The generic from user1095108

Why mark delegate.h as obsolete

Hi, this is not a real issue.

I've been following your library since before you moved it to Github. I was wondering why you moved the delegate class to be obsolete?

Cheers

gnr::forwarder with std::bind -- static_assert(std::is_trivially_copyable<functor_type> ?

Hi,

Currently gnr::forwarder cannot take a std::bind object, since the following static_assert static_assert(std::is_trivially_copyable<functor_type>{},"" (ref) will issue an error.

Question: is that static_assert needed?
Thanks.

Details:
If you try the following code
https://github.com/user706/code_generic/blob/master/code/intern/forwarder_ex2.cpp
building as follows:

cd /tmp
git clone https://github.com/user706/code_generic
cd                                   code_generic
mkdir -p build
cd       build
cmake ..       # need at least cmake 3.8.2, which understands CMAKE_CXX_STANDARD of 17 https://cmake.org/cmake/help/v3.8/prop_tgt/CXX_STANDARD.html#prop_tgt:CXX_STANDARD
make -j8
./code/intern/forwarder_ex2

and then change the following snippet https://github.com/user706/code_generic/blob/master/code/intern/forwarder_ex2.cpp#L7
to use gnr::forwarder, as follows

// uncomment _one_ of the two lines below
//template <typename T, std::size_t N = 0> using FF = std::function<T>;
template <typename T, std::size_t N = default_size> using FF = gnr::forwarder<T, N>;  // this only works if commenting out lines with std::bind below, or changing forwarder.hpp

then you'll find that a rebuild with make will fail as follows

In file included from /tmp/code_generic/code/intern/forwarder_ex2.cpp:2:0:
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp: In instantiation of ‘void gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<void (*(int))(int)>; R = void; A = {}; long unsigned int N = 32ul; bool NE = false]’:
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:77:11:   required from ‘gnr::forwarder<R(A ...), N, NE>::forwarder(F&&) [with F = std::_Bind<void (*(int))(int)>; <template-parameter-2-2> = void; R = void; A = {}; long unsigned int N = 32ul; bool NE = false]’
/tmp/code_generic/code/intern/forwarder_ex2.cpp:46:60:   required from here
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:123:5: error: static assertion failed: functor not trivially copyable
     static_assert(std::is_trivially_copyable<functor_type>{},
     ^~~~~~~~~~~~~
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:128:11: error: cannot convert ‘gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<void (*(int))(int)>; R = void; A = {}; long unsigned int N = 32ul; bool NE = false]::<lambda(void*)>’ to ‘void (*)(void*)’ in assignment
     stub_ = [](void* const ptr, A&&... args) noexcept(noexcept(NE)) -> R
            
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp: In instantiation of ‘void gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(Foo, std::_Placeholder<1>)>; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]’:
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:77:11:   required from ‘gnr::forwarder<R(A ...), N, NE>::forwarder(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(Foo, std::_Placeholder<1>)>; <template-parameter-2-2> = void; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]’
/tmp/code_generic/code/intern/forwarder_ex2.cpp:61:72:   required from here
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:123:5: error: static assertion failed: functor not trivially copyable
     static_assert(std::is_trivially_copyable<functor_type>{},
     ^~~~~~~~~~~~~
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:128:11: error: cannot convert ‘gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(Foo, std::_Placeholder<1>)>; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]::<lambda(void*, int&&)>’ to ‘void (*)(void*, int&&)’ in assignment
     stub_ = [](void* const ptr, A&&... args) noexcept(noexcept(NE)) -> R
            
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp: In instantiation of ‘void gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(const Foo*, std::_Placeholder<1>)>; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]’:
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:77:11:   required from ‘gnr::forwarder<R(A ...), N, NE>::forwarder(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(const Foo*, std::_Placeholder<1>)>; <template-parameter-2-2> = void; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]’
/tmp/code_generic/code/intern/forwarder_ex2.cpp:65:73:   required from here
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:123:5: error: static assertion failed: functor not trivially copyable
     static_assert(std::is_trivially_copyable<functor_type>{},
     ^~~~~~~~~~~~~
/tmp/code_generic/code/extern/generic_cmake/generic/forwarder.hpp:128:11: error: cannot convert ‘gnr::forwarder<R(A ...), N, NE>::assign(F&&) [with F = std::_Bind<std::_Mem_fn<void (Foo::*)(int) const>(const Foo*, std::_Placeholder<1>)>; R = void; A = {int}; long unsigned int N = 32ul; bool NE = false]::<lambda(void*, int&&)>’ to ‘void (*)(void*, int&&)’ in assignment
     stub_ = [](void* const ptr, A&&... args) noexcept(noexcept(NE)) -> R
            
code/intern/CMakeFiles/forwarder_ex2.dir/build.make:62: recipe for target 'code/intern/CMakeFiles/forwarder_ex2.dir/forwarder_ex2.cpp.o' failed
make[2]: *** [code/intern/CMakeFiles/forwarder_ex2.dir/forwarder_ex2.cpp.o] Error 1
CMakeFiles/Makefile2:186: recipe for target 'code/intern/CMakeFiles/forwarder_ex2.dir/all' failed
make[1]: *** [code/intern/CMakeFiles/forwarder_ex2.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

The offending lines, are the ones using std::bind --- here, here and here.

However if one removes the following static_assert

    static_assert(std::is_trivially_copyable<functor_type>{},
      "functor not trivially copyable");

from code/extern/generic_cmake/generic/forwarder.hpp (ref), then it will compile.

Question: is that static_assert needed?
Thanks.

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