I have a project that tries to implement keyboard macro scripting with chaiscript. I am writing a class based on xlib to wrap the xlib code.
I have a member function to add a modifier key to an ignored list, because of a xlib quirk.
how could i do something like the following minimal example.
#include <chaiscript/chaiscript.hpp>
#include <functional>
class MacroEngine{
public:
MacroEngine() = default;
//...
void addIgnoredMod(int modifier){
ignoredMods |= modifier;
}
//...
private:
int ignoredMods;
};
int main(int argc, char *argv[]){
MacroEngine me;
chaiscript::ChaiScript chai;
//...
chai.add(chaiscript::fun(std::bind(&MacroEngine::addIgnoredMod, me, std::placeholders::_1)), "setIgnoredMods");
//...
return 0;
}
I tried bind and failed with the following error message:
In file included from ../deps/ChaiScript/include/chaiscript/dispatchkit/proxy_functions_detail.hpp:24:0,
from ../deps/ChaiScript/include/chaiscript/dispatchkit/proxy_functions.hpp:27,
from ../deps/ChaiScript/include/chaiscript/dispatchkit/proxy_constructors.hpp:14,
from ../deps/ChaiScript/include/chaiscript/dispatchkit/dispatchkit.hpp:34,
from ../deps/ChaiScript/include/chaiscript/chaiscript_basic.hpp:12,
from ../deps/ChaiScript/include/chaiscript/chaiscript.hpp:823,
from ../src/main.cpp:2:
../deps/ChaiScript/include/chaiscript/dispatchkit/callable_traits.hpp: In instantiation of ‘struct chaiscript::dispatch::detail::Callable_Traits<std::_Bind<void (MacroEngine::*(MacroEngine, std::_Placeholder<1>))(unsigned int)> >’:
../deps/ChaiScript/include/chaiscript/language/../dispatchkit/register_function.hpp:45:72: required from ‘chaiscript::Proxy_Function chaiscript::fun(const T&) [with T = std::_Bind<void (MacroEngine::*(MacroEngine, std::_Placeholder<1>))(unsigned int)>; chaiscript::Proxy_Function = std::shared_ptr<chaiscript::dispatch::Proxy_Function_Base>]’
../src/main.cpp:21:95: required from here
../deps/ChaiScript/include/chaiscript/dispatchkit/callable_traits.hpp:99:84: error: decltype cannot resolve address of overloaded function
typedef typename Function_Signature<decltype(&T::operator())>::Signature Signature;
^~~~~~~~~
../deps/ChaiScript/include/chaiscript/dispatchkit/callable_traits.hpp:100:86: error: decltype cannot resolve address of overloaded function
typedef typename Function_Signature<decltype(&T::operator())>::Return_Type Return_Type;
^~~~~~~~~~~
I also tried to make the variable static which worked, but it wont work if I try to make it possible to ignore modifiers on a per hotkey basis.
what am i doing wrong? and how can I fix it?
You can do this instead:
chai.add(chaiscript::fun(&MacroEngine::addIgnoredMod, &me), "addIgnoredMod");
Or use a lambda:
chai.add(chaiscript::fun([&me](int modifier){ me.addIgnoredMod(modifier); }), "addIgnoredMod");
Jason Turner, the creator of Chaiscript, commented on it here: http://discourse.chaiscript.com/t/may-i-use-std-bind/244/4
"There’s really never any good reason to use std::bind. I much better solution is to use a lambda (and by much better, I mean much much better. std::bind adds to compile size, compile time and runtime)."
Related
I'm using the pimpl-idiom with std::unique_ptr:
class window {
window(const rectangle& rect);
private:
class window_impl; // defined elsewhere
std::unique_ptr<window_impl> impl_; // won't compile
};
However, I get a compile error regarding the use of an incomplete type, on line 304 in <memory>:
Invalid application of 'sizeof' to an incomplete type 'uixx::window::window_impl'
For as far as I know, std::unique_ptr should be able to be used with an incomplete type. Is this a bug in libc++ or am I doing something wrong here?
