Move semantics and default constructors - Rule of Six?

A really long time ago - over four weeks! - I wrote about move safety.

I really need to force myself into blogging on a schedule. Let’s say I’ll publish something at least every two weeks.

The post spawned a lot of discussion about whether you should rely on moved-from state behavior or make any guarantees. See the first half of this CppChat episode for more.

BTW: Thanks for the nice words, Jon! Really appreciate it.

But I’m not going to continue that discussion. Both sides have convincing arguments and I don’t really want to advocate for one side here.

Instead I’m going to talk about something else related to the C++ move semantics, that couldn’t fit into the original post: The relationship between a default constructor and move semantics.

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Author's profile picture Jonathan

Standardese documentation generator version 0.2: Entity linking, index generation & more

Two months ago I’ve released standardese version 0.1. I promised that the next version wouldn’t take so long as the first one - which took one month.

Well, I’m really not good as estimates.

But this release brings the last missing features to make standardese an actually usable documentation generator: index generation, referring to other parts of the documentation and more output formats, as well as other amazing features like an overhauled comment system. Also a lot of internal changes and bug fixes.

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Author's profile picture Jonathan

Move safety - know what can be done in the moved-from state

C++ programmers have this notion of exception safety. It is a very useful concept. With it one can easily describe the post-conditions of a function if it throws.

There is another situation where you need to easily describe some post-conditions: when talking about the state of an object after a move operation, i.e. after a move constructor or move assignment operator. I thus want to introduce vocabulary for those post-conditions of the right-hand argument similar to the exception safety of a function: The move safety, if you will.

The exception safety describes the post-conditions of a function if the function throws an exception. Similarly, the move safety describes the post-conditions of the object after a move operation. It thus gives information about what can be done safely with a moved-from object.

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Author's profile picture Jonathan

Tutorial: Easy dependency management for C++ with CMake and Git

C++ dependency management is a more controversial topic with many alternatives and lots of third-party tools. The following reddit comment describes it well:

This tutorial explains a relatively simple solution using CMake - the de-facto standard build tool - and git - the de-facto source code version control system. It doesn’t require any external tools, works on all platforms and is relatively easy to setup and flexible for the user. This is the same system I’m currently using for standardese, my C++ documentation generator.

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Author's profile picture Jonathan

Flexible error handling techniques in C++

Sometimes things aren’t working. The user enters stuff in the wrong format, a file isn’t found, a network connection fails and the system runs out of memory. Those are errors and they need to be handling.

In a high-level function this is relatively easy. You know exactly why something was wrong and can handle it in the right way. But for low-level functions this isn’t quite as easy. They don’t know what was wrong, they only know that something was wrong and need to report it to their caller.

In C++ there are two main strategies: error return codes and exceptions. The “modern”, mainstream C++ way of handling errors are exceptions. But some people cannot use/think they cannot use/don’t want exceptions - for whatever reason.

This blog post isn’t going to pick a side on the fight. Instead I am describing techniques that make both sides - relatively - happy. Those techniques are especially useful if you are developing libraries.

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Author's profile picture Jonathan

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