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Quick Q: Is std::unique_ptr required to know the full definition of T?

By Adrien Hamelin | Sep 21, 2020 11:53 AM | Tags: intermediate

Quick A: For certain members only.

Recently on SO:

Is std::unique_ptr<T> required to know the full definition of T?

Most templates in the C++ standard library require that they be instantiated with complete types. However shared_ptr and unique_ptr are partial exceptions. Some, but not all of their members can be instantiated with incomplete types. The motivation for this is to support idioms such as pimpl using smart pointers, and without risking undefined behavior...

What std::exchange does, and how to remember it--Jonathan Boccara

By Adrien Hamelin | Sep 18, 2020 10:49 AM | Tags: stl

If you had troubles.

What std::exchange does, and how to remember it

by Jonathan Boccara

From the article:

std::exchange was introduced in the C++ standard library in C++14 under the header <utility>.

Its name suggests that it’s a general-purpose and useful function, and its template prototype working with any type confirms this impression.

I don’t know about you, but I always had a problem with std::exchange: I couldn’t remember what it was doing. I learnt several times the operations that std::exchange performs, but each time I forgot them soon after.

Then at some point it clicked: std::exchange is a setter returning the old value. Ignoring the name “exchange” but thinking of it as a “setter” helped me make it stick to my mind.

It might just be me having a hard time with std::exchange for some reason. But just in case you also have issues remembering the operations of std::exchange, let’s see why std::exchange has this meaning, and why this meaning is not obvious from its name.

This should help you remember it once and for all...

Concept archetypes — update--Andrzej Krzemieński

By Adrien Hamelin | Sep 17, 2020 10:57 AM | Tags: c++20

Not so easy, but still useful.

Concept archetypes — update

by Andrzej Krzemieński

From the article:

An observant reader indicated that in the previous post where I was trying to implement a concept archetype — a type with minimal interface that models a given concept — I actually failed. This deserves a closer examination...

Refactoring from single to multi purpose

By Meeting C++ | Sep 16, 2020 05:50 AM | Tags: meetingcpp intermediate experimental community c++14 basics

Working on an old project, it came to my mind that I do this refactoring from one static path to multiple options for the 2nd time this year...

Refactoring from single to multi purpose

by Jens Weller

From the article:

For the second time this year I'm refactoring a program from a single purpose to have two or more modes of operation. Both times the start and end result is similar, just the processing is different. A classic case of using polymorphism.

The first program was a tool to process videos from speakers, find a face and export the subframe around it into a new video. The first mode was a good approach to test it, and gave results for some speakers. The second mode did a complete scan first, and then gave a smoother video for some videos. Still, both modes had to be retained...

Replacing unique_ptr with C++17's std::variant a Practical Experiment--Bartlomiej Filipek

By Adrien Hamelin | Sep 15, 2020 11:16 AM | Tags: c++17

variant shows his capabilities.

Replacing unique_ptr with C++17's std::variant a Practical Experiment

by Bartlomiej Filipek

From the article:

Some time ago I wrote about a new way to implement runtime polymorphism which is based not on virtual functions but on std::visit and std::variant. Please have a look at this new blog post where I experiment with this approach on my home project. The experiment is more practical than artificial examples.

See advantages, disadvantages and practical code issues.

Concept archetypes--Andrzej Krzemieński

By Adrien Hamelin | Sep 3, 2020 12:00 PM | Tags: c++20

Testing custom concepts.

Concept archetypes

by Andrzej Krzemieński

From the article:

Concepts in the form added in C++20 used to be called lite. This is because they do not provide one quite important functionality: having the compiler check if the author of a constrained template is only using operations and types allowed by the constraining concept. In other words, we can say that our template only requires operations A and B to be valid, but we can still use some other operations inside and this is fine with the compiler. In this post we will show how this is problematic, even for programmers aware of the issue, and how to address it with concept archetypes...