Here are some examples of std::unique_ptr with incomplete types. The problem lies in destruction.
If you use pimpl with unique_ptr, you need to declare a destructor:
class foo
{
class impl;
std::unique_ptr<impl> impl_;
public:
foo(); // You may need a def. constructor to be defined elsewhere
~foo(); // Implement (with {}, or with = default;) where impl is complete
};
because otherwise the compiler generates a default one, and it needs a complete declaration of foo::impl for this.
If you have template constructors, then you're screwed, even if you don't construct the impl_ member:
template <typename T>
foo::foo(T bar)
{
// Here the compiler needs to know how to
// destroy impl_ in case an exception is
// thrown !
}
At namespace scope, using unique_ptr will not work either:
class impl;
std::unique_ptr<impl> impl_;
since the compiler must know here how to destroy this static duration object. A workaround is:
class impl;
struct ptr_impl : std::unique_ptr<impl>
{
~ptr_impl(); // Implement (empty body) elsewhere
} impl_;
As Alexandre C. mentioned, the problem comes down to window's destructor being implicitly defined in places where the type of window_impl is still incomplete. In addition to his solutions, another workaround that I've used is to declare a Deleter functor in the header:
// Foo.h
class FooImpl;
struct FooImplDeleter
{
void operator()(FooImpl *p);
};
class Foo
{
...
private:
std::unique_ptr<FooImpl, FooImplDeleter> impl_;
};
// Foo.cpp
...
void FooImplDeleter::operator()(FooImpl *p)
{
delete p;
}
Note that using a custom Deleter function precludes the use of std::make_unique (available from C++14), as already discussed here.
use a custom deleter
The problem is that unique_ptr<T> must call the destructor T::~T() in its own destructor, its move assignment operator, and unique_ptr::reset() member function (only). However, these must be called (implicitly or explicitly) in several PIMPL situations (already in the outer class's destructor and move assignment operator).
As already pointed out in another answer, one way to avoid that is to move all operations that require unique_ptr::~unique_ptr(), unique_ptr::operator=(unique_ptr&&), and unique_ptr::reset() into the source file where the pimpl helper class is actually defined.
However, this is rather inconvenient and defies the very point of the pimpl idoim to some degree. A much cleaner solution that avoids all that is to use a custom deleter and only move its definition into the source file where the pimple helper class lives. Here is a simple example:
// file.h
class foo
{
struct pimpl;
struct pimpl_deleter { void operator()(pimpl*) const; };
std::unique_ptr<pimpl,pimpl_deleter> m_pimpl;
public:
foo(some data);
foo(foo&&) = default; // no need to define this in file.cc
foo&operator=(foo&&) = default; // no need to define this in file.cc
//foo::~foo() auto-generated: no need to define this in file.cc
};
// file.cc
struct foo::pimpl
{
// lots of complicated code
};
void foo::pimpl_deleter::operator()(foo::pimpl*ptr) const { delete ptr; }
Instead of a separate deleter class, you can also use a free function or static member of foo:
class foo {
struct pimpl;
static void delete_pimpl(pimpl*);
using deleter = void(&)(pimpl*);
std::unique_ptr<pimpl,deleter> m_pimpl;
public:
foo(some data);
};
Probably you have some function bodies within .h file within class that uses incomplete type.
Make sure that within your .h for class window you have only function declaration. All function bodies for window must be in .cpp file. And for window_impl as well...
Btw, you have to explicitly add destructor declaration for windows class in your .h file.
But you CANNOT put empty dtor body in you header file:
class window {
virtual ~window() {};
}
Must be just a declaration:
class window {
virtual ~window();
}
To add to the other's replies about the custom deleter, in our internal "utilities library" I added a helper header to implement this common pattern (std::unique_ptr of an incomplete type, known only to some of the TU to e.g. avoid long compile times or to provide just an opaque handle to clients).
