由于在看 QT5.15.2中的 connect方法中的 typedef QtPrivate::FunctionPointer<func1> SignalType;</func1>使用以及， QtPrivate::FunctionPointer的声明。而产生的疑问，因此有了这篇内容。 QtPrivate::FunctionPointer的声明如下：
template<typename Func> struct FunctionPointer { enum {ArgumentCount = -1, IsPointerToMemberFunction = false}; };
template<class Obj, typename Ret, typename... Args> struct FunctionPointer<Ret (Obj::*) (Args...)>
{
typedef Obj Object;
typedef List<Args...> Arguments;
typedef Ret ReturnType;
typedef Ret (Obj::*Function) (Args...);
enum {ArgumentCount = sizeof...(Args), IsPointerToMemberFunction = true};
template <typename SignalArgs, typename R>
static void call(Function f, Obj *o, void **arg) {
FunctorCall<typename Indexes<ArgumentCount>::Value, SignalArgs, R, Function>::call(f, o, arg);
}
};
QtPrivate::FunctionPointer的声明总共有七个，这里不再一一粘贴，看到这里不知诸位会不会产生以下几个疑问：
我这里使用的环境是 VS2019编写的代码， C++ 14的编译标准
到这里我想最初的那三个问题，小伙伴们应该已经知道答案了吧。问题如下：
根据 typedef List<args...> Arguments;</args...>衍生的验证， List模板类型的声明如下：
template <typename...> struct List { int primary; };
template <typename Head, typename... Tail> struct List<Head, Tail...> { typedef Head Car; typedef List<Tail...> Cdr; int ts; };
2.1 其他的几种写法
特化写法如下：
template <typename A, typename B> struct templateSpecialization {};
template <typename A> struct templateSpecialization<A, int> {};
template <> struct templateSpecialization<char, int> {};
#include
using namespace std;
class MyClass
{
public:
MyClass() = default;
~MyClass() = default;
void test(int,int) { return; }
};
template <typename A, typename B> struct templateSpecialization {};
template <typename A> struct templateSpecialization<A, int> {};
template <> struct templateSpecialization<char, int> {};
template <typename...> struct List { int primary; };
template <typename Head, typename... Tail> struct List<Head, Tail...> { typedef Head Car; typedef List<Tail...> Cdr; int ts; };
template <typename A, typename...> struct List2 { int primary; };
template <typename A, typename B,typename... Tail> struct List2<A, B,Tail...> { int abtail; };
template <typename A> struct List2<A> { int A; };
template <typename A, typename B> struct List2<A,B> { int AB; };
template <typename A, typename B, typename C> struct List2<A,B,C> { int ABC; };
template <typename A> struct Test { int primary; };
template <class A, typename... B> struct Test<A(*) (B...)> { int testAmultiB; };
template<class Obj> struct FunctionPointer {};
template<class Obj, typename Ret, typename... Args> struct FunctionPointer<Ret(Obj::*) (Args...)>
{
typedef Obj Object;
enum { ArgumentCount = sizeof...(Args), IsPointerToMemberFunction = true };
typedef List<Args...> Arguments;
};
template <typename Func1, typename Func2>
static inline void connect(const typename FunctionPointer<Func1>::Object* sender, Func1 signal,
const typename FunctionPointer<Func2>::Object* receiver, Func2 slot)
{
const type_info& nInfo = typeid(Func1);
cout << nInfo.name() << " | " << nInfo.raw_name() << " | " << nInfo.hash_code() << endl;
const type_info& inInfo = typeid(FunctionPointer<Func1>::Arguments::Car);
cout << inInfo.name() << " | " << inInfo.raw_name() << " | " << inInfo.hash_code() << endl;
cout << FunctionPointer<Func1>::ArgumentCount << endl;
}
int main()
{
typedef void (*ptr)();
Test<ptr> test1;
test1.testAmultiB;
FunctionPointer<void(MyClass::*)()> fpTest;
List<int,string> list1;
list1.ts = 0;
List<int> list2;
list2.ts = 0;
List<> list3;
list3.primary = 0;
List<int, string,int> list4;
list4.ts = 0;
List2<int> list21;
list21.A = 0;
List2<int,int> list22;
list22.AB = 0;
List2<int,int,int> list23;
list23.ABC;
MyClass a;
connect(&a, &MyClass::test, &a, &MyClass::test);
}
Original: https://blog.csdn.net/weixin_41111116/article/details/127821651
Author: 愤怒的小黄鸭
Title: C++类模板的重载
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