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slices.go
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slices.go
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// Copyright 2021 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 slices defines various functions useful with slices of any type.
// Unless otherwise specified, these functions all apply to the elements
// of a slice at index 0 <= i < len(s).
package genh
// 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[S ~[]E, E comparable](s1, s2 S) bool {
if len(s1) != len(s2) {
return false
}
for i := range s1 {
if s1[i] != s2[i] {
return false
}
}
return true
}
// 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[S1 ~[]E1, S2 ~[]E2, E1, E2 any](s1 S1, s2 S2, eq func(E1, E2) bool) bool {
if len(s1) != len(s2) {
return false
}
for i, v1 := range s1 {
v2 := s2[i]
if !eq(v1, v2) {
return false
}
}
return true
}
// 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[S ~[]E, E Ordered](s1, s2 S) int {
s2len := len(s2)
for i, v1 := range s1 {
if i >= s2len {
return +1
}
v2 := s2[i]
switch {
case v1 < v2:
return -1
case v1 > v2:
return +1
}
}
if len(s1) < s2len {
return -1
}
return 0
}
// 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[S1 ~[]E1, S2 ~[]E2, E1, E2 any](s1 S1, s2 S2, cmp func(E1, E2) int) int {
s2len := len(s2)
for i, v1 := range s1 {
if i >= s2len {
return +1
}
v2 := s2[i]
if c := cmp(v1, v2); c != 0 {
return c
}
}
if len(s1) < s2len {
return -1
}
return 0
}
// Index returns the index of the first occurrence of v in s,
// or -1 if not present.
func Index[S ~[]E, E comparable](s S, v E) int {
for i, vs := range s {
if v == vs {
return i
}
}
return -1
}
// IndexFunc returns the first index i satisfying f(s[i]),
// or -1 if none do.
func IndexFunc[S ~[]E, E any](s S, f func(E) bool) int {
for i, v := range s {
if f(v) {
return i
}
}
return -1
}
// Contains reports whether v is present in s.
func Contains[S ~[]E, E comparable](s S, v E) bool {
return Index(s, v) > -1
}
// ContainsFunc reports whether f(v) is present in s.
func ContainsFunc[S ~[]E, E any](s S, f func(E) bool) bool {
return IndexFunc(s, f) > -1
}
// 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 {
tot := len(s) + len(v)
if tot <= cap(s) {
s2 := s[:tot]
copy(s2[i+len(v):], s[i:])
copy(s2[i:], v)
return s2
}
s2 := make(S, tot)
copy(s2, s[:i])
copy(s2[i:], v)
copy(s2[i+len(v):], s[i:])
return s2
}
// 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-i)), 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.
func Delete[S ~[]E, E any](s S, i, j int) S {
return append(s[:i], s[j:]...)
}
// SliceClone returns a copy of the slice.
// The elements are copied using assignment, so this is a shallow clone.
func SliceClone[S ~[]E, E any](s S) S {
// Preserve nil in case it matters.
if s == nil {
return nil
}
return append(S([]E{}), 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.
func Compact[S ~[]E, E comparable](s S) S {
if len(s) == 0 {
return s
}
i := 1
last := s[0]
for _, v := range s[1:] {
if v != last {
s[i] = v
i++
last = v
}
}
return s[:i]
}
// CompactFunc is like Compact but uses a comparison function.
func CompactFunc[S ~[]E, E any](s S, eq func(E, E) bool) S {
if len(s) == 0 {
return s
}
i := 1
last := s[0]
for _, v := range s[1:] {
if !eq(v, last) {
s[i] = v
i++
last = v
}
}
return s[:i]
}
// 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. Grow may modify elements of the
// slice between the length and the capacity. If n is negative or too large to
// allocate the memory, Grow panics.
func Grow[S ~[]E, E any](s S, n int) S {
return append(s, make(S, n)...)[:len(s)]
}
// Clip removes unused capacity from the slice, returning s[:len(s):len(s)].
func Clip[S ~[]E, E any](s S) S {
return s[:len(s):len(s)]
}