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Today I learned you can exhaustively pattern match in argument positions in Rust.

384

Esteban K�ber –

@ekuber

Mar 5

(for the audience) That's because fn params, let bindings and match arm patterns are all patterns.

bibimbytes

@uint128_t

Mar 5

Can you redefine a method with different patterns and rust dispatches to the right one?

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@eddyb_r

Mar 5

the patterns are effectively part of the body *not* the signature in the example here, it's like if you had fn register(arg0: Json<Register>) { let Json(data) = arg0; dbg!(data); } so there's no way a pattern like that can influence something elsewhere in the code

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@eddyb_r

Mar 5

oh, wait, are you referring to the functional style of defining functions piecemeal? this isn't valid Rust but I guess it *theoretically* could one day be: fn foo(_: Option<u32>) -> u32; fn foo(None) = 123; fn foo(Some(x)) = x; but that'd be sugar for a `match` *inside* `foo`

Replying to

IIRC there was a proposal back in the day for something like: fn foo(_: Option<u32>) -> u32 match { None => 123, Some(x) => x, } Would reduce a level of indentation at least. …but maybe I am misremembering. 😵‍💫

2:10 AM · Mar 6, 2022Twitter Web App

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