From 08f17b35385f13148dcebc7f0335a80df7da4a65 Mon Sep 17 00:00:00 2001
From: Vildan Safin <you@example.com>
Date: Mon, 30 Mar 2026 16:19:46 +0500
Subject: [PATCH] perf(chunk): Remove if from chunk bounds

---
 benchmark/core_slice_bench_test.go | 64 ++++++++++++++++++++++++++++++
 slice.go                           | 35 ++++++++++------
 2 files changed, 86 insertions(+), 13 deletions(-)

diff --git a/benchmark/core_slice_bench_test.go b/benchmark/core_slice_bench_test.go
index 2df8b6958..c7ff3c354 100644
--- a/benchmark/core_slice_bench_test.go
+++ b/benchmark/core_slice_bench_test.go
@@ -1013,3 +1013,67 @@ func BenchmarkFromSlicePtrOr(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkChunkIntSmallDataSmallChunk(b *testing.B) {
+	data := genSliceInt(100)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 3)
+	}
+}
+
+func BenchmarkChunkIntSmallDataLargeChunk(b *testing.B) {
+	data := genSliceInt(100)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 50)
+	}
+}
+
+func BenchmarkChunkIntMediumDataSmallChunk(b *testing.B) {
+	data := genSliceInt(10_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 7)
+	}
+}
+
+func BenchmarkChunkIntMediumDataLargeChunk(b *testing.B) {
+	data := genSliceInt(10_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 1024)
+	}
+}
+
+func BenchmarkChunkIntLargeDataSmallChunk(b *testing.B) {
+	data := genSliceInt(1_000_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 13)
+	}
+}
+
+func BenchmarkChunkIntLargeDataLargeChunk(b *testing.B) {
+	data := genSliceInt(1_000_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 8192)
+	}
+}
+
+func BenchmarkChunkStringMediumDataSmallChunk(b *testing.B) {
+	data := genSliceString(10_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 7)
+	}
+}
+
+func BenchmarkChunkStringMediumDataLargeChunk(b *testing.B) {
+	data := genSliceString(10_000)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 1024)
+	}
+}
diff --git a/slice.go b/slice.go
index 08522cdb2..6d599b0d7 100644
--- a/slice.go
+++ b/slice.go
@@ -351,30 +351,39 @@ func GroupByMapErr[T any, K comparable, V any](collection []T, transform func(it
 // Chunk returns a slice of elements split into groups of length size. If the slice can't be split evenly,
 // the final chunk will be the remaining elements.
 // Play: https://go.dev/play/p/kEMkFbdu85g
+// Chunk returns a slice of elements split into groups of length size.
+// If the slice can't be split evenly, the final chunk will be the remaining elements.
+// Copy chunk in a new slice, to prevent memory leak and free memory from initial collection.
+// Play: https://go.dev/play/p/kEMkFbdu85g
 func Chunk[T any, Slice ~[]T](collection Slice, size int) []Slice {
 	if size <= 0 {
 		panic("lo.Chunk: size must be greater than 0")
 	}
 
-	chunksNum := len(collection) / size
-	if len(collection)%size != 0 {
-		chunksNum++
+	if len(collection) == 0 {
+		return []Slice{}
 	}
 
-	result := make([]Slice, 0, chunksNum)
+	// Reason: https://github.com/golang/go/issues/77287
+	clone := func(s Slice) Slice {
+		dst := make(Slice, len(s))
+		copy(dst, s)
+		return dst
+	}
 
-	for i := 0; i < chunksNum; i++ {
-		last := (i + 1) * size
-		if last > len(collection) {
-			last = len(collection)
-		}
+	chunksNum := (len(collection) + size - 1) / size
+	result := make([]Slice, chunksNum)
 
-		// Copy chunk in a new slice, to prevent memory leak and free memory from initial collection.
-		newSlice := make(Slice, last-i*size)
-		copy(newSlice, collection[i*size:last])
-		result = append(result, newSlice)
+	// Process all full-sized chunks
+	i := 0
+	for ; i < chunksNum-1; i++ {
+		pos := i * size
+		result[i] = clone(collection[pos : pos+size])
 	}
 
+	// Handle the final chunk (may be smaller than size)
+	result[chunksNum-1] = clone(collection[i*size:])
+
 	return result
 }