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Speed up String::from_utf16 #55530

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Nov 15, 2018
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Speed up String::from_utf16 #55530

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10 changes: 9 additions & 1 deletion src/liballoc/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -618,7 +618,15 @@ impl String {
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
let mut ret = String::with_capacity(v.len());
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for c in decode_utf16(v.iter().cloned()) {
if let Ok(c) = c {
ret.push(c);
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Would be nice to have a comment explaining why the code works this way instead of the more "obvious" collect call.

Basically, what you wrote in the PR should be in the code.

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Good idea; since it is already rolled up, I can add this comment afterwards, along with some other assorted code adjustments.

} else {
return Err(FromUtf16Error(()));
}
}
Ok(ret)
}

/// Decode a UTF-16 encoded slice `v` into a `String`, replacing
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