Beyond struct: Meta-programming a struct Replacement in C++20 - John Bandela - CppCon 2021

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The humble struct. We all use it. We all bump up against its limitations, especially when trying to manipulate it at compile time.
What if I told you that C++20 has enough features that we can meta-program a struct replacement?
Want to have static, compile-time introspection?
Want to add and remove members with compile-time programming?
Want to have type deduction for members?
Want to easily convert from array of structures to structure of arrays (SOA) to optimize cache-friendly traversal?
C++20 allows us to do all these things and more!
No preprocessors, no macros, just standard C++.
Come join me as we explore the magic unleashed by C++20!
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John Bandela
I first started programming in C++ at age 14 in 1994 when I cajoled my parents into buying me Visual C++ 1.0 for my birthday. It took a while, but as I learned the language, I decided I really liked C++. I attended the University of Florida and obtained my undergraduate degree in Computer and Information Science. During my undergraduate time, I created and submitted Boost.Tokenizer. I went on to medical school and neurosurgery residency, but decided to do something with a little less scary undefined behavior and returned to programming in C++.
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[@MaitreBart]

It's very interesting on paper (i.e. in a code review). It's full of good ideas. Such code is relatively easy to use and to review. But I'm a pragmatic developer. And in the debugger, that's a whole other story. If the meta_struct is composed of 2 iterators to a deque and 1 bool, and a function returns such an object, finding the value of the bool member in gdb is challenging.

[@JohnDlugosz]

You know, the variable layout of the fields in a structure, as well as automatic AOS to SOA was a fundamental feature of the JOVIAL language. That was in 1958, making it, along with ALGOL itself, one of the first block-structured languages. This particular feature did not catch on and as far as I know was not part of any other major language on the ALGOL family tree.

[@N....]

34:00 That is actually really cool, I guess since the caller does the matching it's as efficient at runtime as having three reference parameters right? EDIT: Actually I think this can be done with minimal compile overhead and regular structs if person_ref has a template constructor

[@Ken-S]

This talk showed a need for dynamic declaration for a type. I think cpp have to consider support "compiler time struct / class" and a way to convert them to "type / template".

[@petermuller608]

Great talk! However, the pointer highlighting is highly distracting due to low frame rate

[@Solarbonite]

It'd be kinda nice to add operator[] for get. I think it should be doable and could make it look more standard? Eg person.id vs person["id"]? Kinda like how lua tables allow . indexing and array indexing.

[@VivekNa]

The field name is a template param. So you can't get that array syntax

[@kamlot0]

I think it is impossible. For get to work you need to know the value of the string at compile time, therefore it has to be inside . person["id"] is equivalent to get("id", person). But it needs to be get(person).

[@YariRu]

this is crazy

[@ratgr]

He asked himself if he could do it never if he should, hahah, amazing metaprograming skill however I woudn't use it, because of compiletime

[@budiardjo6610]

i'm cry

[@saeed6296]

I wish there is an explanation for this complicated and ugly syntax 😭

[@dozerthecat]

C++ gets more academic every update. It's sad. We use c++ for the performance. Stop trying to draw analogies to json parsing. You are killing the language.

[@TheIgoorR]

If you know C++ good, you can boost your code performance! This is true reason

[@nickwilson3499]

@@TheIgoorR All of c++'s features, yet it's still slower than plain C

[@broken_abi6973]

@@nickwilson3499 no, it is not.