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Showing posts from October, 2013

Creating Recursive Lambdas ... and returning them too!

Ever since C++ adopted lambda expressions, many have stumbled upon the question whether they can be recursive. IMO, if an anonymous function needs to call itself why not create a named function/functor in the first place? But I'm not here today to argue whether it is a good or bad design. So here it is: the most common way to create a recursive lambda in C++11. void test() { std::function<int(int)> fib = [&fib](int n) { return (n <= 2)? 1 : fib(n-1) + fib(n-2); }; } The way it works is quite interesting. First, I created a std::function object, fib, and captured that in the lambda by reference. When the lambda captures fib, it is uninitialized because nothing has been assigned to it yet. The compiler knows the type of fib so it does not complain. It happily creates a closure with an uninitialized std::function. Right after that, it assigns the closure to the fib object so it gets initialized. Therefore, the reference inside lambda also works automatical

Moving elements from STL containers and std::initializer_list

Lot has been said about effectively using move-semantics, such as return-by-value and pass sink arguments by-value to constructors (and move later). Dust seems to be settling on those issues because I see some evidence building up to support that. Not much has been said (I think) about using move-semantics for a collection of objects, however. I mean moving objects from one type of STL container to another and also moving elements from std::initializer_list. Moving STL Containers of the same type This one is simple. STL containers provide the necessary move operations: move-constructor and move-assign operator. So moving an entire vector<T> to another is pretty straight forward. But that is only one of several ways to construct a vector<T>. How about move constructing a std::vector from a vector with custom allocators? Or for that matter, from a std::list or a std::set? Moving objects from one type of STL container to another The classic way of copying object

Overloading in Overdrive: A Generic Data-Centric Messaging Library for DDS

Slides of my Silicon Valley Code Camp (2013) talk are now available . If you attended this session in person please evaluate it. I take feedback/comments seriously! Overloading in Overdrive: A Generic Data-Centric Messaging Library for DDS from Sumant Tambe Abstract: When it comes to sending data across a network, applications send either binary or self-describing data (XML). Both approaches have merits. Data Distribution Service (DDS) combines the best of both in what’s called “data-centric messaging”. DDS shares the type description once, upfront, and later on sends binary data that meets the type description. You typically use IDL or XSD to specify the types and run them through a code generator for type-safe wrapper APIs for your application in your programming language. Simple and fast! As it turns out, however, C++11 bends the rules once again. In this presentation you will learn about a template-based C++11 messaging library that gives the DDS code generator a run f