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New lint: Prefer mem::take over Vec::split_off(0) #4953

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tesuji opened this issue Dec 25, 2019 · 4 comments · May be fixed by #14814
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New lint: Prefer mem::take over Vec::split_off(0) #4953

tesuji opened this issue Dec 25, 2019 · 4 comments · May be fixed by #14814
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@andre-digiexam
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A-lint Area: New lints good-first-issue These issues are a good way to get started with Clippy S-needs-discussion Status: Needs further discussion before merging or work can be started

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@tesuji
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tesuji commented Dec 25, 2019 •
edited by rustbot
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let mut vec = vec![1,2,3];
let vec2 = vec.split_off(0);

Should be written as

let vec2  = std::mem::take(&mut vec);
@tesuji
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tesuji commented Dec 25, 2019 •
edited
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Oh, wait. The semantics between two functions are different.
Vec::split_off leave the caller with same capacity while mem::take leave call with default value
(in this case an empty Vec).

@basil-cow
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I think vec.drain(..).collect() better represents the intention behind vec.split_off(0) (assuming it doesn't change capacity, which I don't think it is but seems like it's not specified either).

@camsteffen camsteffen added good-first-issue These issues are a good way to get started with Clippy A-lint Area: New lints S-needs-discussion Status: Needs further discussion before merging or work can be started labels Jan 26, 2021
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@sebhernandezr sebhernandezr linked a pull request May 15, 2025 that will close this issue
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A-lint Area: New lints good-first-issue These issues are a good way to get started with Clippy S-needs-discussion Status: Needs further discussion before merging or work can be started
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WIP: add unnecessary_split_off lint sebhernandezr/rust-clippy
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@camsteffen @tesuji @Zalathar @basil-cow @andre-digiexam