Hi, I'm Tomasz

Recently, I’ve learned about constexpr virtual functions. The support for which was added along with C++20. C++23 additionally allows for constexpr new (with some restrictions). There’s a great article about constexpr virtual on C++ stories blog, followed by another great post about constexpr new. I highly recommend reading Bartek’s posts.

Wanting to add this new feature to my tool belt I was wondering what would be the best application for constexpr virtual and how would I use them in my code.

Introduction of concepts in c++20 brought along a new set of problems requiring solving related to wrapper types (like e.g. std::optional, std::variant).

Specifically, special functions (like constructors, copy constructors, destructors etc) need to have the same type of traits as the type they are wrapping i.e. these have to be copyable if the underlying type is copyable, trivially copyable if the underlying types are trivially copyable, and trivially destructible if the underlying types are trivially destructible.

Sure, = default is great and convenient especially for destructors and other special member functions but when declaring a class that’s meant to be a part of a shared library’s interface I try to avoid using it and here’s my reasons why.

TLDR

Problem definition

Let’s start with a simple abstract class declared in a header file (calc.hpp):

Welcome to the second part of the series about dependency and package management in C++ projects. This time I’m gonna focus on somewhat less popular solutions than the main three.

Overview

Let’s evaluate if any of these are worth the hassle.

Hunter

Hunter caters towards CMake. The way it works is really similar to meson’s wraps (with the only difference that it’s not built into CMake). Usage is fairly simple. You have to export HUNTER_ROOT to a location of choice. Hunter will use it to store its build directories and obtained source code. There’s nothing that has to be installed. It’s kind of “self bootstrapping”. You have to download HunterGate within your CMake project:

This post is a quick reminder to self regarding specifics of RPATH, RUNPATH, LD_LIBRARY_PATH, LD_RUN_PATH and the lookup order.

Refresher (a very short one)

RPATH, RUNPATH - are entries in the ELF header, baked into the binary allowing the dynamic loader to lookup its shared dependencies.

RPATH/RUNPATH can be specified directly, using a linker option (-rpath):

g++ -Wl,-rpath=path/for/rpath

If missing in the command line, RPATH can be set using LD_RUN_PATH variable.

In this post I’m gonna do a short overview of package management and vendoring solutions for C++. This is a controversial topic. Still, there’s no official standardised package manager however, there’s a plethora of solutions (some more mature than others) which I think solve the problem well (at least as far as I’m concerned). I planned to publish the entire overview in a single post however, there’s a lot of material to cover and eventually I had to split it up into multiple parts.

Let’s suppose that you’re working with a virtual interface defined as follows:

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struct I {
    virtual ~I() = default;

    virtual void process(int) = 0;
};

Now, let’s have a class A that implements this interface:

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struct A : I {
    void process(int) override {}
};

So far so good. Now, let’s say you want to add an overloaded version of process in class B. This would look like so:

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struct B : A {
    void process(std::string) {}
};

An attempt to use this class’s original interface like so: