cpp

CLI11, a powerful library for writing beautiful command line interfaces in C++11, has been updated to 1.3, the largest update ever. CLI11 is more powerful than ever, and has simpler and more consistent parsing under the hood.

This version focused on refactoring several key systems to ensure correct behavior in the interaction of different settings. Most caveats about features only working on the main App have been addressed, and extra arguments have been reworked. Inheritance of defaults makes configuring CLI11 much easier without having to subclass. Policies add new ways to handle multiple arguments to match your favorite CLI programs. Error messages and help messages are better and more flexible. Several bugs and odd behaviors in the parser have been fixed.

CLI11, a powerful library for writing command line interfaces in C++11, has just been released. There are no requirements beyond C++11 support (and even <regex> support not required). It works on Mac, Linux, and Windows, and has 100% test coverage on all three systems. You can simply drop in a single header file (CLI11.hpp available in releases) to use CLI11 in your own application. Other ways to integrate it into a build system are listed in the README.

The library was inspired the Python libraries Plumbum and Click, and incorporates many of their user friendly features. The library is extensively documented, with a friendly introduction, a tutorial filled (in progress) GitBook, and more technical API docs.

I often see perfect forwarding listed for constructor arguments, but not usually for functions with a return or methods. Here is my solution for an method method of class Cls:

template<typename ...Args>
static auto method(Cls* cls, Args &&  ...args)
  -> typename std::result_of<decltype(&Cls::method)(Cls, Args...)>::type {
    return cls->method(std::forward<Args>(args)...);
}

This is useful if you want to call protected classes from a “helper” friend class, for example, to expose them to tests without having to require GoogleTest/GoogleMock to be available for regular users.

The every-three-year cycle has changed the development of C++; we are now getting consistent releases somewhere in-between the major and minor releases of old. The 2017 release may be called minor by some, with a huge portion of the planned improvements being pushed back another 3-6 years, but there were several substantial changes in useful areas; it is much more impactful than C++14, for example. This almost feels like a lead-in release to C++20.

The std::variant, std::optional, and std::any additions to the standard library are huge, and can restructure the way you program (and are available for older C++ releases through Boost and other libraries).

Unlike C++11, this is a minor release, focused mostly on improvements on top of C++11 changes, with very little that one could call “new”. C++14 feels a little more natural than C++11 by expanding the usage of features and implementing common sense additions that were missed in the original C++11 release. There were also quite a few bug fixes; several of these were backported into C++11 mode in compilers.

Also, while C++11 is always available in ROOT 6, C++14 requires a flag and compatible compiler, so C++14 features are often unavailable. The Conda-Forge ROOT package has C++17 enabled.

C++11 was the largest change ever made to C++; and due to the changed release schedule, probably will remain the largest single change. It is a well thought out, mostly backward-compatible change that can cause you to completely rethink the way you write code in C++. It is best thought of as almost a new language, a sort of (C++)++ language. There are too many changes to list here, and there are excellent resources available, so this is meant to just give you a taste of some of the most useful changes.

Many of the features work best together, or are related. There already are great resources for learning about C++11 (listed at the bottom of this lesson), and C++11 is already in use in most software. Therefore, the remainder of this lesson will cover a few of the common idioms in C++11 that a programmer experienced with the older C++ might not immediately think of.