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0 pointshyperbrainer1y ago0 comments

Okay this is really funny because I was messing about with generics relating to the Write trait just yesterday, leading to much frustration.

> you find yourself propagating a generic bound up an entire hierarchy of data structures and functions using those structures

And I did exactly that. I did eventually get around to using dyn Write, but that still gave me headaches because of how I cannot use impl Write as a result type in closures, which I need to do if I want to use tracing_subscriber::fmt::with_writer() and pass in these trait objects.

Despite being this close to the solution, I somehow again wound up propagating generics back at least four functions.

I ended up not writing any generic-based stuff and resigned to just manually writing each type's implementation out, but I am going to tinker with this again today. Hopefully, I can use your advice.

Thank you so much for taking the time to write this. Means a lot!

> there was something satisfying about C in the old DOS days, where you could make a pointer to video memory and scribble on it

Exactly.

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JoshTriplett1y ago· 2 in thread

> I did eventually get around to using dyn Write, but that still gave me headaches because of how I cannot use impl Write as a result type in closures,

I hope we manage to fix that! We're working on making `impl Trait` usable everywhere a type works. I'll check where "return type of a closure" is on the `impl Trait` radar.

https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lan...

> which I need to do if I want to use tracing_subscriber::fmt::with_writer() and pass in these trait objects.

Would https://docs.rs/tracing-subscriber/0.3.19/tracing_subscriber... help you?

> Thank you so much for taking the time to write this. Means a lot!

Thank you as well for taking the time to fill in more details!

structural1y ago

I was just looking for something very similar, this is neat!

I think even moreso I can understand the sense of Rust feeling too large not because the language itself is, but because there are SO many of these neat tricks and little utility functions that are necessary to express what you want, and it's quite impossible to remember each and every one and how to go back and find them later.

hyperbrainerOP1y ago

Wow, thank you so much for taking the time to do this. I love all of you guys in the rust community.

> Would https://docs.rs/tracing-subscriber/0.3.19/tracing_subscriber... help you?

Indeed. This is brilliant.

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