用vs2002实现tupe/Cons，以及对应的make，at，size，for_each操作
全特化，偏特化
https://harttle.land/2015/10/03/cpp-template.html
不支持偏特化的编译器的实现技巧
vs2002不支持偏特化，经过研究可以用struct内部包含的struct实现
比如,支持偏特化的编译器这样写
template <size_t N, class Cons>
struct At
{
};
而vs2002需要这样写
template <size_t N>
struct At
{
template <class Cons>
struct inner{};
};
全部代码如下
// testtuple.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
struct null_type{};
template <class T1, class T2 = null_type, class T3 = null_type, class T4 = null_type, class T5 = null_type>
struct tuple
{
T1 t1;
T2 t2;
T3 t3;
T4 t4;
T5 t5;
tuple(T1 t1_):t1(t1_)
{}
tuple(T1 t1_, T2 t2_):t1(t1_), t2(t2_)
{}
};
template <class T1, class T2 , class T3 , class T4 , class T5, class F>
void for_each(tuple<T1, T2, T3, T4, T5> &t, F f)
{
f(t.t1);
f(t.t2);
f(t.t3);
f(t.t4);
f(t.t5);
}
template <class Head= null_type, class Tail = null_type>
struct cons
{
typedef cons self_type;
typedef Head head_type;
typedef Tail tail_type;
Head head_;
Tail tail_;
cons(Head const &h, Tail const &t = Tail()):head_(h), tail_(t)
{}
};
template <class Head, class Tail>
cons<Head, Tail> make_cons(Head const &h, Tail const &t){
return cons<Head, Tail>(h, t);
}
template <class Head>
cons<Head> make_cons(Head const &h){
return cons<Head>(h);
}
template <size_t N>
struct At
{
template <class Cons>
struct inner
{
typedef typename At<N-1>::template inner<Cons::tail_type>::RET RET;
static RET &data(Cons &c) {
return At<N-1>::inner<Cons::tail_type>::data(c.tail_);
}
};
};
template <>
struct At<0>
{
template <class Cons>
struct inner
{
typedef typename Cons::head_type RET;
static RET &data(Cons &c) {
return c.head_;
}
};
};
template <class Cons>
struct Size
{
static const enum {value = 1 + Size<Cons::tail_type>::value };
};
template <>
struct Size <null_type>
{
static const enum {value = 0 };
};
template <>
struct Size <cons<> >
{
static const enum {value = 0 };
};
template <class Cons>
size_t size(Cons const &c)
{
return Size<Cons>::value;
}
template <class Cons>
struct ForEach
{
template <class F>
static void dof(Cons c, F f)
{
f(c.head_);
ForEach<Cons::tail_type>::dof(c.tail_, f);
}
};
template <>
struct ForEach<null_type>
{
template <class F>
static void dof(null_type c, F f)
{
}
};
template <>
struct ForEach<cons<> >
{
template <class F>
static void dof(cons<> c, F f)
{
}
};
template <class Cons, class F>
void for_each_cons(Cons c, F f)
{
ForEach<Cons>::dof(c, f);
}
struct Iter
{
void operator()(int v) const
{
std::cout << v << std::endl;
}
void operator()(null_type v) const
{}
};
int _tmain(int argc, _TCHAR* argv[])
{
tuple<int, int> t(1,2);
for_each(t, Iter());
std::cout << "----------------" << std::endl;
cons<int, cons<int> > c= make_cons(3, make_cons(2));
for_each_cons(c, Iter());
std::cout << "----------------" << std::endl;
At<1>::inner<cons<int, cons<int> > >::data(c) = 100;
size(c);
return 0;
}