It provides the common scaffolding for this pattern: a custom deleter class that invokes an externally-defined deleter function, a type alias for a unique_ptr with this deleter class, and a macro to declare the deleter function in a TU that has a complete definition of the type. I think that this has some general usefulness, so here it is:
#ifndef CZU_UNIQUE_OPAQUE_HPP
#define CZU_UNIQUE_OPAQUE_HPP
#include <memory>
/**
Helper to define a `std::unique_ptr` that works just with a forward
declaration
The "regular" `std::unique_ptr<T>` requires the full definition of `T` to be
available, as it has to emit calls to `delete` in every TU that may use it.
A workaround to this problem is to have a `std::unique_ptr` with a custom
deleter, which is defined in a TU that knows the full definition of `T`.
This header standardizes and generalizes this trick. The usage is quite
simple:
- everywhere you would have used `std::unique_ptr<T>`, use
`czu::unique_opaque<T>`; it will work just fine with `T` being a forward
declaration;
- in a TU that knows the full definition of `T`, at top level invoke the
macro `CZU_DEFINE_OPAQUE_DELETER`; it will define the custom deleter used
by `czu::unique_opaque<T>`
*/
namespace czu {
template<typename T>
struct opaque_deleter {
void operator()(T *it) {
void opaque_deleter_hook(T *);
opaque_deleter_hook(it);
}
};
template<typename T>
using unique_opaque = std::unique_ptr<T, opaque_deleter<T>>;
}
/// Call at top level in a C++ file to enable type %T to be used in an %unique_opaque<T>
#define CZU_DEFINE_OPAQUE_DELETER(T) namespace czu { void opaque_deleter_hook(T *it) { delete it; } }
#endif
May be not a best solution, but sometimes you may use shared_ptr instead.
If course it's a bit an overkill, but... as for unique_ptr, I'll perhaps wait 10 years more until C++ standard makers will decide to use lambda as a deleter.
Another side.
Per your code it may happen, that on destruction stage window_impl will be incomplete. This could be a reason of undefined behaviour.
See this:
Why, really, deleting an incomplete type is undefined behaviour?
So, if possible I would define a very base object to all your objects, with virtual destructor. And you're almost good. You just should keep in mind that system will call virtual destructor for your pointer, so you should define it for every ancestor. You should also define base class in inheritance section as a virtual (see this for details).
Using extern template
The issue with using std::unique_ptr<T> where T is an incomplete type is that unique_ptr needs to be able to delete an instance of T for various operations. The class unique_ptr uses std::default_delete<T> to delete the instance. Hence, in an ideal world, we would just write
extern template class std::default_delete<T>;
to prevent std::default_delete<T> from being instantiated. Then, declaring
template class std::default_delete<T>;
at a place where T is complete, would instantiate the template.
The issue here is that default_delete actually defines inline methods that will not be instantiated. So, this idea does not work. We can, however, work around this problem.
First, let us define a deleter that does not inline the call operator.
/* --- opaque_ptr.hpp ------------------------------------------------------- */
#ifndef OPAQUE_PTR_HPP_
#define OPAQUE_PTR_HPP_
#include <memory>
template <typename T>
class opaque_delete {
public:
void operator() (T* ptr);
};
// Do not move this method into opaque_delete, or it will be inlined!
template <typename T>
void opaque_delete<T>::operator() (T* ptr) {
std::default_delete<T>()(ptr);
}
Furthermore, for ease of use, define a type opaque_ptr which combines unique_ptr with opaque_delete, and analogously to std::make_unique, we define make_opaque.
/* --- opaque_ptr.hpp cont. ------------------------------------------------- */
template <typename T>
using opaque_ptr = std::unique_ptr<T, opaque_delete<T>>;
template<typename T, typename... Args>
inline opaque_ptr<T> make_opaque(Args&&... args)
{
return opaque_ptr<T>(new T(std::forward<Args>(args)...));
}
#endif
The type opaque_delete can now be used with the extern template construction. Here is an example.
/* --- foo.hpp -------------------------------------------------------------- */
#ifndef FOO_HPP_
#define FOO_HPP_
#include "opaque_ptr.hpp"
class Foo {
public:
Foo(int n);
void print();
private:
struct Impl;
opaque_ptr<Impl> m_ptr;
};
// Do not instantiate opaque_delete.
extern template class opaque_delete<Foo::Impl>;
#endif
Since we prevent opaque_delete from being instantiated this code compiles without errors. To make the linker happy, we instantiate opaque_delete in our foo.cpp.
