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Simplify the exhaustiveness check and add comments

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Jakub Wieczorek 2012-12-15 23:11:58 +00:00 committed by Graydon Hoare
parent 856dbac567
commit 1fdfd3b1d6
1 changed files with 37 additions and 37 deletions
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74
src/librustc/middle/check_alt.rs
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@ -392,49 +392,49 @@ fn missing_ctor(cx: @AltCheckCtxt,
else { Some(val(const_bool(true))) }
}
ty::ty_unboxed_vec(*) | ty::ty_evec(*) => {
let max_len = do m.foldr(0) |r, max_len| {
match r[0].node {
pat_vec(elems, _) => uint::max(elems.len(), max_len),
_ => max_len
}
};
let min_len_with_tail = do m.foldr(max_len + 1) |r, min_len| {
match r[0].node {
pat_vec(elems, tail) => {
if tail.is_some() && elems.len() < min_len {
elems.len()
} else {
min_len
}
}
_ => min_len
}
};
let vec_lens = do m.filter_map |r| {
match r[0].node {
pat_vec(elems, tail) => {
match tail {
None if elems.len() < min_len_with_tail => Some(elems.len()),
// Find the lengths and tails of all vector patterns.
let vec_pat_lens = do m.filter_map |r| {
match r[0].node {
pat_vec(elems, tail) => {
Some((elems.len(), tail.is_some()))
}
_ => None
}
}
_ => None
}
};
let mut sorted_vec_lens = do sort::merge_sort(vec_lens) |a, b| {
a < b
};
// Sort them by length such that for patterns of the same length,
// those with a destructured tail come first.
let mut sorted_vec_lens = sort::merge_sort(vec_pat_lens,
|&(len1, tail1), &(len2, tail2)| {
if len1 == len2 {
tail1 > tail2
} else {
len1 <= len2
}
}
);
vec::dedup(&mut sorted_vec_lens);
let mut found_tail = false;
let mut next = 0;
let mut missing = None;
for uint::range(0, min_len_with_tail) |i| {
if i >= sorted_vec_lens.len() || i != sorted_vec_lens[i] {
missing = Some(i);
break;
}
};
if missing.is_none() && min_len_with_tail > max_len {
missing = Some(min_len_with_tail);
for sorted_vec_lens.each |&(length, tail)| {
if length != next {
missing = Some(next);
break;
}
if tail {
found_tail = true;
break;
}
next += 1;
}
// We found patterns of all lengths within <0, next), yet there was no
// pattern with a tail - therefore, we report vec(next) as missing.
if !found_tail {
missing = Some(next);
}
match missing {
Some(k) => Some(vec(k)),