Articles & Books

Visiting variants using lambdas (2: recursive variants)—Vittorio Romeo

The article addresses the problem of lambda-based `std::variant` and `boost::variant` recursive visitation. Starting from the definition of a "recursive variant", it shows the concept and implementation behind a `make_recursive_visitor` variadic function that can be used to create "local" visitors by using lambdas.

visiting variants using lambdas - part 2

By Vittorio Romeo

From the article:

A "recursive" variant is a variant which can contain itself, and can be used to represent recursive structures. [...] Bringing algebraic data types from the functional programming world into C++ isn't enough - we're also going to adopt another powerful construct: the Y Combinator. [...] Now we can put everything together to finally visit a recursive variant using lambdas!

Tutorial: Emulating strong/opaque typedefs in C++—Jonathan Müller

Who would like this feature?

Tutorial: Emulating strong/opaque typedefs in C++

by Jonathan Müller

From the article:

Last week, I’ve released my type_safe library. I described it’s features in the corresponding blog post but because the blog post got rather long, I couldn’t cover one feature: strong typedefs.

Strong or opaque typedefs are a very powerful feature if you want to prevent errors with the type system - and as I’ve been advocating for, you want that. Unlike “normal” typedefs, they are a true type definition: they create a new type and allow stuff like overloading on them and/or prevent implicit conversions.

Visiting variants using lambdas (1) - - Vittorio Romeo

The article covers a technique that allows variant types (both `std::variant` and `boost::variant`) to be visited using lambdas, without having to explicitly create a functor.

visiting variants using lambdas - part 1

By Vittorio Romeo

From the article:

Visiting a variant is usually done by writing a visitor struct/class outside of the scope where the variant is actually being visited. [...] It is possible to build such an object locally in the call site [...] by implementing something similar to `std::overload`.

The “unsigned” Conundrum—Tony “Bulldozer00” DaSilva

Are you clear with unsigned?

The “unsigned” Conundrum

by Tony “Bulldozer00” DaSilva

From the article:

A few weeks ago, CppCon16 conference organizer Jon Kalb gave a great little lightning talk titled “unsigned: A Guideline For Better Code“. Right up front, he asked the audience what they thought this code would print out to the standard console:

Even though -1 is obviously less 1, the program prints out “a is not less than b“. WTF?

Overload 135 is now available

ACCU’s Overload journal of October 2016 is out. It contains the following C++ related articles.

Overload 135 is now available

From the journal:

Determinism: Requirements vs Features
A program can easily be non-deterministic. Sergey Ignatchenko considers how to define determinism. by Sergey Ignatchenko

Eight Rooty Pieces
Finding a square root is a common interview question. Patrick Martin demonstrates eight different ways to find a root. by Patrick Martin

Polymorphic Comparisons
Polymorphic comparisons require much boilerplate. Robert Mill and Jonathan Coe introduce a template utility for such comparisons. by Robert Mill and Jonathan Coe

C++ Synchronous Continuation Passing Style
Direct and continuation passing styles differ. Nick Weatherhead explains a continuation passing style for synchronous data flow. by Nick Weatherhead

Attacking Licensing Problems with C++
Software licenses are often crackable. Deák Ferenc presents a technique for tackling this problem. by Deák Ferenc

camomilla: C++ error simplification script - - Vittorio Romeo

Article covering "camomilla", a Python script designed to post-process heavily-template-based C++ errors in order to make them easier to read.

camomilla: C++ error simplification script

by Vittorio Romeo

From the article:

camomilla uses simple text transformations to make gcc and clang errors smaller and easier to read. [...] The main text transformation used by camomilla to prevent full expansion of templates is "template typename collapsing", which hides nested typenames up to a user-specified depth. [...] The two other current transformations offered by camomilla are simple regex replacements that can act on namespaces or generic symbols. They can be defined in .json configuration files (which can recursively include each other!) [...] camomilla helps with [continuously transforming the same error] by automatically caching the last processed original error, so that the user can play around with different transformations and options.

DLib 19.2 released

Today a new version of DLib is available:

DLib 19.2 released

Release notes

by Davis King

From the article:

... So the obvious thing to do was to add an implementation of MMOD with the HOG feature extraction replaced with a convolutional neural network.  The new version of dlib, v19.2, contains just such a thing.  On this page you can see a short tutorial showing how to train a convolutional neural network using the MMOD loss function.  It uses dlib's new deep learning API to train the detector end-to-end on the very same 4 image dataset used in the HOG version of the example program.  Happily, and very much to the surprise of myself and my colleagues, it learns a working face detector from this tiny dataset.

Optimizing return values—Marco Foco

Marco Foco shows different solutions and tradeoffs to a dangling reference problem:

Optimizing return values

    by Marco Foco

From the article:

As you can see, class C contains a function get() which returns a reference to its internal state. In normal code, we must take care not to use this reference after our class has been destroyed...

Quick Q: Is the ‘override’ keyword just a check for a overriden virtual method?

Quick A: Yes.

Recently on SO:

Is the 'override' keyword just a check for a overriden virtual method?

That's indeed the idea. The point is that you are explicit about what you mean, so that an otherwise silent error can be diagnosed:

struct Base
    virtual int foo() const;

struct Derived : Base
    virtual int foo()   // whoops!
       // ...

The above code compiles, but is not what you may have meant (note the missing const). If you said instead, virtual int foo() override, then you would get a compiler error that your function is not in fact overriding anything.