[CogDisco]

Why not have controls in your program to do these immediate, non-logic changing modifications? It can report the ideal value through a debug interface. No recompiles needed.

I'd also recommend getting used to serialisation/deserialisation. Serde for Rust makes this remarkably easy. Writing every setting to a file is simple if the compiler can do it for you, rather than you walking the long way around.

[logimame]

When you're doing any sort of non-trivial gamedev, graphics, or physics simulation work, there are so many instances when you have to get a bunch of magic numbers by trial and error, and it's usually all over your code. If you try to "refactor" these cleanly into a separate JSON file (hint: it NEVER is that clean), it still takes time and effort away from you to by writing boilerplate code, which seriously kills your momentum for experimenting and iterating with your code. It's kind of a niche domain-specific thing which most gamedevs and graphics programmers would sympathize with.

Also there are also a shit-ton of minor logic-changing modifications when you're writing prototype gamedev code, (for example, moving an if statement here or there to tweak the physics of your platforming). These cannot be easily represented in config files, and this is why people attach lightweight scripting languages like Lua to their game engines (so that you don't have to wait for those atrocious C++ compile times when tweaking your gameplay code).

(Ironically, serde is known for its atrocious compile times, which really makes the situation even worse. Because of this some frustrated Rust gamedevs wrote their own serialization libraries such as nanoserde (https://github.com/not-fl3/nanoserde)... but you get the point.)