lambda捕获支持varidiac模板参数 [英] Does lambda capture support varidiac template arguments
问题描述
这将是很好,如果我可以做以下:
模板< class RT,class ... PT&
class Event
{
...
void operator()(PT ... args)
{
std :: for_each b l.begin(),l.end(),[args ...](Handler * p){(* p)(args ...);}
);
}
...
};不幸的是我无法使用g ++ 4.7.2编译(-std = c ++ 0x) ):
evtempl.hh:在成员函数'void elt :: Event :: operator()(PT ...)':
evtempl.hh:75:54:error:expected','before'...'token
evtempl.hh:75:54:error: $ b evtempl.hh:75:57:error:参数包不用'...'扩展:
evtempl.hh:75:57:note:'args'
evtempl.hh:In lambda函数:
evtempl.hh:76:26:错误:扩展模式'args'不包含任何参数包
evtempl.hh:在'void elt :: Event :: operator() ..)[with RT = void; PT:{int}]':
testevtempl.cc:28:9:从这里需要
evtempl.hh:74:9:错误:使用无效字段'elt :: Event :: operator (PT ...)::::Handler *)> :: __ args'
evtempl.hh:在实例化'void elt :: Event :: operator()(PT ...) void; ':
testevtempl.cc:29:20:从这里需要
evtempl.hh:74:9:错误:使用无效字段'elt :: Event: :operator()(PT ...):::: Handler *)> :: __ args'
将lambda改为旧的,世俗的语法:
for(itr = l.begin(); itr!= l.end (); ++ itr)
(*(* itr))(args ...);
这个编译工作正常。
我不知道为什么lambda语法不起作用。
- 我做错了什么或错过了什么?
- 这种东西在c ++ 11标准中是否被禁止?
- 或者,这是标准允许的,但是当前编译器的
a问题?
我尝试过
[=](Handler * p){(* p)(args ...) ; }
它给出的错误与您所做的一样:
[args](Handler * p){(* p)(args ...); }
抱怨参数包未展开
解决方案这是gcc中的一个错误。请参见 [c ++ 0x] lambdas和可变参数模板不能同时使用或可能 [C ++ 11]包扩展在lambda表达式中失败。
It would be nice if I could do the following:
template <class RT, class... PT>
class Event
{
...
void operator()(PT... args)
{
std::for_each(
l.begin(), l.end(), [args...](Handler *p) { (*p)(args...); }
);
}
...
};
Unfortunately I couldn't make it compile with g++ 4.7.2 (-std=c++0x):
evtempl.hh: In member function 'void elt::Event::operator()(PT ...)':
evtempl.hh:75:54: error: expected ',' before '...' token
evtempl.hh:75:54: error: expected identifier before '...' token
evtempl.hh:75:57: error: parameter packs not expanded with '...':
evtempl.hh:75:57: note: 'args'
evtempl.hh: In lambda function:
evtempl.hh:76:26: error: expansion pattern 'args' contains no argument packs
evtempl.hh: In instantiation of 'void elt::Event::operator()(PT ...) [with RT = void; PT = {int}]':
testevtempl.cc:28:9: required from here
evtempl.hh:74:9: error: using invalid field 'elt::Event::operator()(PT ...)::::Handler*)>::__args'
evtempl.hh: In instantiation of 'void elt::Event::operator()(PT ...) [with RT = void; PT = {int, const char*}]':
testevtempl.cc:29:20: required from here
evtempl.hh:74:9: error: using invalid field 'elt::Event::operator()(PT ...)::::Handler*)>::__args'
instead, I have to change that lambda to the old, mundane syntax:
for (itr = l.begin(); itr != l.end(); ++itr)
(*(*itr))(args...);
This one compiles and works fine.
I wonder why the lambda syntax doesn't work.
- Did I do something wrong or miss something?
- Is such thing outlawed in the c++11 standard?
- or, this is allowed by the standard, but it's
a problem of the current compiler?
I tried
[=](Handler *p) { (*p)(args...); }
it gives the same error as if you did:
[args](Handler *p) { (*p)(args...); }
complaining parameter packs not expanded
解决方案 It's a bug in gcc. See [c++0x]lambdas and variadic templates don't work together or perhaps [C++11] Pack expansion fails in lambda expressions.
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