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Related issue: #20
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,103 @@ | ||
| use std::{borrow::Borrow, fmt::Display, ops::Deref, str::from_utf8}; | ||
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| // Largest CowStr variant is Owned(String). A String uses 3 words of memory, but a fourth word is | ||
| // needed to hold the tag (the tag takes a byte, but a full word is used for alignment reasons.) | ||
| // This means that the available space we have for an inline string is 4 words - 1 byte for the tag | ||
| // and 1 word for encoding the length. | ||
| const MAX_INLINE_STR_LEN: usize = 4 * std::mem::size_of::<usize>() - 2; | ||
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| #[derive(Debug)] | ||
| pub enum CowStr<'s> { | ||
| Owned(String), | ||
| Borrowed(&'s str), | ||
| Inlined([u8; MAX_INLINE_STR_LEN], u8), | ||
| } | ||
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| impl<'s> CowStr<'s> { | ||
| pub fn take_borrowed(self) -> &'s str { | ||
| match self { | ||
| CowStr::Borrowed(s) => s, | ||
| CowStr::Owned(_) | CowStr::Inlined(..) => panic!(), | ||
| } | ||
| } | ||
| } | ||
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| impl<'s> Deref for CowStr<'s> { | ||
| type Target = str; | ||
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| fn deref(&self) -> &Self::Target { | ||
| match *self { | ||
| Self::Owned(ref s) => s.borrow(), | ||
| Self::Borrowed(s) => s, | ||
| // NOTE: Inlined strings can only be constructed from strings or chars, which means they | ||
| // are guaranteed to be valid UTF-8. We could consider unchecked conversion as well, but | ||
| // a benchmark should be done before introducing unsafes. | ||
| Self::Inlined(ref inner, len) => from_utf8(&inner[..len as usize]).unwrap(), | ||
| } | ||
| } | ||
| } | ||
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| impl<'s> AsRef<str> for CowStr<'s> { | ||
| fn as_ref(&self) -> &str { | ||
| self.deref() | ||
| } | ||
| } | ||
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| impl<'s> From<char> for CowStr<'s> { | ||
| fn from(value: char) -> Self { | ||
| let mut inner = [0u8; MAX_INLINE_STR_LEN]; | ||
| value.encode_utf8(&mut inner); | ||
| CowStr::Inlined(inner, value.len_utf8() as u8) | ||
| } | ||
| } | ||
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| impl<'s> From<&'s str> for CowStr<'s> { | ||
| fn from(value: &'s str) -> Self { | ||
| CowStr::Borrowed(value) | ||
| } | ||
| } | ||
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| impl<'s> From<String> for CowStr<'s> { | ||
| fn from(value: String) -> Self { | ||
| CowStr::Owned(value) | ||
| } | ||
| } | ||
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| impl<'s> Clone for CowStr<'s> { | ||
| fn clone(&self) -> Self { | ||
| match self { | ||
| CowStr::Owned(s) => { | ||
| let len = s.len(); | ||
| if len > MAX_INLINE_STR_LEN { | ||
| CowStr::Owned(s.clone()) | ||
| } else { | ||
| let mut inner = [0u8; MAX_INLINE_STR_LEN]; | ||
| inner[..len].copy_from_slice(s.as_bytes()); | ||
| CowStr::Inlined(inner, len as u8) | ||
| } | ||
| } | ||
| CowStr::Borrowed(s) => CowStr::Borrowed(s), | ||
| CowStr::Inlined(inner, len) => CowStr::Inlined(*inner, *len), | ||
| } | ||
| } | ||
| } | ||
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| impl<'s> PartialEq for CowStr<'s> { | ||
| fn eq(&self, other: &Self) -> bool { | ||
| self.deref() == other.deref() | ||
| } | ||
| } | ||
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| impl<'s> Eq for CowStr<'s> {} | ||
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| impl<'s> Display for CowStr<'s> { | ||
| fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { | ||
| f.write_str(self.deref()) | ||
| } | ||
| } | ||
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| impl<'s, 'a> FromIterator<&'a str> for CowStr<'s> { | ||
| fn from_iter<T: IntoIterator<Item = &'a str>>(iter: T) -> Self { | ||
| CowStr::Owned(FromIterator::from_iter(iter)) | ||
| } | ||
| } |