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perf: presize result slice in getChildrenWithSiblingType #567

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perf: presize result slice in getChildrenWithSiblingType #567

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14 changes: 14 additions & 0 deletions traversal.go
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Original file line number Diff line number Diff line change
Expand Up @@ -657,6 +657,20 @@ func getChildrenWithSiblingType(parent *html.Node, st siblingType, skipNode *htm
}
}

// For the cases that collect every matching sibling, count them in a
// cheap pointer walk first so the result slice can be sized exactly,
// avoiding repeated slice growth. The Until cases are skipped (counting
// would require running the predicate twice) and so are the single-result
// Next/Prev cases.
switch st {
case siblingAll, siblingAllIncludingNonElements, siblingPrevAll, siblingNextAll:
n := 0
for c := iter(nil); c != nil; c = iter(c) {
n++
}
result = make([]*html.Node, 0, n)
}

for c := iter(nil); c != nil; c = iter(c) {
// If this is an ...Until case, test before append (returns true
// if the until condition is reached)
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