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I am trying to match on a Rust Option<Component>. Component is this enum doc.rust-lang.org/std/path/struc What should go where the ... goes here? It isn't allowing _, it says _ must be on "the left". Some ML-likes let you do something like Some(Normal(_) as x) but it didn't like that

match componentOption {
Some(component) if component == Component::Normal(...) => { depth += 1; filename.push(component); }

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fun alex

@myrrlyn

Mar 2, 2021

the specific reason this doesn't work is that you have found the only part of pattern matching that /isn't/ a pattern; that needs to be a const-expression that constructs a value, since any bound names in the pattern left of the "if" are getting their values compared on the right

mcc

@mcclure111

Mar 2, 2021

Out of curiosity is there a reason ocaml style "as" COULDN'T have been the syntax here (where Rust uses @)? I actually tried that first lol Also is @ allowed anywhere outside destructurings? Can I use it in let destructures?

fun alex

@myrrlyn

Mar 2, 2021

- /probably/ just limiting how many overloads the word has? the @ sigil also used to do more things, and we used to have more sigils, but *now* it's vestigial and weird - yeah that should work, though it'd be heavily constrained by reference rules to prevent partial invalidation