C++11: auto and decltype

auto_and_decltype.cpp

#include <iostream>
#include <string>
#include <vector>
#include <numeric>
#include <functional>
using namespace std;

template <typename T>
auto cube(T x) -> decltype(x)
{
    return x*x*x;
}

template <typename F, typename G, typename T>
auto compose(F f, G g) -> function<T(T)>
{
    return [=](T x){ return f(g(x)); };
}

int main()
{
    cout << "[1] using string" << endl;
    auto str = string("Hello, world!");
    cout << str << endl;

    cout << "[2] using vector" << endl;
    auto ary = vector<int>(4);
    iota(ary.begin(), ary.end(), 0);
    for (auto x : ary) {
        cout << x << endl;
    }

    cout << "[3] using lambda function" << endl;
    auto f = [](int x){ return x*x; };
    for (auto x : ary) {
        cout << f(x) << endl;
    }

    cout << "[4] using template function" << endl;
    auto g = cube<int>;
    for (auto x : ary) {
        cout << g(x) << endl;
    }
    auto G = cube<double>;
    cout << G(1.1) << endl;

    cout << "[5] using high-order function" << endl;
    auto h = compose<decltype(f), decltype(g), int>(f, g);
    for (auto x : ary) {
        cout << h(x) << endl;
    }
    auto GG = compose<decltype(G), decltype(G), double>(G, G);
    cout << GG(1.1) << endl;

    return 0;
}

gistfile1.txt

$ g++ --version
g++ (GCC) 4.8.2
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ g++ --std=c++11 -o auto_and_decltype auto_and_decltype.cpp

$ ./auto_and_decltype
[1] using string
Hello, world!
[2] using vector
0
1
2
3
[3] using lambda function
0
1
4
9
[4] using template function
0
1
8
27
1.331
[5] using high-order function
0
1
64
729
2.35795