1// Copyright 2021 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package a 6 7type Ordered interface { 8 ~int | ~int8 | ~int16 | ~int32 | ~int64 | 9 ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr | 10 ~float32 | ~float64 | 11 ~string 12} 13 14// Max returns the maximum of two values of some ordered type. 15func Max[T Ordered](a, b T) T { 16 if a > b { 17 return a 18 } 19 return b 20} 21 22// Min returns the minimum of two values of some ordered type. 23func Min[T Ordered](a, b T) T { 24 if a < b { 25 return a 26 } 27 return b 28} 29 30// Equal reports whether two slices are equal: the same length and all 31// elements equal. All floating point NaNs are considered equal. 32func Equal[Elem comparable](s1, s2 []Elem) bool { 33 if len(s1) != len(s2) { 34 return false 35 } 36 for i, v1 := range s1 { 37 v2 := s2[i] 38 if v1 != v2 { 39 isNaN := func(f Elem) bool { return f != f } 40 if !isNaN(v1) || !isNaN(v2) { 41 return false 42 } 43 } 44 } 45 return true 46} 47 48// EqualFn reports whether two slices are equal using a comparison 49// function on each element. 50func EqualFn[Elem any](s1, s2 []Elem, eq func(Elem, Elem) bool) bool { 51 if len(s1) != len(s2) { 52 return false 53 } 54 for i, v1 := range s1 { 55 v2 := s2[i] 56 if !eq(v1, v2) { 57 return false 58 } 59 } 60 return true 61} 62 63// Map turns a []Elem1 to a []Elem2 using a mapping function. 64func Map[Elem1, Elem2 any](s []Elem1, f func(Elem1) Elem2) []Elem2 { 65 r := make([]Elem2, len(s)) 66 for i, v := range s { 67 r[i] = f(v) 68 } 69 return r 70} 71 72// Reduce reduces a []Elem1 to a single value of type Elem2 using 73// a reduction function. 74func Reduce[Elem1, Elem2 any](s []Elem1, initializer Elem2, f func(Elem2, Elem1) Elem2) Elem2 { 75 r := initializer 76 for _, v := range s { 77 r = f(r, v) 78 } 79 return r 80} 81 82// Filter filters values from a slice using a filter function. 83func Filter[Elem any](s []Elem, f func(Elem) bool) []Elem { 84 var r []Elem 85 for _, v := range s { 86 if f(v) { 87 r = append(r, v) 88 } 89 } 90 return r 91} 92 93// Max returns the maximum element in a slice of some ordered type. 94// If the slice is empty it returns the zero value of the element type. 95func SliceMax[Elem Ordered](s []Elem) Elem { 96 if len(s) == 0 { 97 var zero Elem 98 return zero 99 } 100 return Reduce(s[1:], s[0], Max[Elem]) 101} 102 103// Min returns the minimum element in a slice of some ordered type. 104// If the slice is empty it returns the zero value of the element type. 105func SliceMin[Elem Ordered](s []Elem) Elem { 106 if len(s) == 0 { 107 var zero Elem 108 return zero 109 } 110 return Reduce(s[1:], s[0], Min[Elem]) 111} 112 113// Append adds values to the end of a slice, returning a new slice. 114// This is like the predeclared append function; it's an example 115// of how to write it using generics. We used to write code like 116// this before append was added to the language, but we had to write 117// a separate copy for each type. 118func Append[T any](s []T, t ...T) []T { 119 lens := len(s) 120 tot := lens + len(t) 121 if tot <= cap(s) { 122 s = s[:tot] 123 } else { 124 news := make([]T, tot, tot+tot/2) 125 Copy(news, s) 126 s = news 127 } 128 Copy(s[lens:tot], t) 129 return s 130} 131 132// Copy copies values from t to s, stopping when either slice is full, 133// returning the number of values copied. This is like the predeclared 134// copy function; it's an example of how to write it using generics. 135func Copy[T any](s, t []T) int { 136 i := 0 137 for ; i < len(s) && i < len(t); i++ { 138 s[i] = t[i] 139 } 140 return i 141} 142