[slashdev]

Are you saying there aren’t any legitimate uses for runtime reflection? Because I think Java and .Net, even Go have proved that wrong over the years.

This seems like a valuable library. It’s impressive that it can be so powerful in a compiled language. C and C++ are much older but don’t have anything quite like this.

[saghm]

A lot of what you'd use reflection for in GC languages is done with macros/code generation at compile time in Rust. For example, rather than using reflection to map objects to something like JSON to serialize, Rust has a library called serde (https://serde.rs/) that lets you annotate structs and enums and generate conversions at compile time that you can use. I wouldn't go so far as saying that there's no possible legitimate use of reflection, but I do wonder how much could be happening in Java and C# and Go that's so dynamic that you wouldn't be able to reason about it in advance. I think most of what reflection is used for in those languages _could_ be done at compile time, but it would both require a way to express it (via macros, codegen, or something like that) and be worth the extra compile time in order to save runtime. Rust's ethos is to try to optimize as much as possible for runtime efficiency even at the expensive of compile time, and while there can be (and often are!) ways to opt out of this for a given feature, it's almost never the default.

[slashdev]

I’ve used Rust extensively the last couple years. I understand that. A lot of what people do with reflection in Go could be done more efficiently with code generation - but more easily with reflection. I’m sure the same is true in Rust, to a lesser extent. There are times when runtime reflection would be really nice to have.