1 files changed, 148 insertions, 0 deletions
diff --git a/src/bytes/iter.go b/src/bytes/iter.go
new file mode 100644
index 0000000000..1cf13a94ec
--- /dev/null
+++ b/src/bytes/iter.go
@@ -0,0 +1,148 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package bytes
+
+import (
+	"iter"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Lines returns an iterator over the newline-terminated lines in the byte slice s.
+// The lines yielded by the iterator include their terminating newlines.
+// If s is empty, the iterator yields no lines at all.
+// If s does not end in a newline, the final yielded line will not end in a newline.
+// It returns a single-use iterator.
+func Lines(s []byte) iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		for len(s) > 0 {
+			var line []byte
+			if i := IndexByte(s, '\n'); i >= 0 {
+				line, s = s[:i+1], s[i+1:]
+			} else {
+				line, s = s, nil
+			}
+			if !yield(line[:len(line):len(line)]) {
+				return
+			}
+		}
+		return
+	}
+}
+
+// explodeSeq returns an iterator over the runes in s.
+func explodeSeq(s []byte) iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		for len(s) > 0 {
+			_, size := utf8.DecodeRune(s)
+			if !yield(s[:size:size]) {
+				return
+			}
+			s = s[size:]
+		}
+	}
+}
+
+// splitSeq is SplitSeq or SplitAfterSeq, configured by how many
+// bytes of sep to include in the results (none or all).
+func splitSeq(s, sep []byte, sepSave int) iter.Seq[[]byte] {
+	if len(sep) == 0 {
+		return explodeSeq(s)
+	}
+	return func(yield func([]byte) bool) {
+		for {
+			i := Index(s, sep)
+			if i < 0 {
+				break
+			}
+			frag := s[:i+sepSave]
+			if !yield(frag[:len(frag):len(frag)]) {
+				return
+			}
+			s = s[i+len(sep):]
+		}
+		yield(s[:len(s):len(s)])
+	}
+}
+
+// SplitSeq returns an iterator over all substrings of s separated by sep.
+// The iterator yields the same strings that would be returned by Split(s, sep),
+// but without constructing the slice.
+// It returns a single-use iterator.
+func SplitSeq(s, sep []byte) iter.Seq[[]byte] {
+	return splitSeq(s, sep, 0)
+}
+
+// SplitAfterSeq returns an iterator over substrings of s split after each instance of sep.
+// The iterator yields the same strings that would be returned by SplitAfter(s, sep),
+// but without constructing the slice.
+// It returns a single-use iterator.
+func SplitAfterSeq(s, sep []byte) iter.Seq[[]byte] {
+	return splitSeq(s, sep, len(sep))
+}
+
+// FieldsSeq returns an iterator over substrings of s split around runs of
+// whitespace characters, as defined by unicode.IsSpace.
+// The iterator yields the same strings that would be returned by Fields(s),
+// but without constructing the slice.
+func FieldsSeq(s []byte) iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		start := -1
+		for i := 0; i < len(s); {
+			size := 1
+			r := rune(s[i])
+			isSpace := asciiSpace[s[i]] != 0
+			if r >= utf8.RuneSelf {
+				r, size = utf8.DecodeRune(s[i:])
+				isSpace = unicode.IsSpace(r)
+			}
+			if isSpace {
+				if start >= 0 {
+					if !yield(s[start:i:i]) {
+						return
+					}
+					start = -1
+				}
+			} else if start < 0 {
+				start = i
+			}
+			i += size
+		}
+		if start >= 0 {
+			yield(s[start:len(s):len(s)])
+		}
+	}
+}
+
+// FieldsFuncSeq returns an iterator over substrings of s split around runs of
+// Unicode code points satisfying f(c).
+// The iterator yields the same strings that would be returned by FieldsFunc(s),
+// but without constructing the slice.
+func FieldsFuncSeq(s []byte, f func(rune) bool) iter.Seq[[]byte] {
+	return func(yield func([]byte) bool) {
+		start := -1
+		for i := 0; i < len(s); {
+			size := 1
+			r := rune(s[i])
+			if r >= utf8.RuneSelf {
+				r, size = utf8.DecodeRune(s[i:])
+			}
+			if f(r) {
+				if start >= 0 {
+					if !yield(s[start:i:i]) {
+						return
+					}
+					start = -1
+				}
+			} else if start < 0 {
+				start = i
+			}
+			i += size
+		}
+		if start >= 0 {
+			yield(s[start:len(s):len(s)])
+		}
+	}
+}