/* --- foo.cpp -------------------------------------------------------------- */
#include "foo.hpp"
#include <iostream>
struct Foo::Impl {
int n;
};
// Force instantiation of opaque_delete.
template class opaque_delete<Foo::Impl>;
The remaining methods could be implemented as follows.
/* --- foo.cpp cont. -------------------------------------------------------- */
Foo::Foo(int n)
: m_ptr(new Impl)
{
m_ptr->n = n;
}
void Foo::print() {
std::cout << "n = " << m_ptr->n << std::endl;
}
The advantage of this solution is that, once opaque_delete is defined, the required boilerplate code is rather small.
Here is a variadic template that prints parameters.
#include <string>
#include <iostream>
void Output() {
std::cout<<std::endl;
}
template<typename First, typename ... Strings>
void Output(First arg, const Strings&... rest) {
std::cout<<arg<<" ";
Output(rest...);
}
int main() {
Output("I","am","a","sentence");
Output("Let's","try",1,"or",2,"digits");
Output(); //<- I do not want this to compile, but it does.
return 0;
}
Is there a way to get this functionality without having the "no parameter" call work, and without having to write two functions every time?
You might want to keep the separation of the first and the rest of the parameters, you can use:
template<typename First, typename ... Rest>
void Output(First&& first, Rest&&... rest) {
std::cout << std::forward<First>(first);
int sink[]{(std::cout<<" "<<std::forward<Rest>(rest),0)... };
(void)sink; // silence "unused variable" warning
std::cout << std::endl;
}
Note that I used perfect forwarding to avoid copying any parameters. The above has the additional benefit to avoid recursion and therefore is likely to produce better (faster) code.
The way I wrote sink also guarantees that the expressions expanded from rest are evaluated left-to-right - which is important when compared to the naïve approach of just writing a helper function template<typename...Args>void sink(Args&&...){}.
Live example
Call the function from a forwarding type function and have a static_assert like this:
template <typename ... Args>
void forwarder(Args ... args) {
static_assert(sizeof...(args),"too small");
Output(args...);
}
As far as I see there are two questsions:
How to avoid Output() calls with no parameters.
Is there a simpler way to end the compile time recursion?
My solution to item 1 is as follows:
template<typename T>
void Output(const T & string) {
std::cout<<string<<std::endl;
}
template<typename First, typename ... Strings>
void Output(const First & arg, const Strings & ... rest) {
std::cout<<arg<<" ";
Output(rest...);
}
Basically, instead of ending the recursion when the template list is empty, I end it when it only contains one type. There is one difference between the above and the code from the question: if does not output any space after the last item. Instead it just outputs the newline.
For question number two see the answer by Daniel Frey above. I really liked this solution, although it took some time to grasp it (and I upvoted the answer). At the same time I find that it makes the code harder to read/understand and therefore harder to maintain. Currently I would not not use that solution in anything but small personal code snippets.
In the clang_complete.txt(the help file), it shows these in clang_complete-compl_kinds:
2.Completion kinds *clang_complete-compl_kinds*
Because libclang provides a lot of information about completion, there are
some additional kinds of completion along with standard ones (see >
:help complete-items for details):
'+' - constructor
'~' - destructor
'e' - enumerator constant
'a' - parameter ('a' from "argument") of a function, method or template
'u' - unknown or buildin type (int, float, ...)
'n' - namespace or its alias
'p' - template ('p' from "pattern")
the question are:
1. i cannot access the complete-items(no this file)
2. can someone tell me how to use the parameter '+' 'a' and so on.
3. or can you tell me how to show function parameters when ( is typed.
thanks!
(forgive my poor english)
It's been a long time, but i'll answer to help future visitors.
I don't fully understand your questions, but I'll answer the 3rd one. Clang complete only launches automatic suggestion/completion when writing '.', '->' or '::', but you can launch it manually.
