained in two places.
What is best practice for organizing subroutines that are needed by both foo and bar?
Also, should the subroutine be called rex, _rex, or something else — maybe _foobar_rex — to indicate it is actually a sub-command that foo and bar depend on to work correctly rather than a separate command intended to stand on its own?
Create a rex.ado file as well
Your question is a bit too broad. Personally, I would go with the first option to be safe, although it really depends on the structure of your project. Sometimes including rex in a single ado file may be enough. This will be the case, for example, if foo is a wrapper command. However, for most other use cases, including two commands sharing a common program, i strongly believe that you will need to have a separate ado file.
The second option is obviously unnecessary, since the first does the same thing, plus it does not have to load the program every single time you call it. The third option is probably the worst in a programming context, as it may create conflicts and will be difficult to maintain down the road.
With regards to naming conventions, I would recommend using something like _rex only if you include the program as a subroutine in an ado file. Otherwise, rex will do just fine and will also indicate that the program has a wider scope within your project. It is also better, in my opinion, to provide a more elaborate explanation about the intended use of rex using a comment at the start of the ado file, rather than trying to incorporate this in the name.
I working on a huge code base written many years ago. We're trying to implement multi-threading and I'm incharge of cleaning up global variables (sigh!)
My strategy is to move all global variables to a class, and then individual threads will use instances of that class and the globals will be accessed through class instance and -> operator.
In first go, I've compiled a list of global variables using nm by finding B and D group object names. The list is not complete, and incase of static variables, I don't get file and line number info.
The second stage is even more messy, I've to replace all globals in the code base with classinstance->global_name pattern. I'm using cscope Change text string for this. The problem is that in case of some globals, their name is also being used locally inside functions, and thus cscope is replacing them as well.
Any other way to go about it? Any strategies, or help please!
just some suggestions, from my experience:
use eclipse: the C++ indexer is very good, and when dealing with a large project I find it very useful to track variables. shift+ctrl+g (I have forgotten how to access to it from menus!) let you search all the references, ctrl+alt+h (open call hierarchy) the caller-callee trees...
use eclipse: it has good refactoring tools, that is able to rename a variable without touching same-name-different-scope variables. (it often fails in case there are templates involved. I find it good, better than visual studio 2008 counterpart).
use eclipse: I know, it get some time to get started with it, but after you get it, it's very powerful. It can deal easily with the existing makefile based project (file -> new -> project -> makefile project with existing code).
I would consider not to use class members, but accessors: it's possibile that some of them will be shared among threads, and need some locking in order to be properly used. So I would prefer: classinstance->get_global_name()
As a final note, I don't know whether using the eclipse indexer at command-line would be helpful for your task. You can find some examples googling for it.
This question/answer can give you some more hints: any C/C++ refactoring tool based on libclang? (even simplest "toy example" ). In particular I do quote "...C++ is a bitch of a language to transform"
Halfway there: if a function uses a local name that hides the global name, the object file won't have an undefined symbol. nm can show you those undefined symbols, and then you know in which files you must replace at least some instances of that name.
However, you still have a problem in the rare cases that a file uses both the global name and in another function hides the global name. I'm not sure if this can be resolved with --ffunction-sections; but I think so: nm can show the section and thus you'll see the undefined symbols used in foo() appear in section .text.foo.
In case of developing a static lib using fortran:
The lib is consist of multiple modules, e.g. "module a", "module b" etc..
Each of the modules has public variables, types and procedures.
Now, want to use the lib in program "test".
One possible method is to use each of the modules, and providing the *.a lib file during linking. e.g.:
program test
use a
use b
...
end program
But it would be better if only one module/*.h needs to be used/included. e.g.:
program test
use all
...
end program
One possible solution is to copy all public variables, types and interface of procedures into "module all", and use "module all" instead of the individual modules.
But if any of the individual module is modified, "module all" also needs to be modified to meet the change.
Is there a more appropriate method to work around, or is there an automatic tool to generate the "module all"?
Thank you very much for any input.
I wouldn't copy code from the individual modules into module "all", because, as you say, that leads to extra work when code is changed. And possibility of error. Instead, "use" those modules in module "all". Then when you want them all you "use module all". When you want a particular module you use that one. What you have to guard against because it is forbidden is circular module references: A uses B uses C uses A is not allowed.
It seems that the ultimate solution is to use submodule, which unfortunately has not been supported by gcc.
See:
http://fortranwiki.org/fortran/show/Submodules
I have a huge template file and only few functions are used, and I want to isolate that part for test and comment the other half. How can i find what's the best way to do this ?
How can I do this on a Windows system and the template file is .hxx ?
I like Mohammad's answer. Oops... he removed it - but basically - use a tool like nm - I don't know a windows equivalent but there's sure to be one - to query the objects for instantations. While your templates may be in a .hxx, you can only meaningfully talk about the subset of methods instantiated by some body of client code. You may need to do this analysis with inlining disabled, to ensure the function bodies are actually instantiated in a tangible form in the object files.
In the less likely event that you might have instantiated stuff because some code handles cases that you know the data doesn't - and won't evolve to - use, then you may prefer automated run-time coverage analysis. Many compilers (e.g. GCC's g++ -ftest-coverage) and tools (e.g. purecov) provide this.
How about commenting out the whole file, then uncommenting individual methods when the linker complains, until the program can be compiled ?
By the way, if you are using Visual Studio, commenting the whole file is just a matter of using the following key shortcuts : Ctrl+A, then Ctrl+K+C. You can uncomment selected lines using Ctrl+K+U.