A Journey Into Non-Virtual Polymorphism in C++ - Rudyard Merriam - CppCon 2023

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A Journey Into Non-Virtual Polymorphism addressing std::any, std::variant and visit, std::tuple and apply, and CRTP. - Rudyard Merriam - CppCon 2023
github.com/CppCon/CppCon2023
Join me on an introductory journey into polymorphism that doesn't use class inheritance and virtual functions. I'll share my amazement at how polymorphism permeates C++. Then we'll visit the long-used Curiously Recurring Template Pattern (CRTP) with its modernization using implicit this.
Do you like lambdas? So does the override pattern, which uses them to handle std::tuples and std::variants with std::apply and std::visit.
Want to walk through a container of disparate types invoking their functions? You'll see this and all the above in code examples galore.
Afterward, you'll be eager to learn more on your own!
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Rudyard Merriam
Rud Merriam is a retired software developer, having lived through the spaghetti, structured programming, and object-oriented development paradigms. He's trying to figure out functional programming and keep up with the latest C++ standards.
Rud wrote his first FORTRAN IV in 1968 and his first C++ in 1990 with Borland's Turbo C++. During his career, he worked mainly with embedded systems, with one system measuring the flow in real pipelines. Since retirement, he has used C++ with multiple NASA Centennial Challenges of robotics on Mars and the Moon. He sporadically writes about C++ on Medium.com.
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[@wojciechbartczak3109]

I love this talk, it is true gem. Old school, straight to the implementation. No BS 😀Loaded with knowledge and experience. Extra thing added, it considers embedded or more restricted environments. Loop unrolling through std::apply() is wild!

[@ChrisCarlos64]

I found some if this very insightful and helpful. I hadn't used std::any, std::variant, or any of the tools with them, but learning this has opened my eyes to trying them out later so I can remember them and hopefully keep in mind when and where to use them when applicable.

[@Radioguy00]

Well done presentation. Examples are simple and clear

[@hsarasan]

Beautiful presentation. Such great examples

[@stanbarvinsky1011]

I've been using std::variant for some time and found it extremely useful (as a type safe union or using it in a visitor). Along with optional this is best feature in C++17 IMO. I also implemented a number of classes similar to what std::any does but with some additional features and type constrains, but I am yet to find a use case for std::any itself.

[@makaedg]

Agree, C++17 gave us so much elements from functional programming. I also really like to use fold expressions. C++ is awesome

[@mfc1190]

I haven’t used std::variant before, but I use std::optional sometimes when it’s appropriate, I’d like to check this out!

[@pawello87]

'Deducing this' with CRTP is sooo neat!

[@eric-seastrand]

Hi Rud! I remember you from a meet-up group years ago. Glad to see you’re doing well. Cheers!

[@samuelsrikar2870]

Amazing talk. Loved it :D

[@commander7023]

This is a great talk by him. Concise and solid communication

[@niteshkumarsukumaran]

Really good talk! Love to try these :)

[@KartikayKaul]

We were taught cpp in 11th and 12th grade in turbo cpp. XD i recognise this screenshot very well.

[@multiHappyHacker]

Pretty good talk so far, I have played with a lot of these things in my personal projects already. I guess std::function would qualify as runtime polymorphism though, the templates are the static (compile time) version.

[@jfsimon1981]

If there's a library with this style for embedded i'd love get a look at it. Looks awesome and clean. Regards Jean-François

[@johnwellbelove148]

My OSS library may be useful to you. It has many STL features, but uses no dynamically allocated memory. I've been maintaining it since 2014. Search 'Embedded Template Library'

[@marcoradovancovici1312]

Cool stuff!

[@user-gc5vf7un7e]

Nice talk. I just want to provide a little correction: the CTAD line is needed prior to C++17, not C++20.( 21:26 )

[@stephenjames2951]

Like his every man style. Credibility from the trenches.

[@MartinCordova]

What a good way to express it

[@RudMerriam]

Thanks! I didn't realize it, but that is exactly how I wanted it to sound. "Shucks, I'm just another developer talking about m' code."

[@lombeelo8780]

Nice one. Sad to see no comments here.

[@junaid1464]

I'm way younger, but turbo c++ was my first editor

[@raymitchell9736]

This is something I run into quite a lot, so I need to see if this will work for me. I too do embedded systems and the compilers are not as up to date as we'd like, Arduino is, if I recall correctly, C++ 14 and I need to do something like this for a hobby project so it's more than a good example in my case. And I ran into all kinds of weirdness, it seems that if you're having to force the language to abstract an interface, that perhaps that language isn't yet expressive enough to handle it, I would like dynamic polymorphic dispatch... that's true Object Oriented.

[@johnwellbelove148]

My OSS library may be useful to you. It has many STL features, but uses no dynamically allocated memory. I've been maintaining it since 2014. Search 'Embedded Template Library'

[@drescherjm]

1:45 I spent thousands of hours using that IDE.

[@protasov-by]

Same things I thought about last week 😂

[@randfur]

35:50 for code.

[@CartoType]

Interesting but I can’t see the reason for not using virtual functions.

[@randomname-cc9hc]

Virtual functions require virtual table, which increases size of every single object of given class. Also, calls of such functions are slower, because instead of straightforward functon call we need to look up into vtable and only then call suitable implementation. This is negligible for most cases, but for embedded systems or other constrained enviroments such solution can significantly improve perfomance of program

[@imrank340]

This old-Timer saying something about C++ programming but I cant figure out where IS start and where is an End? Bit hard to understand.

[@josefpharma4714]

From a C++ experimental perspective: Nice. From real coding perspective: Too complex for nearly nothing. 😀

[@toolazytobeoriginal4587]

Wait so is it too complex for basically any project or is it simple enough for basically anything?

[@makaedg]

I used CRTP in the production code this week.

[@andrewf8366]

There are plenty of times that this kind of polymorphism is massively simpler than alternatives.

[@StanleyPinchak]

Deducing This is going to be a game changer for currying and mixins. I use std::variant + overload in my own production code and I am excited to see the static polymorphism capabilities of C++23 reduce both boilerplate and cognitive load. This will lead to much greater acceptance of these tools in community.

[@josefpharma4714]

@@toolazytobeoriginal4587 I would not use it in real projects. IMHO: Code should be optimized for easy reading. Many years ago when I went through the C++ Standard (2003) I liked coding C++ on its boundaries and find the most clever (I thought at this time) solutions. But this is not easy to read - you could say it’s a skill issue, but you need to assume typically skilled c++ developers. And most of them are not even familiar with e.g. template specialization - specially in embedded.