模板元编程

现代模板元编程 - 第一部分 - Cppcon 2014 - Walter E. Brown

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#include<stdio.h>

// example 1
template<unsigned M, unsigned N>
struct gcd
{
    static int const value = gcd<N, M % N>::value;
};

template<unsigned M>
struct gcd<M, 0> 
{   
    static_assert(M != 0);
    static int const value = M;
};

// example 2
template<class T>
struct rank
{
    static size_t const value = 0u;
};

template<class U, size_t N>
struct rank<U[N]>
{
    static size_t const value = 1u + rank<U>::value;
};

// example 3

template<class T>
struct remove_const
{
    using type = T;
};

template<class U>
struct remove_const<U const>
{
    using type = U;
};

// example 4
template<class T>
struct type_is
{
    using type = T;
};

template<class T>
struct remove_volatile : type_is<T> {};


template<class U>
struct remove_volatile<U volatile> : type_is<U> {};

// example 5

// primary template
template<bool, class T,class>
struct  IF : type_is<T> {};

// spetialization
template<class T, class F>
struct IF<false, T, F> : type_is<F> {};


int main(){
    printf("%d\n", gcd<666,324>::value);


    using array_t = int[10][20][30];
    printf("%ld\n", rank<array_t>::value);


    remove_const<int const>::type t;
    // remove_const_t<int const> t; // in c++14
}