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Merged
merged 2 commits into from
Sep 12, 2016
Merged

Improve char_lit's readability and speed #36414

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4c274b6
Avoid an unnecessary intermediate value in char_lit().
nnethercote Sep 12, 2016
826f673
Lazily construct panic messages in char_lit().
nnethercote Sep 12, 2016
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35 changes: 16 additions & 19 deletions src/libsyntax/parse/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -287,29 +287,21 @@ pub fn char_lit(lit: &str) -> (char, isize) {
use std::char;

let mut chars = lit.chars();
let c = match (chars.next(), chars.next()) {
match (chars.next(), chars.next()) {
(Some(c), None) if c != '\\' => return (c, 1),
(Some('\\'), Some(c)) => match c {
'"' => Some('"'),
'n' => Some('\n'),
'r' => Some('\r'),
't' => Some('\t'),
'\\' => Some('\\'),
'\'' => Some('\''),
'0' => Some('\0'),
_ => { None }
'"' => return ('"', 2),
'n' => return ('\n', 2),
'r' => return ('\r', 2),
't' => return ('\t', 2),
'\\' => return ('\\', 2),
'\'' => return ('\'', 2),
'0' => return ('\0', 2),
_ => {}
},
_ => panic!("lexer accepted invalid char escape `{}`", lit)
};

match c {
Some(x) => return (x, 2),
None => { }
}

let msg = format!("lexer should have rejected a bad character escape {}", lit);
let msg2 = &msg[..];

fn esc(len: usize, lit: &str) -> Option<(char, isize)> {
u32::from_str_radix(&lit[2..len], 16).ok()
.and_then(char::from_u32)
Expand All @@ -318,7 +310,10 @@ pub fn char_lit(lit: &str) -> (char, isize) {

let unicode_escape = || -> Option<(char, isize)> {
if lit.as_bytes()[2] == b'{' {
let idx = lit.find('}').expect(msg2);
let idx = lit.find('}').unwrap_or_else(|| {
panic!("lexer should have rejected a bad character escape {}", lit)
});

let subslice = &lit[3..idx];
u32::from_str_radix(subslice, 16).ok()
.and_then(char::from_u32)
Expand All @@ -334,7 +329,9 @@ pub fn char_lit(lit: &str) -> (char, isize) {
'u' => unicode_escape(),
'U' => esc(10, lit),
_ => None,
}.expect(msg2);
}.unwrap_or_else(|| {
panic!("lexer should have rejected a bad character escape {}", lit)
})
}

/// Parse a string representing a string literal into its final form. Does
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