Skip to main content

linked list using std::pair (infinite regression)

Defining a node of a linked-list using std::pair sounds as simple as drinking a Starbucks's white chocolate mocha. But it really isn't. Give it a try! The constraint is to use std::pair's first or second as a pointer to the structure itself, like in any linked-list's node. As far as I know, it is impossible unless you resort to ugly casts from void pointers. The problem is actually quite well known and gives rise to something known as infinite regress, where the problem you want to solve reappears in the solution to the problem.

typedef std::pair<int, /* Pointer to this pair!! */ > Node;

The closest thing I could come up with is something like the one below.

struct Node : std::pair <int, Node *>
{};

Node n;
n.second = &n; // A cyclic linked-list.

Comments

Unknown said…
In C++0x:

template <typename T> using Node = std::pair<T, Node*>;
Logan Capaldo said…
How does this grab you?

template <class <typename A, typename B> T, typename First>
struct Mu2 {
T<First, Mu2<T, First>* > mu;
};

Mu2<std::pair, int> m;
m.mu.second = &m;


It's not exactly what you asked for, but it is arguably closer than the solution with inheritance.
Sumant said…
It almost gave me a neck sprain, but it works! I've reorganized and simplified it a little.

template <template <typename, typename> class T, typename First>
struct Mu2
{
T<First, Mu2* > mu;
};
Cool stuff, can you check out my C++ Code Samples too?

Popular Content

Want speed? Use constexpr meta-programming!

It's official: C++11 has two meta-programming languages embedded in it! One is based on templates and other one using constexpr . Templates have been extensively used for meta-programming in C++03. C++11 now gives you one more option of writing compile-time meta-programs using constexpr . The capabilities differ, however. The meta-programming language that uses templates was discovered accidently and since then countless techniques have been developed. It is a pure functional language which allows you to manipulate compile-time integral literals and types but not floating point literals. Most people find the syntax of template meta-programming quite abominable because meta-functions must be implemented as structures and nested typedefs. Compile-time performance is also a pain point for this language feature. The generalized constant expressions (constexpr for short) feature allows C++11 compiler to peek into the implementation of a function (even classes) and perform optimization...

Multi-dimensional arrays in C++11

What new can be said about multi-dimensional arrays in C++? As it turns out, quite a bit! With the advent of C++11, we get new standard library class std::array. We also get new language features, such as template aliases and variadic templates. So I'll talk about interesting ways in which they come together. It all started with a simple question of how to define a multi-dimensional std::array. It is a great example of deceptively simple things. Are the following the two arrays identical except that one is native and the other one is std::array? int native[3][4]; std::array<std::array<int, 3>, 4> arr; No! They are not. In fact, arr is more like an int[4][3]. Note the difference in the array subscripts. The native array is an array of 3 elements where every element is itself an array of 4 integers. 3 rows and 4 columns. If you want a std::array with the same layout, what you really need is: std::array<std::array<int, 4>, 3> arr; That's quite annoying for...

Rvalue references in constructor: when less is more

I've seen a recurring mistake made by well-versed C++03 programmers when they set out to use rvalue references for the first time. In fact, as it turns out, better you are at C++03, easier it is to fall in the trap of rvalue reference anti-pattern I'm gonna talk about. Consider the following C++03 class: class Book { public: Book(const std::string & title, const std::vector<std::string> & authors, const std::string & pub, size_t pub_day const std::string & pub_month, size_t pub_year) : _title(title), _authors(authors), _publisher(pub), _pub_day(pub_day), _pub_month(pub_month), _pub_year(pub_year) {} // .... // .... private: std::string _title; std::vector<std::string> _authors; std::string _publisher; size_t _pub_day; std::string _pub_month; size_t _pub_year; }; The Book class above is as dull as it can be. Now lets C++11'fy it!...