Meeting 17 August 2017

VS2017.3 (15.3) released

Accessibility improvements
C++17 Features And STL Fixes In VS 2017 15.3 by STL
- The STL now uses C++14 constexpr unconditionally, instead of conditionally-defined macros.
- The STL now uses alias templates internally.
- The STL now uses std::move() internally, instead of stylistically misusing std::forward().
- The STL no longer marks functions as __declspec(dllimport). Modern linker technology no longer requires this (???)

Passing parameters to constructors

1class Foo {
2public:
3    Foo(Bar bar, Baz baz)
4    : bar_(std::move(bar))
5    , baz_(std::move(baz))
6    {}
7};

Is this better than using const references?

C++ Core Guidelines: passing consume parameters

p0052r5 - Generic Scope Guard and RAII Wrapper for the Standard Library

PDF

1auto scope_exit = make_scope_exit([&]{ /* always */ });
2auto scope_success = make_scope_success([&]{ /* successful scope exit */ });
3auto scope_fail = make_scope_fail([&]{ /* exception */ });

Compare with GSL’s finally Link

p0053r6 - C++ Synchronized Buffered Ostream

PDF

We propose a basic_osyncstream, that buffers output operations for a wrapped stream. The basic_osyncstream will atomically transfer the contents of an internal stream buffer to a basic_ostream’s stream buffer on destruction of the basic_osyncstream.

Example:

1osyncstream{cout} << "The answer is " << 6*7 << endl;

Familiar template syntax for generic lambdas

PDF

C++14:

1[](auto x) { /* ... */ }

Proposed:

1[]<typename T>(T x) { /* ... */ }
2[]<typename T>(T* p) { /* ... */ }
3[]<typename T, int N>(T (&a)[N]) { /* ... */ }

C++ Coroutine TS Issues

Link

Feedback, edits/diffs, discussions.

Your own error code

Post

System error support in C++0x by Chris Kohlhoff: Part 1, Part 2, Part 3, Part 4, Part 5
std::error_code

DIMWITS: DIMensional analysis With unITS

 1/* quantities play nicely with auto */
 2auto myVelocity = 1.0 * meter / second;
 3std::cout << "The speed is: " << myVelocity << std::endl;
 4
 5/* quantities of the same dimensionality can be implicitly converted */
 6Quantity<Foot> myLength = 1.0 * meter;
 7std::cout << "1 meter in feet is: " << myLength << std::endl;
 8
 9/* si-prefixes can be specified on either side of the assignment */
10Quantity<Kilo<Gram>> myMass = 1.0 * mega(tonne);
11std::cout << "1 megatonne in kilograms is: " << myMass << std::endl;
12
13/* NIST values for common physical constants are provided */
14std::cout << "The speed of light is: " << constant::lightSpeed << std::endl;

sltbench: a C++ micro-benchmarking tool

GitHub – Apache 2.0 licence

4.7x times faster than googlebench

1void my_function()
2{
3    std::vector<size_t> v(100000, 0);
4    std::sort(v.begin(), v.end());
5}
6
7SLTBENCH_FUNCTION(my_function);
8
9SLTBENCH_MAIN();

spdlog: an ultra-fast C++ logging library

GitHub – C++11, MIT licence

header-only
Linux, FreeBSD, Solaris, Mac OS, Windows, Android
Uses {fmt} library for formatting
Async mode using lock-free queues
Custom formatting
Conditional logging
Targets: rotating/daily log files, console (w/colour), syslog, Windows debugger
Severity-based filtering

MPark.Variant: C++17 std::variant for C++11/14/17

GitHub – C++11, Boost Licence

Based on libc++ implementation of std::variant (same author)
Continuously tested against libc++’s std::variant test suite
Single-header
Documentation

Sweden CPP conference

Wt: a C++ web toolkit

Home page
Licence: GPL + commercial
GitHub

Beast is now a part of Boost

Boost.ASIO-based HTTP and WebSockets library
Header-only
Version 100!
Uses callbacks or coroutines
C++11
Dependencies: Boost.System, Boost.Coroutine (optional)
GitHub
Reddit thread

Italian C++ conference videos

YouTube Playlist

Towards a Good Future

P0676R0, GitHub

Based on Adobe stlab’s future and Bloomberg dplp promise
Author recommends against adoption of the proposed std::future extensions in Concurrency TS
std::future is crippled
Futures need to be copyable (currently limited to just one .then())

1future<int> a;
2a.then([](int x){ /* do something */ });
3a.then([](int x){ /* also do something else. */ }

Futures need to be cancellable

C++ Club