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bytes, strings: align requirements for functions passed to FieldFuncs

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golang.org/cl/229763 removed the documentation of requirements of
the function passed to FieldsFunc. The current implementation does
not require functions to return consistent results but this had not
been the case for previous implementations.

Add the requirement for consistent results back to the documentation
to allow for future implementations to be more allocation efficient
for an output with more than 32 fields. This is possible with a two
pass algorithm first determining the number of fields used to allocate
the output slice and then splitting the input into fields.

While at it align the documentation of bytes.FieldsFunc with
strings.FieldFunc.

Fixes #38630

Change-Id: Iabbf9ca3dff0daa41f4ec930a21a3dd98e19f122
Reviewed-on: https://go-review.googlesource.com/c/go/+/230797
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Martin Möhrmann 2020-04-29 12:23:32 +02:00
parent 35dce1d67c
commit f2163c4d45
2 changed files with 6 additions and 2 deletions
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5
src/bytes/bytes.go
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@ -445,8 +445,9 @@ func Fields(s []byte) [][]byte {
// It splits the slice s at each run of code points c satisfying f(c) and // It splits the slice s at each run of code points c satisfying f(c) and
// returns a slice of subslices of s. If all code points in s satisfy f(c), or // returns a slice of subslices of s. If all code points in s satisfy f(c), or
// len(s) == 0, an empty slice is returned. // len(s) == 0, an empty slice is returned.
// FieldsFunc makes no guarantees about the order in which it calls f(c). //
// If f does not return consistent results for a given c, FieldsFunc may crash. // FieldsFunc makes no guarantees about the order in which it calls f(c)
// and assumes that f always returns the same value for a given c.
func FieldsFunc(s []byte, f func(rune) bool) [][]byte { func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
// A span is used to record a slice of s of the form s[start:end]. // A span is used to record a slice of s of the form s[start:end].
// The start index is inclusive and the end index is exclusive. // The start index is inclusive and the end index is exclusive.

3
src/strings/strings.go
View File

@ -369,6 +369,9 @@ func Fields(s string) []string {
// FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c) // FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c)
// and returns an array of slices of s. If all code points in s satisfy f(c) or the // and returns an array of slices of s. If all code points in s satisfy f(c) or the
// string is empty, an empty slice is returned. // string is empty, an empty slice is returned.
//
// FieldsFunc makes no guarantees about the order in which it calls f(c)
// and assumes that f always returns the same value for a given c.
func FieldsFunc(s string, f func(rune) bool) []string { func FieldsFunc(s string, f func(rune) bool) []string {
// A span is used to record a slice of s of the form s[start:end]. // A span is used to record a slice of s of the form s[start:end].
// The start index is inclusive and the end index is exclusive. // The start index is inclusive and the end index is exclusive.