23.03.2023 
The familiar solution for thick value classes that want to preserve binary compatibility is to use the pimpl pattern (private implementation), also known as d-pointer (pointer to data). In future versions of our class, we can freely change the contents of the pimpl (i.e. adding, removing, and/or modifying data members) but the binary compatibility of […]
Author Archives: Giuseppe D'Angelo
FMA Woes
Floating-point math is hard, and compilers will exploit every language loophole to make our FP calculations go faster, sometimes with surprising results.
QObjects, Ownership, propagate_const and C++ Evolution Const Correctness in Qt Applications
A very common implementation pattern for QObject subclasses is to declare its child QObjects as data members of type “pointer to child.” Raise your hand No, keep your hand on your computer input device 🙂 Nod if you have ever seen code like this (and maybe even written code like this yourself): A fairly common […]
On QVarLengthArray and Uninitialized Storage in C++
If you’re following our Youtube channel you might have heard me talking about QVarLengthArray. If you’re not… you should follow us! But let me give you a quick recap. QVarLengthArray is a Qt container that acts like a vector; its elements are stored contiguously in memory and it has a dynamic size. At any time […]
C++23 Will Be Really Awesome (a blog for April Fools Day)
C++23 is feature complete and on track to be released next year. While many people are complaining that it’s, after all, a “minor” release (as the pandemic made the Committee work very difficult), C++23 still has a few very significant changes. In this blog post, I want to talk about what I think is my […]
KDFunctionalSortFilterProxyModel A Functional Sort/Filter Proxy Model
Another day, another small addition to KDToolBox, KDAB’s collection of miscellaneous useful C++ classes and stuff. In this post, we’re going to talk about KDFunctionalSortFilterProxyModel, which is a convenience subclass of QSortFilterProxyModel. What’s a proxy model to begin with, and what’s QSortFilterProxyModel? Well, that explanation requires a bigger space than what I have in this […]
On the Removal of toSet(), toList() and Others or "How Do I Convert a QList to QSet in Qt 6?"
(Apologies for the clickbait in the post title! But I’d really like people who are searching for solutions to read this.) Between Qt 5.14 and Qt 5.15, my colleague, Marc Mutz, and I submitted a series of patches to Qt that added “range constructors” to the Qt containers. This brought Qt containers one step closer […]
New in Qt 6.1: std::hash Support for QHash
In the previous blog post of this series, we discussed KDToolBox::QtHasher, a helper class that allows us to use unordered associative containers datatypes which have a qHash() overload but not a std::hash specialization. The majority of Qt value classes indeed are lacking such a specialization, even if they do provide a qHash() overload. For our […]
Single-Shot Signal/Slot Connections
Sometimes it’s useful to establish a connection between a signal and a slot that should be activated only once. This is not how signal/slot connections normally behave. Remember that, when a connection is established, it will stay active until: the connection is explicitly disconnected; or the sender object is destroyed; or the receiver object is […]
Signal/Slot Connection Throttlers
Another day, another blog post about KDToolBox, KDAB’s collection of miscellaneous useful C++ classes and stuff. Today, we’ll talk about ways to throttle your signal/slots connections — in other words, how to activate a slot less often than the emission rate of the signal it’s connected to. The usual reason why you may want something […]