May 2018

Hello CMake!—Arne Mertz

Do you use it?

Hello CMake!

by Arne Mertz

From the article:

Since I have mentioned CMake in a handful of past blog posts, it is time to give a short introduction for those that don’t know it yet.

CMake is one of the most popular build systems for C++ out there. One of the main reasons probably is that it is cross-platform: It does not build the project itself but operates a platform-specific system. That means it can generate Makefiles, ninja-build files, or project files for Visual Studio or Xcode, to name just a few...

Quick Q: use of constexpr in header file

Quick A: const in a header implicitely means static.

Recently on SO:

use of constexpr in header file

constexpr implies const and const on global/namespace scope implies static (internal linkage), which means that every translation unit including this header gets its own copy of PI. The memory for that static is only going to be allocated if an address or reference to it is taken, and the address is going to be different in each translation unit.

That implied static for const variables was introduced specifically to use const instead of #define in header files in C++ to define constants. Without static there would be multiple symbol definitions linker error if that header file is included in more than one translation unit which were linked together.

In C++17 you can also make it inline, so that there is only ever a single copy of PI if an address or reference to it is taken (i.e. not static). inline variables were introduced in C++17 to allow for header-only libraries with non-const variable definitions in the header files.

In other words, you should use constexpr for your constants in header files, if possible, otherwise const. And if you require the address of that constant to be the same everywhere mark it as inline.

CppCast Episode 151: sol2 and std::embed with JeanHeyd Meneide

Episode 151 of CppCast the only podcast for C++ developers by C++ developers. In this episode Rob and Jason are joined by JeanHeyd Meneide to discuss the sol2 library and his proposal for std::embed.

CppCast Episode 151: sol2 and std::embed with JeanHeyd Meneide

by Rob Irving and Jason Turner

About the interviewee:

ThePhD -- known in meatspace as JeanHeyd -- is a Computer Science undergraduate at the Fu Foundation School of Engineering in Columbia University. They are currently working on Open Source C++ and C++ Standardization projects, as well as exploring graphics programming. They are currently dabbling with Haskell and Elm for fun, and are attempting to wrangle their biggest open source project -- sol2 -- into a newer, better version of itself. The nickname is a std::promise<> on their std::future<>.


Error Handling and std::optional—Bartlomiej Filipek

Do you have a prefered way?

Error Handling and std::optional

by Bartlomiej Filipek

From the article:

In my last two posts in the C++17 STL series, I covered how to use std::optional. This wrapper type (also called “vocabulary type”) is handy when you’d like to express that something is ‘nullable’ and might be ‘empty’. For example, you can return std::nullopt to indicate that the code generated an error… but it this the best choice?

Declarative Functional APIs – A.K.A. Abusing Lambda Parameters—Philippe Groarke

Take some time to clear your thoughts before reading!

Declarative Functional APIs – A.K.A. Abusing Lambda Parameters

by Philippe Groarke

From the article:

Functional APIs are a joy to work with. Not only do they help eliminate certain bug categories, but they tend to be very flexible and reusable. Today I present a technique that has emerged while I was simplifying some lambda based APIs. C++17 makes template meta-programming much more palatable, I dare not imagine what this would look like in C++11...

Should Span Be Regular?—Barry Revzin

Do you have an opinion?

Should Span Be Regular?

by Barry Revzin

From the article:

In my last post, I talked about the concept of Westie types (yes, I am trying to make this happen), what Regular means, and which of them are Regular. I went through an explanation for why means for span is not Regular and potentially why it should be. After lots of resulting conversations with several people (thanks Zach Laine, Nicole Mazzuca, Eric Niebler, John Shaw, Tim Song), I thought it was necessary to write a follow up with more details and more argument...

Rvalues redefined—Andrzej Krzemieński

Evolution of semantics.

Rvalues redefined

by Andrzej Krzemieński

From the article:

In this post we will explore what I consider the most significant language change in C++17. I call it the most significant because it changes the way you design your resource-managing types and how you think about initialization. It is often called “guaranteed copy elision”, but I will not use that name (except for this single time) because it does not reflect what this feature is. C++ has completely changed the meaning of rvalue (actually, prvalue)...