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Improve performance of seq/map peeks #1206

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merged 3 commits into from
Oct 19, 2024
Merged

Improve performance of seq/map peeks #1206

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2a4cb44
Rearrange 'match peek'
dtolnay Oct 19, 2024
0f54a1a
Handle early return sooner on eof in seq or map
dtolnay Oct 19, 2024
f2082d2
Clearer order of comparisons
dtolnay Oct 19, 2024
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74 changes: 35 additions & 39 deletions src/de.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1930,30 +1930,26 @@ impl<'de, 'a, R: Read<'de> + 'a> de::SeqAccess<'de> for SeqAccess<'a, R> {
seq: &mut SeqAccess<'a, R>,
) -> Result<bool> {
let peek = match tri!(seq.de.parse_whitespace()) {
Some(b']') => {
return Ok(false);
}
Some(b',') if !seq.first => {
seq.de.eat_char();
tri!(seq.de.parse_whitespace())
}
Some(b) => {
if seq.first {
seq.first = false;
Some(b)
} else {
return Err(seq.de.peek_error(ErrorCode::ExpectedListCommaOrEnd));
}
}
Some(b) => b,
None => {
return Err(seq.de.peek_error(ErrorCode::EofWhileParsingList));
}
};

match peek {
Some(b']') => Err(seq.de.peek_error(ErrorCode::TrailingComma)),
Some(_) => Ok(true),
None => Err(seq.de.peek_error(ErrorCode::EofWhileParsingValue)),
if peek == b']' {
Ok(false)
} else if seq.first {
seq.first = false;
Ok(true)
} else if peek == b',' {
seq.de.eat_char();
match tri!(seq.de.parse_whitespace()) {
Some(b']') => Err(seq.de.peek_error(ErrorCode::TrailingComma)),
Some(_) => Ok(true),
None => Err(seq.de.peek_error(ErrorCode::EofWhileParsingValue)),
}
} else {
Err(seq.de.peek_error(ErrorCode::ExpectedListCommaOrEnd))
}
}

Expand Down Expand Up @@ -1985,31 +1981,31 @@ impl<'de, 'a, R: Read<'de> + 'a> de::MapAccess<'de> for MapAccess<'a, R> {
{
fn has_next_key<'de, 'a, R: Read<'de> + 'a>(map: &mut MapAccess<'a, R>) -> Result<bool> {
let peek = match tri!(map.de.parse_whitespace()) {
Some(b'}') => {
return Ok(false);
}
Some(b',') if !map.first => {
map.de.eat_char();
tri!(map.de.parse_whitespace())
}
Some(b) => {
if map.first {
map.first = false;
Some(b)
} else {
return Err(map.de.peek_error(ErrorCode::ExpectedObjectCommaOrEnd));
}
}
Some(b) => b,
None => {
return Err(map.de.peek_error(ErrorCode::EofWhileParsingObject));
}
};

match peek {
Some(b'"') => Ok(true),
Some(b'}') => Err(map.de.peek_error(ErrorCode::TrailingComma)),
Some(_) => Err(map.de.peek_error(ErrorCode::KeyMustBeAString)),
None => Err(map.de.peek_error(ErrorCode::EofWhileParsingValue)),
if peek == b'}' {
Ok(false)
} else if map.first {
map.first = false;
if peek == b'"' {
Ok(true)
} else {
Err(map.de.peek_error(ErrorCode::KeyMustBeAString))
}
} else if peek == b',' {
map.de.eat_char();
match tri!(map.de.parse_whitespace()) {
Some(b'"') => Ok(true),
Some(b'}') => Err(map.de.peek_error(ErrorCode::TrailingComma)),
Some(_) => Err(map.de.peek_error(ErrorCode::KeyMustBeAString)),
None => Err(map.de.peek_error(ErrorCode::EofWhileParsingValue)),
}
} else {
Err(map.de.peek_error(ErrorCode::ExpectedObjectCommaOrEnd))
}
}

Expand Down