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I love C++ programming language for its power and complexity!! To me, its enormity and complexity has been an incessant source of different features to understand. C++ is still evolving, therefore, I'll have new stuff to learn for quite a while. Many of the C++ features are quite exotic and thats why I am interested in them. On this blog you will find exotic C++ stuff such as core language features, idioms, patterns, C++ emerging standards etc. This is not a beginners blog. You will find here intermediate to advanced level material on C++. I also plan to put new C++ material as I learn it. You might find thoughts presented here already presented somewhere else like popular C++ books, magazines, e-zines, websites, blogs etc. This is becasue I learn from these popular sources. Site Feed URL: http://cpptruths.blogspot.com/atom.xml

WhoamI?
I am not a guru in C++. But I put serious efforts into learning anything remotely related to C++.
More about me: http://www.cs.nmsu.edu/~stambe

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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 two r…

Understanding Fold Expressions

C++17 has an interesting new feature called fold expressions. Fold expressions offer a compact syntax to apply a binary operation to the elements of a parameter pack. Here’s an example. template <typename... Args> auto addall(Args... args) { return (... + args); } addall(1,2,3,4,5); // returns 15. This particular example is a unary left fold. It's equivalent to ((((1+2)+3)+4)+5). It reduces/folds the parameter pack of integers into a single integer by applying the binary operator successively. It's unary because it does not explicitly specify an init (a.k.a. identity) argument. So, let add it. template <typename... Args> auto addall(Args... args) { return (0 + ... + args); } addall(1,2,3,4,5); // returns 15. This version of addall is a binary left fold. The init argument is 0 and it's redundant (in this case). That's because this fold expression is equivalent to (((((0+1)+2)+3)+4)+5). Explicit identity elements will come in handy a little la…

Folding Monadic Functions

In the previous two blog posts (Understanding Fold Expressions and Folding Functions) we looked at the basic usage of C++17 fold expressions and how simple functions can be folded to create a composite one. We’ll continue our stride and see how "embellished" functions may be composed in fold expressions.

First, let me define what I mean by embellished functions. Instead of just returning a simple value, these functions are going to return a generic container of the desired value. The choice of container is very broad but not arbitrary. There are some constraints on the container and once you select a generic container, all functions must return values of the same container. Let's begin with std::vector.
// Hide the allocator template argument of std::vector. // It causes problems and is irrelevant here. template <class T> struct Vector : std::vector<T> {}; struct Continent { }; struct Country { }; struct State { }; struct City { }; auto get_countries…