Keynotes at Meeting C++ 2017

With the conference just a few weeks away, an update on the 3 awesome keynotes of this years Meeting C++:

Keynotes at Meeting C++ 2017

by Jens Weller

From the article:

Are you excited for Meeting C++ 2017?!? I quickly wanted to give an update on the 3 keynotes at the conference this year! Each day will feature one keynote, where the first two are in the morning, while the Closing Keynote is kind of the last thing to happen before the closing message. Also, all 3 keynote speakers have now (finally) their speaker profile.

CppCon 2017: What Has My Compiler Done for Me Lately? Unbolting the Compiler’s Lid—Matt Godbolt

The CppCon 2017 endnote is now available! What an excellent talk by Matt, of Godbolt fame.

What Has My Compiler Done for Me Lately? Unbolting the Compiler's Lid

by Matt Godbolt

From the article:

In 2012, Matt and a colleague were arguing whether it was efficient to use the then-new-fangled range for. During the discussion a bash script was written to quickly compile C++ source and dump the assembly. Five years later and that script has grown into a website relied on by many to quickly see the code their compiler emits, to compare different compilers' code generation and behaviour, to quickly prototype and share code, and investigate the effect of optimization flags.

In this talk Matt will not only show you how easy (and fun!) it is to understand the assembly code generated by your compiler, but also how important it can be. He'll explain how he uses Compiler Explorer in his day job programming low-latency trading systems, and show some real-world examples. He'll demystify assembly code and give you the tools to understand and appreciate how hard your compiler works for you.

He'll also talk a little about how Compiler Explorer works behind the scenes, how it is maintained and deployed, and  share some stories about how it has changed over the years. By the end of this session you'll be itching to take your favourite code snippets and start exploring what your compiler does with them.

Detection Idiom - A Stopgap for Concepts—Simon Brand

Concepts are not yet here, but there are solutions.

Detection Idiom - A Stopgap for Concepts

by Simon Brand

From the article:

Concepts is a proposed C++ feature which allows succinct, expressive, and powerful constraining of templates. They have been threatening to get in to C++ for a long time now, with the first proposal being rejected for C++11. They were finally merged in to C++20 a few months ago, which means we need to hold on for another few years before they’re in the official standard rather than a Technical Specification. In the mean time, there have been various attempts to implement parts of concepts as a library so that we can have access to some of the power of Concepts without waiting for the new standard. The detection idiom – designed by Walter Brown and part of the Library Fundamentals 2 Technical Specification – is one such solution. This post will outline the utility of it, and show the techniques which underlie its implementation.

Automatic two-phase init—Krzysztof Ostrowski

Deferred initialisation for classes that inherit constructors, or Automatic two-phase init.

Deferred initialisation for classes that inherit constructors

by Krzysztof Ostrowski

From the article:

Constructor inheritance through using-declaration is a powerful technique that can be easily used to introduce pre-defined behaviour to custom types. As an example, consider a generic visitor design pattern implementation that is parametrised by the names of visitable types, and an unique tag that identifies given visitor template instance. Such an instance can be "mixed-in" into a custom type D by simply deriving from it... and inheriting its constructors to make it behave as it would be a Visitor template instance itself:

struct D
  : Visitor<
        A         // the tag
      , X, Y, Z   // "list" of visitable types
    using Visitor::Visitor;
What if there is a need to run an "additional" initialisation code as it would be run in the D constructor if one were there? Bjarne Stroustrup suggests member-initializers that do half of a work we would like to do here. While direct member initialisation sets required initial values for all the members (except bit field members), it does not offer a direct way to execute custom code that makes use of those members, the custom code that typically resides in the constructor's body.
This article presents a solution that enables injection of a custom code to be executed once all the non-static members are initialised.

CppCon 2016: Regular Expressions in C++, Present and Future—Tim Shen

Have you registered for CppCon 2017 in September? Don’t delay – Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2016 for you to enjoy. Here is today’s feature:

Regular Expressions in C++, Present and Future

by Tim Shen

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Regular expressions are widely used in application development and data processing, yet it is challenging to design and implement a regular expression library that is expressive, efficient and safe.

In this talk, Tim Shen, the current maintainer of libstdc++'s <regex>, will introduce the basics of implementing regular expressions in C++, the status of existing implementations, and what is expected from the standardization process.

For the implementation, several data structures and algorithms will be introduced, with pros and cons listed; we will show how several popular implementations (Boost.Regex, Boost.Xpressive, <regex> from standard library implementations, RE2, etc) pick their algorithms. Several popular features/patterns that hurt performance will be explained, with a "safe" regex usage suggested. Finally a wishlist of features will be presented, in order to deliver a more efficient and usable regex library.

Quick Q: How to require an exact function signature in the detection idiom?

Quick A: Use is_detected

Recently on SO:

How to require an exact function signature in the detection idiom?

With C++17 is_detected, you may do

template <typename T, typename Ret, typename Index>
using subscript_t = std::integral_constant<Ret (T::*) (Index), & T::operator[]>;

template <typename T, typename Ret, typename Index>
using has_subscript = is_detected<subscript_t, T, Ret, Index>;

static_assert(has_subscript<std::vector<int>, int&, std::size_t>::value, "!");
static_assert(!has_subscript<std::vector<int>, int&, int>::value, "!");

Zero-allocation continuations in C++17 — Vittorio Romeo

This series of articles show the design and implementation of future-like asynchronous computation chains that do not require any dynamic memory allocation or type erasure. 

by Vittorio Romero

From the article:

I'd like to show an alternative design [for futures] that doesn't require any allocation whatsoever and still enables users to build up asynchronous computation chains using facilities such as `when_all` and `.then`. [...] The idea behind it is to encode the entire computation chain into a single object with a huge type.