STL-pair-like triplet class - do I roll my own?

问题

I want to use a triplet class, as similar as possible to std::pair. STL doesn't seem to have one. I don't want to use something too heavy, like Boost. Is there some useful FOSS non-restrictive-license triplet class I could lift from somewhere? Should I roll my own? Should I do something else entirely?

Edit: About std::tuple...

Is there really no benefit to a triplet-specific class? I mean, with tuple, I can't do

template<typename T1, typename T2, typename T3> std::tuple<T1, T2, T3> triple;

now can I? Won't I have to typedef individual-type-combination triples?

回答1:

No, don't roll your own. Instead, take a look at std::tuple - it's a generalization of std::pair. So here's a value-initialized triple of ints:

std::tuple<int, int, int> triple;

If you want, you can have a type alias for triples only:

template<typename T1, typename T2, typename T3>
using triple = std::tuple<T1, T2, T3>;

回答2:

If you can use C++11, use std::tuple

If not, use boost::tuple

回答3:

If you're using C++11, you can use std::tuple.

If you're using C++03, then you'll either need to resort to rolling your own (which isn't too hard), or using tuple from Boost.

回答4:

I think you need something like this:

template<typename T>
struct triplet
{
    T first, middle, last;
};

template<typename T>
triplet<T> make_triplet(const T &m1, const T &m2, const T &m3) 
{
    triplet<T> ans;
    ans.first = m1;
    ans.middle = m2;
    ans.last = m3;
    return ans;
}

Examples of usage:

triplet<double> aaa;
aaa = make_triplet<double>(1.,2.,3.);
cout << aaa.first << " " << aaa.middle << " "  << aaa.last << endl;

triplet<bool> bbb = make_triplet<bool>(false,true,false);
cout << bbb.first << " " << bbb.middle << " "  << bbb.last << endl;

I'm using this and it is enough for my purposes... If you want different types, though, just do some modifications:

template<typename T1, typename T2, typename T3>
struct triplet
{
    T1 first; 
    T2 middle;
    T3 last;
};

template<typename T1, typename T2, typename T3>
triplet<T1,T2,T3> make_triplet(const T1 &m1, const T2 &m2, const T3 &m3) 
{
    triplet<T1,T2,T3> ans;
    ans.first = m1;
    ans.middle = m2;
    ans.last = m3;
    return ans;
}

And the usage will be very similar:

triplet<bool,string,myDouble> ccc;
ccc = make_triplet<bool,string,double>(false,"AB",3.1415);
ccc.middle = "PI";
cout << ccc.first << " " << ccc.middle << " "  << ccc.last << endl;

回答5:

To add the aspect of similarity to std::pair, you could define a class that has first, second and third. My guess is that in In that case you cannot avoid making a subclass of std::pair and add a 'third' member. It's a few lines of code.

Furthermore, if you often use these things with the same type, you could make twins and triplet classes as well. Easily made with C++-11's 'using', like:

template <typename T> using twins = std::pair<T,T>;

来源：https://stackoverflow.com/questions/20705702/stl-pair-like-triplet-class-do-i-roll-my-own

标签

c++

c++-standard-library

stdtuple

triplet