I use it this way. In this source:
#include <iostream>
using namespace std;
void ExampleFunc (float foo, int &bar)
{
cout << foo;
bar++;
}
int main (int argc, char **argv)
{
int a(0);
Exa[cursor here]
return 0;
}
Writing "Exa" you can press <C-X><C-U> and you will get a preview window with:
Example (float foo, int &bar)
and a completion window (the same that appears when you press <C-N> (CTRL-N) in insert mode) with:
Example f void Example(float foo, int &bar)
If there are several matches, you can move down or up with <C-N> or <C-P> and complete with <CR> (enter).
The completion is not perfect, but it should work for many other cases, for example (as you mentioned) templates:
#include <vector>
using namespace std;
int main (int argc, char **argv)
{
struct MyType {int asdf; float qwer;};
vector<MyType> vec;
ve // suggestions after <C-X><C-U>:
// "vec v vector<MyType> vec" v is for variable
// "vector p vector<Typename _Tp>" p is for pattern (template)
// constructors with its parameters, etc.
vec. // auto-fired suggestions: all std::vector methods
vec[0]. // auto-fired suggestions: "asdf", "qwer" and MyType methods
return 0;
}
If those examples don't work for you, you haven't installed the plugin properly.
By the way, you can map <C-X><C-U> to other shortcut.
I have this class defined in Global.h
class Global
{
public:
static string InttoStr(int num);
};
In Global.cpp, i have
Global::InttoStr(int num)
{
//Code To convert integer into string.
}
Now, from SubMove.cpp, when i call Global::InttoStr(num) I get following error:
error LNK2019: unresolved external symbol Global::InttoStr(int) referenced in function SubMove::toString(void)
Then I made the function non-static and called it like so:
Global g;
g.InttoStr(num);
But the error still persists.
I thought it had something to do with extern and searched it but i could not make any connection. Please help.
First off, try this:
string Global::InttoStr(int num)
{
//Code To convert integer into string.
}
Also, are you calling InttoStr from another library ? If so, you'll need to export the class "Global".
Best practice is to use a lib header (in the example below replace LIB_ with the name of the library):
#ifndef SOME_LIB_HEADER
#define SOME_LIB_HEADER
#if defined (LIB_EXPORTS)
#define LIB_API __declspec(dllexport)
#else
#define LIB_API __declspec(dllimport)
#endif // SOME_LIB_HEADER
Define LIB_EXPORTS in your project contianing Global, include the lib header in Global.h, then define the class like this
class LIB_API Global
{
// some code for the class definition
};
Each project should have its own LIB_EXPORTS and LIB_API definition like DLL1_EXPORTS, DLL1_API, DLL2_EXPORTS, DLL2_API etc.
Basically this makes a separate lib treat the previous dll with __declspec(dllimport) and resolve all externs.
After Cython's "Hello World" and the example of calling a function in the C math libraries here, what I really want to do is to have C code of my own in a separate file and use it from Cython. Following this, I modify the setup.py file:
sourcefiles = ['hello2_caller.pyx', 'hello2.c']
This is hello2.c (main is just there to compile and test it separately---though that product isn't present for the test:
#import <stdio.h>
void f() {
printf("%s", "Hello world!\n");
}
int main(int argc, const char* argv[]) {
f();
return 0;
}
This is hello2_caller.pyx
cdef extern from "hello2.c":
void f()
cpdef myf():
f()
I get:
In file included from hello2_caller.c:219:
hello2.c:3: warning: function declaration isn’t a prototype
So I guess I'm failing to provide a header in some way.. though just feeding setup.py a standard header like 'hello2.h' doesn't work. Can you point me to a working example or explain what I'm doing wrong. Thanks.
Thanks to help from the Cython users' list here.
My writeup here.
Bottom line: this is only a warning, that is not fixed by a declaration of f(), but the compiled .so works. I'm still not sure how you would provide a .h file to Cython or if there is a better way to do this.
And there's a couple of errors: should be #include, and don't list the .c file in sourcfiles.