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The Move Constructor That You Have to Declare, Even Though You Don’t ... -- Raymond Chen

By Blog Staff | Jul 4, 2023 05:07 PM | Tags: None

You may have a class that you want to participate in RVO or NRVO, but you also don’t want it to be moved. For example, it may contain a std::mutex, which is not movable. But you nevertheless have to declare a move constructor. What can you do?

The Move Constructor That You Have to Declare, Even Though You Don’t Want Anyone to Actually Call It

by Raymond Chen

From the article:

Blah blah blah C++ return value optimization (RVO), named return value optimization (NRVO), and copy elision.

RVO support was optional in C++11 but became mandatory in C++17. NRVO support remains optional (but recommended).

To allow NRVO in C++17 (or RVO and NRVO in C++11), a move constructor must be available, even though the compiler will not call it if the optimization is employed.

You may have a class that you want to participate in RVO or NRVO, but you also don’t want it to be moved. For example, it may contain a std::mutex, which is not movable. But you nevertheless have to declare a move constructor. What can you do?

Declare the move constructor, but...

Need Something Sorted? Sleep On It! -- Kevlin Henney

By Blog Staff | Jul 3, 2023 10:49 AM | Tags: None

Sorting algorithms have been thoroughly studied. Kevlin Henney takes an unexpected paradigm journey into sleep sort.

Need Something Sorted? Sleep On It!

by Kevlin Henney

From the article:

A decade ago, I first presented a lightning talk entitled ‘Cool Code’. This short talk evolved into a full talk whose iterations I presented over the next half decade. The focus? Code that, for some reason or other, can be considered cool. For example, code that has played a significant role in historical events, such as the source for the Apollo Guidance Computer [Apollo]. Or code that is audacious – if not seemingly impossible – given its constraints, such as David Horne’s 1K chess [Frogley01]. There is code that is both simple and profound, such as Peter Norvig’s fits-on-a-slide spelling corrector [Norvig16]. And code that demonstrates ingenuity and humour, such as Yusuke Endoh’s Qlobe [Endoh10].

Leaving aside its content for a moment, one of the most interesting things about the talk was its...

Modern C++ In-Depth — Transparent Comparisons

By Jens Maurer | Jul 3, 2023 02:20 AM | Tags: intermediate c++14

Less overhead for associative container lookup

Modern C++ In-Depth — Transparent Comparisons

by Michael Kristofik

From the article:

Searching for an element in a container normally requires constructing an object of the container’s key_type. If the key is small, such as one you’d normally pass by value, it isn’t a performance concern. But what if the key is large?

CppCon 2022 Using Modern C++ to Eliminate Virtual Functions -- Jonathan Gopel

By Blog Staff | Jun 30, 2023 04:56 PM | Tags: None

Registration is now open for CppCon 2023! The conference starts on October 1 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2023!

Using Modern C++ to Eliminate Virtual Functions

by Jonathan Gopel

Summary of the talk:

As of C++20, there are no cases in which statically linked programs require virtual functions. This talk will explore techniques for replacing runtime polymorphism with compile-time polymorphism such that virtual functions are never necessary. This talk will also address the higher-order concern of when it might make sense to avoid virtual functions or remove them from a codebase, as that decision ultimately is a design decision that only the author of the code can make. Attendees can expect to come away with a stronger understanding of the purposes of virtual functions and the mechanisms in modern C++ that can now be used to achieve those same purposes.

Why You Should Only Rarely Use std::move -- Andreas Fertig

By Blog Staff | Jun 30, 2023 10:40 AM | Tags: None

std::move can allow the efficient transfer of resources from object to to object. Andreas Fertig reminds us that using std::move inappropriately can make code less efficient.

Why You Should Only Rarely Use std::move

by Andreas Fertig

From the article:

The example in Listing 1 is the code I used to make my point: don’t use std::move on temporaries! Plus, in general, trust the compiler and only use std::move rarely. For this article, let’s focus on the example code.
class S {
public:
  S() { printf("default constructor\n"); }
  ~S() { printf("deconstructor\n"); }
  // Copy constructor ①
  S(const S&) { printf("copy constructor\n"); }
  // Move constructor ②
  S(S&&) { printf("move constructor\n"); }
};
void Use()
{
  S obj{
    S{} // Creating obj with a temporary of S ③
  };
}
Listing 1
Here we see a, well, perfectly movable class. I left the assignment operations out. They are not relevant. Aside from the constructor and destructor, we see in ① the copy constructor and in ② the move constructor. All special members print a message to identify them when they are called.
Further down in Use, we see ③, a temporary object of S used to initialize obj, also of type S. This is the typical situation where move semantics excels over a copy (assuming the class in question has movable members). The output I expect, and I wanted to show my participants, is:

Type Safe C++ enum Extensions -- Alf Steinbach

By Blog Staff | Jun 28, 2023 07:36 AM | Tags: None

Is it possible to extend a value type in C++? Alf Steinbach describes how to extend enum values.

Type Safe C++ enum Extensions

by Alf Steinbach

From the article:

Consider if an enum like the following,
  enum class Suit{
  spades, hearts, diamonds, clubs };
could be extended like
  enum class Suit_with_joker extends Suit {
    joker };
where

Suit_with_joker has all the enumerators of Suit plus the joker enumerator; and

enumerators introduced in Suit_with_joker get integer values following those of Suit; and

any Suit value is also a Suit_with_joker value.

This would be an example of what I’ll call a value type extension.

The apparently backwards is-a relationship in the last point, where any value of the original type is-a value of the derived type, is characteristic of value type extensions.

C++20 totally lacks support for value type extensions, of enum types or other types.

CppCon 2022 Finding Whether a Number is a Power of 2 -- Ankur Satle

By Blog Staff | Jun 27, 2023 04:50 PM | Tags: None

Lightning Talk: Finding Whether a Number is a Power of 2

by Ankur Satle

Summary of the talk:

I asked this question on social media and got many diverse responses. I will present the various approaches and compare them. I will finish with the options C++20 provides with the bit header. https://en.cppreference.com/w/cpp/numeric/has_single_bit

CppCon 2022 Who is Looking for a C++ Job? -- Jens Weller

By Blog Staff | Jun 26, 2023 04:48 PM | Tags: None

Lightning Talk: Who is Looking for a C++ Job?

by Jens Weller

Summary of the talk:

A few insights on who has been applying for C++ jobs and visited the Meeting C++ online job fairs.

It’s Great That You Provide Operator Overloads, But It’s Also Nice to Have Names -- Raymond Chen

By Blog Staff | Jun 25, 2023 05:08 PM | Tags: None

Operator overloading. Looks great. Reduces verbosity. Until it doesn’t.

It’s Great That You Provide Operator Overloads, But It’s Also Nice to Have Names

by Raymond Chen

From the article:

Consider this overloaded function call operator:
struct StorageLoader
{
    template<DataType>
    DataType operator()(StorageOptions<DataType> const* options);
};
The idea is that you can use the function call operator on a StorageLoader object to load data from storage, using a StorageOptions to describe how you want it to be loaded.

CppCon 2022 Template Meta-Programming in C++ -- Kris Jusiak

By Blog Staff | Jun 23, 2023 04:42 PM | Tags: None

Lightning Talk: MP: Template Meta-Programming in C++

by Kris Jusiak

Summary of the talk:

In this lightning talk, Kris attempts to teach template meta-programming in 5 minutes with the use of C++20 and ranges.