尝试使用尾随返回类型和标签调度,我编写了以下代码。
#include <string>
#include <iostream>
using namespace std;
namespace Params
{
struct t_param1{};
struct t_param2{};
};
template<typename t_detail>
struct Select;
template<>
struct Select<Params::t_param1> {using choice = Params::t_param1;};
template<>
struct Select<Params::t_param2> {using choice = Params::t_param2;};
class Tester
{
private:
using t_uint32 = uint32_t;
using t_string = string;
private:
t_uint32 m_param1;
// t_string m_param2;
private:
template<typename t_entity>
void assign(const Params::t_param1&, t_entity&& entity);
template<typename t_entity>
void assign(const Params::t_param2&, t_entity&& entity);
auto access(const Params::t_param1&) -> decltype(m_param1);
// auto access(const Params::t_param2&) -> decltype(m_param2);
public:
template<typename t_detail, typename t_entity>
void assign(t_entity&& entity);
template<typename t_detail>
auto access() -> decltype(access(typename Select<t_detail>::choice()));
};
template<typename t_detail, typename t_entity>
void
Tester::assign(t_entity&& entity)
{
assign(typename Select<t_detail>::choice(), entity);
}
template<typename t_entity>
void
Tester::assign(const Params::t_param1&, t_entity&& entity)
{
m_param1 = entity;
cout << "Assigned m_param1 with " << entity << endl;
}
/*
template<typename t_entity>
void
Tester::assign(const Params::t_param2&, t_entity&& entity)
{
m_param2 = entity;
cout << "Assigned m_param2 with " << entity << endl;
}
*/
template<typename t_detail>
auto
Tester::access()
-> decltype(access(typename Select<t_detail>::choice()))
{
return(access(typename Select<t_detail>::choice()));
}
auto
Tester::access(const Params::t_param1&)
-> decltype(m_param1)
{
return(m_param1);
}
/*
auto
Tester::access(const Params::t_param2&)
-> decltype(m_param2)
{
return(m_param2);
}
*/
int main() {
auto tester = Tester();
tester.assign<Params::t_param1>(79);
// tester.assign<Params::t_param2>("viziv");
auto param1 = tester.access<Params::t_param1>();
// auto param2 = tester.access<Params::t_param2>();
cout << "Access: param1 = " << param1 << endl;
// cout << "Access: param2 = " << param2 << endl;
return 0;
}
当我使用 Apple LLVM 版本 7.0.2 (clang-700.1.81) 编译此代码时,出现以下编译错误
junk1.cpp:78:9: error: out-of-line definition of 'access' does not match any declaration in 'Tester'
Tester::access()
^~~~~~
1 error generated.
奇怪的是,当我取消注释分配和访问 param2 的代码(在上面的代码中注释掉)时,它编译得很好并产生了所需的结果。
我究竟做错了什么?谁能向我解释为什么在编译行为中包含 param2 更改?