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7455e027e9
We had this in a different repo, but moving it here, as this a more fitting package. Updates #cleanup Change-Id: I5fb9b10e465932aeef5841c67deba4d77d473d57 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
104 lines
2.7 KiB
Go
104 lines
2.7 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package slicesx contains some helpful generic slice functions.
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package slicesx
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import "math/rand"
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// Interleave combines two slices of the form [a, b, c] and [x, y, z] into a
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// slice with elements interleaved; i.e. [a, x, b, y, c, z].
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func Interleave[S ~[]T, T any](a, b S) S {
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// Avoid allocating an empty slice.
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if a == nil && b == nil {
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return nil
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}
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var (
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i int
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ret = make([]T, 0, len(a)+len(b))
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)
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for i = 0; i < len(a) && i < len(b); i++ {
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ret = append(ret, a[i], b[i])
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}
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ret = append(ret, a[i:]...)
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ret = append(ret, b[i:]...)
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return ret
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}
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// Shuffle randomly shuffles a slice in-place, similar to rand.Shuffle.
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func Shuffle[S ~[]T, T any](s S) {
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// TODO(andrew): use a pooled Rand?
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// This is the same Fisher-Yates shuffle implementation as rand.Shuffle
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n := len(s)
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i := n - 1
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for ; i > 1<<31-1-1; i-- {
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j := int(rand.Int63n(int64(i + 1)))
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s[i], s[j] = s[j], s[i]
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}
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for ; i > 0; i-- {
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j := int(rand.Int31n(int32(i + 1)))
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s[i], s[j] = s[j], s[i]
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}
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}
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// Partition returns two slices, the first containing the elements of the input
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// slice for which the callback evaluates to true, the second containing the rest.
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//
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// This function does not mutate s.
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func Partition[S ~[]T, T any](s S, cb func(T) bool) (trues, falses S) {
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for _, elem := range s {
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if cb(elem) {
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trues = append(trues, elem)
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} else {
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falses = append(falses, elem)
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}
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}
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return
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}
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// EqualSameNil reports whether two slices are equal: the same length, same
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// nilness (notably when length zero), and all elements equal. If the lengths
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// are different or their nilness differs, Equal returns false. Otherwise, the
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// elements are compared in increasing index order, and the comparison stops at
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// the first unequal pair. Floating point NaNs are not considered equal.
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//
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// It is identical to the standard library's slices.Equal but adds the matching
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// nilness check.
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func EqualSameNil[S ~[]E, E comparable](s1, s2 S) bool {
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if len(s1) != len(s2) || (s1 == nil) != (s2 == nil) {
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return false
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}
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for i := range s1 {
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if s1[i] != s2[i] {
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return false
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}
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}
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return true
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}
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// Filter calls fn with each element of the provided src slice, and appends the
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// element to dst if fn returns true.
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//
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// dst can be nil to allocate a new slice, or set to src[:0] to filter in-place
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// without allocating.
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func Filter[S ~[]T, T any](dst, src S, fn func(T) bool) S {
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for _, x := range src {
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if fn(x) {
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dst = append(dst, x)
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}
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}
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return dst
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}
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// AppendMatching appends elements in ps to dst if f(x) is true.
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func AppendMatching[T any](dst, ps []T, f func(T) bool) []T {
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for _, p := range ps {
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if f(p) {
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dst = append(dst, p)
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}
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}
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return dst
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}
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