您有多态函子(Foo 和 Bar)。
您想要为一组特定的操作数类型键入擦除它们。我建议为此目的定义一个类型擦除的函子类型:
struct ErasedFunctor
{
template<typename F> ErasedFunctor(F&& f)
: pimpl(new impl_<F>(std::forward<F>(f))) {}
template <typename T>
void operator()(T& oper) const {
assert(pimpl);
pimpl->call(oper);
}
private:
typedef boost::variant<int32_t&, int64_t&, double&, float&> Operand;
struct base_ { virtual void call(Operand oper) const = 0; };
// struct impl_ : base_ ...
std::shared_ptr<base_> pimpl;
};
现在您可以简单地将函数对象直接存储在映射中:
typedef std::map<std::string, ErasedFunctor> test_map;
test_map createFunMap() {
return test_map {
{ "foo", Foo<double>(1.0) },
{ "bar", Bar<int32_t>(1) },
};
}
让我们使用at("foo")
代替["foo"]
以避免必须使ErasedFunctor
默认可构造:
int main() {
test_map myMap = createFunMap();
double t = 5.0;
std::cout << t << std::endl;
myMap.at("foo")(t);
std::cout << t << std::endl;
myMap.at("bar")(t);
std::cout << t << std::endl;
}
Prints
5
void ErasedFunctor::apply::operator()(const F&, T&) const [with F = Foo<double>; T = double](5)
5
6
void ErasedFunctor::apply::operator()(const F&, T&) const [with F = Bar<int>; T = double](6)
6
5
See it 住在科里鲁 http://coliru.stacked-crooked.com/a/2771244b1fb13e24
更多背景请参见:
- 生成没有虚拟功能的接口? https://stackoverflow.com/questions/18859699/generating-an-interface-without-virtual-functions/18859931#18859931
完整样本
#include <boost/bind.hpp>
#include <boost/variant.hpp>
#include <iostream>
template <typename FooType> struct Foo {
const FooType tmp_value;
Foo(const FooType &tmp_) : tmp_value(tmp_) {}
template <typename Object> void operator()(Object &operand) const {
std::cout << operand << std::endl;
operand += tmp_value;
}
};
template <typename BarType> struct Bar {
const BarType tmp_value;
Bar(const BarType &tmp_) : tmp_value(tmp_) {}
template <typename Object> void operator()(Object &operand) const {
std::cout << operand << std::endl;
operand -= tmp_value;
}
};
struct ErasedFunctor
{
template<typename F> ErasedFunctor(F&& f)
: pimpl(new impl_<F>(std::forward<F>(f))) {}
template <typename T>
void operator()(T& oper) const {
assert(pimpl);
pimpl->call(oper);
}
private:
typedef boost::variant<int32_t&, int64_t&, double&, float&> Operand;
struct base_ { virtual void call(Operand oper) const = 0; };
struct apply : boost::static_visitor<void> {
template <typename F, typename T> void operator()(F const& f, T& v) const {
std::cout << __PRETTY_FUNCTION__ << "(" << v << ")\n";
f(v);
}
};
template <typename F> struct impl_ : base_ {
F f_;
impl_(F&& f) : f_(std::forward<F>(f)) { }
virtual void call(Operand oper) const override {
boost::apply_visitor(boost::bind(apply(), boost::cref(f_), _1), oper);
}
};
std::shared_ptr<base_> pimpl;
};
#include <map>
typedef std::map<std::string, ErasedFunctor> test_map;
test_map createFunMap() {
return test_map {
{ "foo", Foo<double>(1.0) },
{ "bar", Bar<int32_t>(1) },
};
}
int main() {
test_map myMap = createFunMap();
double t = 5.0;
std::cout << t << std::endl;
myMap.at("foo")(t);
std::cout << t << std::endl;
myMap.at("bar")(t);
std::cout << t << std::endl;
}