C ++ make_shared不可用 [英] C++ make_shared not available
问题描述
虽然我在编译器中有 std :: tr1 :: shared_ptr< T>
,但我不
有 make_shared c>。
While I have std::tr1::shared_ptr<T>
available in my compiler, I don't
have make_shared
.
有人可以指示我正确实施 make_shared
吗?我看到
,我需要使用varargs为T的构造函数提供参数。
Can someone point me to a proper implementation of make_shared
? I see
that I need to use varargs to provide arguments to constructor of T.
但我没有可变参数模板在我的编译器也可用。
But I don't have variadic templates available in my compiler as well.
推荐答案
如果你的编译器没有给出make_shared的实现,你不能使用boost,缺少对对象和引用计数器的单分配优化然后make_shared是这样的:
If your compiler don't give an implementation of make_shared and you can't use boost, and you don't mind the lack of single-allocation optimization both for the object and the reference counter then make_shared is something like this:
没有可变模板支持:
// zero arguments version
template <typename T>
inline shared_ptr<T> make_shared()
{
return shared_ptr<T>(new T());
}
// one argument version
template <typename T, typename Arg1>
inline shared_ptr<T> make_shared(Arg1&& arg1)
{
return shared_ptr<T>(new T(std::forward<Arg1>(arg1)));
}
// two arguments version
template <typename T, typename Arg1, typename Arg2>
inline shared_ptr<T> make_shared(Arg1&& arg1, Arg2&& arg2)
{
return shared_ptr<T>(new T(std::forward<Arg1>(arg1),
std::forward<Arg2>(arg2)));
}
// ...
不支持r值引用,则为每个参数计数生成2个版本:一个 const Arg& 和一个 arg&
If your compiler don't support r-value references, then make 2 versions for each arguments count: one const Arg& and one Arg&
使用可变参数模板支持:
template <typename T, typename... Args>
inline shared_ptr<T> make_shared(Args&&... args)
{
return shared_ptr<T>(new T( std::forward<Args>(args)... ));
}
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