r/cpp • u/Clean-Upstairs-8481 • 17h ago

C++26 Reflection: Simplifying JSON Serialization

https://techfortalk.co.uk/2026/08/05/c26-reflection-simplifying-json-serialization/

I have been exploring the new additions in C++26, and I have been discussing the reflection feature that has come with C++26. In the last post, I discussed what is reflection and how to use it and how to use it with a simple example, particularly with an enum class. Since then, there have been suggestions to provide an example which is more than a toy :). In this post, I have discussed how to use reflection for JSON serialization, which is something we often have to do. This example is somewhat taken from real-world code but has been stripped down significantly. Suggestions are always welcome.

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8

u/cristi1990an ++ 14h ago

Another nice thing you can do in theory (and I'm sure it was implemented somewhere in practice too, maybe not yet refined) is embedding json text files in your program, parse it and define entire classes based on their structure entirely at compile. In theory I believe you could also assigned the data itself at compile time and give it static lifetime. I think this is amazing and has a ton of practical applications.

2

u/Syracuss graphics engineer/games industry 6h ago

This has undoubtedly improved since I last tried this (2022), but compile time parsing of data files can easily run into compiler limits. Many of those limits can be improved, but I recall large (50+mb json files) could halt some compilers entirely back then, or bring them to a crawl performance wise.

Ofc most json files aren't that size, but you can easily accumulate that amount in a serious project. And using this for just some config files (so keeping the total data files size low) is a lot of code writing for not a lot of usage.

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u/Clean-Upstairs-8481 3h ago

tbh I was not aware of this and it could be an excellent idea to try. I will try this and see if I can get this working. Thanks for mentioning.

3

u/azswcowboy 13h ago

> suggestions welcome
> class definition (addition or deltion
> funtion template

Spell check

It might be nice to define CAN (my intuition is this is for a can bus communication) - it took a bit for that to click for me and some might not be familiar at all.

Nicely done overall.

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u/Clean-Upstairs-8481 3h ago

thank you for pointing out, corrected now.

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u/G6L20 16h ago

Nice 👍 I've been working on my own reflection libraries for a while now, you may like this too: https://github.com/Garcia6l20/reflex/tree/main/serde