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As pointed out, the idiomatic way to do this is to use the try operator (`?`). But to answer your question about copies : Rust is a move-only language, copies

As pointed out, the idiomatic way to do this is to use the try operator (`?`). But to answer your question about copies : Rust is a move-only language, copies are actually called `.clone()`, except for a few types which are cheap enough to copy that they implement the `Copy` trait. So in the code you quoted, the match is done on the value of `result` (notice that there is not borrowing/`&` operator). The match arm `Err(err)` moves `err` out of `result` and returns it. Obviously, the compiler will optimize away all those moves, it's as if they did not exist.

littlestymaar 4y ago
> But to answer your question about copies : Rust is a move-only language, copies are actually called `.clone()`, except for a few types which are cheap enough to copy that they implement the `Copy` trait. This is almost true, but not exact. Copy is for everything where cloning is just memcopy, that doesn't means it's necessarily cheap ([42;4_000_000] implements Copy, yet it's not cheap to copy at all…). And moving things sometimes (but not always) means the thing is getting memcopied (or it could use a pointer, depending on the optimizer's m̶o̶o̶d̶ euristics)