Closed
Description
In #45955 I proposed a new slices package in the standard library. After considerable discussion there and in discussion #47203 we settled on an API and added the experimental package golang.org/x/exp/slices.
We now have experience with this package in practice. pkg.go.dev reports that it is imported by 1,541 other packages. I propose that it is now time to move this package into the standard library for the 1.21 release.
Doing this doesn't mean that we can't add more functions to the standard library slices package later. Any such additions should be suggested in their own separate proposal.
The specific API that we will put into the standard library appears below.
This description of the API refers to constraints.Ordered in a few places; if the constraints package is not present in the standard library, that reference will be replaced by an unexported constraint with the same set of types.
Note that we should either accept or reject #57348 before we accept this proposal. If we accept #57348, the appropriate change will be made here.
I'm not aware of any other proposal to modify the existing slices package API. There are a few proposals to add new functions to the slices package (at least #52434, #53987, #54768, #56353); those proposals can move from x/exp/slices to just plain slices.
Proposed API:
// Equal reports whether two slices are equal: the same length and all
// elements equal. If the lengths are different, Equal returns false.
// Otherwise, the elements are compared in increasing index order, and the
// comparison stops at the first unequal pair.
// Floating point NaNs are not considered equal.
func Equal[E comparable](s1, s2 []E) bool
// EqualFunc reports whether two slices are equal using a comparison
// function on each pair of elements. If the lengths are different,
// EqualFunc returns false. Otherwise, the elements are compared in
// increasing index order, and the comparison stops at the first index
// for which eq returns false.
func EqualFunc[E1, E2 any](s1 []E1, s2 []E2, eq func(E1, E2) bool) bool
// Compare compares the elements of s1 and s2.
// The elements are compared sequentially, starting at index 0,
// until one element is not equal to the other.
// The result of comparing the first non-matching elements is returned.
// If both slices are equal until one of them ends, the shorter slice is
// considered less than the longer one.
// The result is 0 if s1 == s2, -1 if s1 < s2, and +1 if s1 > s2.
// Comparisons involving floating point NaNs are ignored.
func Compare[E constraints.Ordered](s1, s2 []E) int
// CompareFunc is like Compare but uses a comparison function
// on each pair of elements. The elements are compared in increasing
// index order, and the comparisons stop after the first time cmp
// returns non-zero.
// The result is the first non-zero result of cmp; if cmp always
// returns 0 the result is 0 if len(s1) == len(s2), -1 if len(s1) < len(s2),
// and +1 if len(s1) > len(s2).
func CompareFunc[E1, E2 any](s1 []E1, s2 []E2, cmp func(E1, E2) int) int
// Index returns the index of the first occurrence of v in s,
// or -1 if not present.
func Index[E comparable](s []E, v E) int
// IndexFunc returns the first index i satisfying f(s[i]),
// or -1 if none do.
func IndexFunc[E any](s []E, f func(E) bool) int
// Contains reports whether v is present in s.
func Contains[E comparable](s []E, v E) bool
// ContainsFunc reports whether at least one
// element e of s satisfies f(e).
func ContainsFunc[E any](s []E, f func(E) bool) bool
// Insert inserts the values v... into s at index i,
// returning the modified slice.
// In the returned slice r, r[i] == v[0].
// Insert panics if i is out of range.
// This function is O(len(s) + len(v)).
func Insert[S ~[]E, E any](s S, i int, v ...E) S
// Delete removes the elements s[i:j] from s, returning the modified slice.
// Delete panics if s[i:j] is not a valid slice of s.
// Delete modifies the contents of the slice s; it does not create a new slice.
// Delete is O(len(s)-j), so if many items must be deleted, it is better to
// make a single call deleting them all together than to delete one at a time.
// Delete might not modify the elements s[len(s)-(j-i):len(s)]. If those
// elements contain pointers you might consider zeroing those elements so that
// objects they reference can be garbage collected.
func Delete[S ~[]E, E any](s S, i, j int) S
// Replace replaces the elements s[i:j] by the given v, and returns the
// modified slice. Replace panics if s[i:j] is not a valid slice of s.
func Replace[S ~[]E, E any](s S, i, j int, v ...E) S
// Clone returns a copy of the slice.
// The elements are copied using assignment, so this is a shallow clone.
func Clone[S ~[]E, E any](s S) S
// Compact replaces consecutive runs of equal elements with a single copy.
// This is like the uniq command found on Unix.
// Compact modifies the contents of the slice s; it does not create a new slice.
// When Compact discards m elements in total, it might not modify the elements
// s[len(s)-m:len(s)]. If those elements contain pointers you might consider
// zeroing those elements so that objects they reference can be garbage collected.
func Compact[S ~[]E, E comparable](s S) S
// CompactFunc is like Compact but uses a comparison function.
func CompactFunc[S ~[]E, E any](s S, eq func(E, E) bool) S
// Grow increases the slice's capacity, if necessary, to guarantee space for
// another n elements. After Grow(n), at least n elements can be appended
// to the slice without another allocation. If n is negative or too large to
// allocate the memory, Grow panics.
func Grow[S ~[]E, E any](s S, n int) S
// Clip removes unused capacity from the slice, returning s[:len(s):len(s)].
func Clip[S ~[]E, E any](s S) S
// Sort sorts a slice of any ordered type in ascending order.
// Sort may fail to sort correctly when sorting slices of floating-point
// numbers containing Not-a-number (NaN) values.
// Use slices.SortFunc(x, func(a, b float64) bool {return a < b || (math.IsNaN(a) && !math.IsNaN(b))})
// instead if the input may contain NaNs.
func Sort[E constraints.Ordered](x []E)
// SortFunc sorts the slice x in ascending order as determined by the less function.
// This sort is not guaranteed to be stable.
//
// SortFunc requires that less is a strict weak ordering.
// See https://en.wikipedia.org/wiki/Weak_ordering#Strict_weak_orderings.
func SortFunc[E any](x []E, less func(a, b E) bool)
// SortStableFunc sorts the slice x while keeping the original order of equal
// elements, using less to compare elements.
func SortStableFunc[E any](x []E, less func(a, b E) bool)
// IsSorted reports whether x is sorted in ascending order.
func IsSorted[E constraints.Ordered](x []E) bool
// IsSortedFunc reports whether x is sorted in ascending order, with less as the
// comparison function.
func IsSortedFunc[E any](x []E, less func(a, b E) bool) bool
// BinarySearch searches for target in a sorted slice and returns the position
// where target is found, or the position where target would appear in the
// sort order; it also returns a bool saying whether the target is really found
// in the slice. The slice must be sorted in increasing order.
func BinarySearch[E constraints.Ordered](x []E, target E) (int, bool)
// BinarySearchFunc works like BinarySearch, but uses a custom comparison
// function. The slice must be sorted in increasing order, where "increasing" is
// defined by cmp. cmp(a, b) is expected to return an integer comparing the two
// parameters: 0 if a == b, a negative number if a < b and a positive number if
// a > b.
func BinarySearchFunc[E any](x []E, target E, cmp func(E, E) int) (int, bool)