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Trip report: February 2019 ISO C++ committee meeting, Kona, Hawai’i--Timur Doumler

By Adrien Hamelin | Mar 5, 2019 01:21 PM | Tags: community

Another report.

Trip report: February 2019 ISO C++ committee meeting, Kona, Hawai’i

by Timur Doumler

From the article:

What better way to start my new blog than to publish a trip report from the most recent C++ committee meeting on the wonderful Big Island of Hawai’i?

If you are looking for an incredibly detailed report of everything that happened, please instead head to this report by Bryce and others, and also see Herb Sutter’s and cor3ntin’s reports. I won’t try to provide this breadth of coverage, and instead focus on a few areas that are particularly relevant for me and the community that I am proxying here:

  • Making C++ simpler, more uniform, and easier to teach;
  • Providing developers with better tools;
  • Improving support for low-latency and real-time(-ish) programming,
  • 2D Graphics, Audio, and other forms of I/O and human-machine interaction.

That being said, let’s start with the big news: we voted both Coroutines and Modules into C++20!

Quick Q: Implicit conversion and operator overload

By Adrien Hamelin | Mar 4, 2019 01:08 PM | Tags: intermediate

Quick A: it tries to convert to int.

Recently on SO:

Implicit conversion and operator overload

In comparing the conversions needed by different overloaded functions, a "promotion" is considered a better conversion sequence than a standard "conversion". Every arithmetic type can promote to at most one other type. (Promotions are also used when passing an argument to a C-style variadic function like printf. The unary + operator can be used to force a promotion of an arithmetic expression, like +n.)

For integer types which are not character types or bool, the promoted type is:

  • If int can represent all the values of the original type, then int;
  • Otherwise, if unsigned int can represent all the values of the original type, then unsigned int;
  • Otherwise, the original type itself (promotion does nothing)

In your example, when comparing the overloaded functions, an "exact match" would be best, but there is no function taking exactly int8_t (or int8_t& or const int8_t&). The promoted type of uint8_t is int, since it's required to support a range much larger than 0-255. And apparently on your system, int32_t is an alias for int, so the function void f(int32_t); requires only a promotion on the argument. The other functions are all viable, but require an integer conversion on the argument. So void f(int32_t); is considered the best overload.

So the technical answer to the question is that it is implementation specific, but only because of the relationship between int and the <cstdint> types, not because of the overload resolution rules.

C++ User Group Meetings in March

By Meeting C++ | Mar 1, 2019 06:16 AM | Tags: user groups meetingcpp community

The monthly overview on upcoming C++ User Group meetings by Meeting C++

C++ USer Group Meetings in March 2019

by Jens Weller

From the article

The monthly overview of upcoming C++ User Group meetings! Lots of groups already announced their meetings, if your group is not in the list, they might announce later.

Want to speak at a User Group? Use the contact form to reach out to several User Groups that you'd be able to visit for a talk!

There are 4 new C++ User Groups...

Overload 149 is now available

By Adrien Hamelin | Feb 25, 2019 12:35 PM | Tags: community

ACCU’s Overload journal of February 2019 is out. It contains the following C++ related articles.

Overload 149 is now available

From the journal:

Rip It Up and Start Again.
Some things can be resurrected, others cannot. Frances Buontempo wonders when we need to repent and start over.

5 Big Fat Reasons Why Mutexes Suck Big Time.
Mutable shared state in multithreaded code is often protected by mutexes. Sergey Ignatchenko reminds us that Re-Actors can avoid many of the problems.

A Small Universe.
Writing a programming language is a hot topic. Deák Ferenc shows us how he wrote a compiler for bytecode callable from C++.

QM Bites: Understand Windows Operating-System Identification Preprocessor Macros.
Quality matters and bite sized articles help. Matthew Wilson returns with a QM Bites.

A Thorough Introduction to Distributed Systems.
What is a distributed system, and why is it so complicated? Stanislav Kozlovski explains.

Don’t Use std::endl.
How do you add a new line in C++? Chris Sharpe suggests std::endl is a tiny utility that’s more trouble than it’s worth.

Cpp On Sea 2019 Trip Report--Arne Mertz

By Adrien Hamelin | Feb 20, 2019 01:12 PM | Tags: community

Were you there?

Cpp On Sea 2019 Trip Report

by Arne Mertz

From the article:

From February 3rd through February 6th I have been in Folkestone, UK, to visit the first C++ On Sea conference.

There must be something in the water on that island that enables them to organize fantastic conferences like ACCUConf and, since this year, C++ On Sea.
C++ On Sea is definitely the best conference I have ever been to, and here’s a little glimpse why I think so...

2 Lines Of Code and 3 C++17 Features - The overload Pattern--Bartlomiej Filipek

By Adrien Hamelin | Feb 18, 2019 11:26 AM | Tags: c++17 advanced

Proof that you can do more!

2 Lines Of Code and 3 C++17 Features - The overload Pattern

by Bartlomiej Filipek

From the article:

While I was doing research for my book and blog posts about C++17 several times I stumbled upon this pattern for visitation of std::variant:

template<class... Ts> struct overload : Ts... { using Ts::operator()...; };
template<class... Ts> overload(Ts...) -> overload<Ts...>;

std::variant<int, float> intFloat { 0.0f };
std::visit(overload(
    [](const int& i) { ... },
    [](const float& f) { ... },
  ),
  intFloat;
);

With the above pattern, you can provide separate lambdas “in-place” for visitation.

It’s just two lines of compact C++ code, but it packs a few interesting concepts.

Let’s see how this thing works and go through the three new C++17 features that enable this one by one.