Implementation Challenge: Revisiting the visitor pattern

C++ as a language is moving away from the classical, “Java style”, object-oriented programming. Long gone are the days of grand, virtual hierarchies. They’ve been replaced with standalone classes, free functions and type erasure.

And the benefits are clear: Instead of reference semantics, they allow value semantics which are simpler and more natural for C++. Instead of intrusive interface inheritance, they allow external duck-typing.

So in the spirit of this movement, let’s take a look at one OOP pattern and see if we can adopt it to this style: the visitor pattern.

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Author's profile picture Jonathan

Exceptions vs expected: Let's find a compromise

This isn’t the blog post I wanted to publish today, this is the blog post I had to publish.

Simon blogged about using ADTs for error handling, leading to an interesting reddit discussion. Then Vittorio wanted to share his thoughts on the matter, leading to an even bigger reddit discussion. Now I’d like to chime in and offer a reasonable solution.

It is the age-old question: return codes vs exceptions. But this time, return codes have gotten an upgrade: std::expected and similar types.

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Author's profile picture Jonathan

What should be part of the C++ standard library?

At Meeting C++ 2017 — which was great, BTW — I attended a talk by Guy Davidson about the C++ graphics 2D proposal, wording here.

Now, there is some controversy about the proposal — especially by those who do serious graphics stuff. Does the C++ standard library need 2D graphics? Shouldn’t the committee focus on real issues instead of some toy library that is never going to be used for serious applications?

But I’m not here to rant about the stupid standard committee and the completely bloated and unusable standard library, like some do. Instead, this discussion got me thinking: What should be part of a language’s standard library?

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Author's profile picture Jonathan

Write explicit constructors - but what about assignment?

Implicit conversions considered harmful.

Okay, this might be a little harsh:

Potentially dangerous and/or expensive implicit conversions considered harmful.


Implicit conversions will happen “accidentally” by their very nature, so if they happen, they should always do the right thing.

And how to prevent implicit conversions? Simple: use an explicit constructor.

But that’s only half of the problem: What about assignment? Is there explicit assignment? If so, when do I use it?

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Author's profile picture Jonathan