C++ boost::static\u visitor中运算符()中的附加参数
我必须创建C++ boost::static\u visitor中运算符()中的附加参数,c++,performance,boost,c++14,variant,C++,Performance,Boost,C++14,Variant,我必须创建boost::variant对象并使用static\u visitor。 不幸的是,我需要额外的参数 什么解决方案更好? 要将此对象作为类的字段,并且当我要使用visitor时,我必须创建实例: class Visitor : public boost::static_visitor<> { public: Visitor(int extra): extra{extra} {} void operator()(const T1&) { /* ...
boost::variant
对象并使用static\u visitor
。
不幸的是,我需要额外的参数
什么解决方案更好?
要将此对象作为类的字段,并且当我要使用visitor时,我必须创建实例:
class Visitor : public boost::static_visitor<>
{
public:
Visitor(int extra): extra{extra} {}
void operator()(const T1&) { /* ... */}
void operator()(const T2&) { /* ... */}
private:
int extra;
};
或者一次性使用boost::bind和create Visitor并使用boost::bind
class Visitor : public boost::static_visitor<>
{
public:
void operator()(const T1&, int extra) { /* ... */ }
void operator()(const T2&, int extra) { /* ... */ }
};
什么是更好(更快、更优雅)的解决方案
或者有更好的解决方案吗?没有比这更优雅的方法了。您可以使用lambdas(如果您的编译器/boost版本足够现代)
“低技术”选项是使用保存状态的结构(第三个示例):
#include <boost/variant.hpp>
#include <iostream>
struct T1{};
struct T2{};
struct Visitor : boost::static_visitor<>
{
void operator()(T1 const&, int extra) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
void operator()(T2 const&, int extra) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
};
int main() {
boost::variant<T1, T2> tests[] = { T1{}, T2{} };
{
Visitor vis;
for (auto v: tests)
apply_visitor([=](auto const& v) { vis(v, 42); }, v);
}
{
auto vis = [vis=Visitor{}](auto const& v) { vis(v, 1); };
for (auto v: tests)
apply_visitor(vis, v);
}
{
struct {
using result_type = void;
int extra;
void operator()(T1 const&) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
void operator()(T2 const&) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
} vis { 99 };
for (auto v: tests)
apply_visitor(vis, v);
}
}
#包括
#包括
结构T1{};
结构T2{};
结构访问者:boost::static\u访问者
{
void运算符()(T1常量和,int额外)常量{std::cout
auto visitor = std::bind(SctpManager::Visitor(), std::placeholders::_1, extra);
boost::apply_visitor(visitor, t);
#include <boost/variant.hpp>
#include <iostream>
struct T1{};
struct T2{};
struct Visitor : boost::static_visitor<>
{
void operator()(T1 const&, int extra) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
void operator()(T2 const&, int extra) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
};
int main() {
boost::variant<T1, T2> tests[] = { T1{}, T2{} };
{
Visitor vis;
for (auto v: tests)
apply_visitor([=](auto const& v) { vis(v, 42); }, v);
}
{
auto vis = [vis=Visitor{}](auto const& v) { vis(v, 1); };
for (auto v: tests)
apply_visitor(vis, v);
}
{
struct {
using result_type = void;
int extra;
void operator()(T1 const&) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
void operator()(T2 const&) const { std::cout << __PRETTY_FUNCTION__ << " extra:" << extra << "\n"; }
} vis { 99 };
for (auto v: tests)
apply_visitor(vis, v);
}
}
void Visitor::operator()(const T1&, int) const extra:42
void Visitor::operator()(const T2&, int) const extra:42
void Visitor::operator()(const T1&, int) const extra:1
void Visitor::operator()(const T2&, int) const extra:1
void main()::<unnamed struct>::operator()(const T1&) const extra:99
void main()::<unnamed struct>::operator()(const T2&) const extra:99