1// run -gcflags=-G=3 2 3// Copyright 2021 The Go Authors. All rights reserved. 4// Use of this source code is governed by a BSD-style 5// license that can be found in the LICENSE file. 6 7// Package slices provides functions for basic operations on 8// slices of any element type. 9package main 10 11import ( 12 "fmt" 13 "math" 14 "strings" 15) 16 17type Ordered interface { 18 ~int | ~int8 | ~int16 | ~int32 | ~int64 | 19 ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr | 20 ~float32 | ~float64 | 21 ~string 22} 23 24type Integer interface { 25 ~int | ~int8 | ~int16 | ~int32 | ~int64 | 26 ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr 27} 28 29// Max returns the maximum of two values of some ordered type. 30func _Max[T Ordered](a, b T) T { 31 if a > b { 32 return a 33 } 34 return b 35} 36 37// Min returns the minimum of two values of some ordered type. 38func _Min[T Ordered](a, b T) T { 39 if a < b { 40 return a 41 } 42 return b 43} 44 45// _Equal reports whether two slices are equal: the same length and all 46// elements equal. All floating point NaNs are considered equal. 47func _Equal[Elem comparable](s1, s2 []Elem) bool { 48 if len(s1) != len(s2) { 49 return false 50 } 51 for i, v1 := range s1 { 52 v2 := s2[i] 53 if v1 != v2 { 54 isNaN := func(f Elem) bool { return f != f } 55 if !isNaN(v1) || !isNaN(v2) { 56 return false 57 } 58 } 59 } 60 return true 61} 62 63// _EqualFn reports whether two slices are equal using a comparison 64// function on each element. 65func _EqualFn[Elem any](s1, s2 []Elem, eq func(Elem, Elem) bool) bool { 66 if len(s1) != len(s2) { 67 return false 68 } 69 for i, v1 := range s1 { 70 v2 := s2[i] 71 if !eq(v1, v2) { 72 return false 73 } 74 } 75 return true 76} 77 78// _Map turns a []Elem1 to a []Elem2 using a mapping function. 79func _Map[Elem1, Elem2 any](s []Elem1, f func(Elem1) Elem2) []Elem2 { 80 r := make([]Elem2, len(s)) 81 for i, v := range s { 82 r[i] = f(v) 83 } 84 return r 85} 86 87// _Reduce reduces a []Elem1 to a single value of type Elem2 using 88// a reduction function. 89func _Reduce[Elem1, Elem2 any](s []Elem1, initializer Elem2, f func(Elem2, Elem1) Elem2) Elem2 { 90 r := initializer 91 for _, v := range s { 92 r = f(r, v) 93 } 94 return r 95} 96 97// _Filter filters values from a slice using a filter function. 98func _Filter[Elem any](s []Elem, f func(Elem) bool) []Elem { 99 var r []Elem 100 for _, v := range s { 101 if f(v) { 102 r = append(r, v) 103 } 104 } 105 return r 106} 107 108// _Max returns the maximum element in a slice of some ordered type. 109// If the slice is empty it returns the zero value of the element type. 110func _SliceMax[Elem Ordered](s []Elem) Elem { 111 if len(s) == 0 { 112 var zero Elem 113 return zero 114 } 115 return _Reduce(s[1:], s[0], _Max[Elem]) 116} 117 118// _Min returns the minimum element in a slice of some ordered type. 119// If the slice is empty it returns the zero value of the element type. 120func _SliceMin[Elem Ordered](s []Elem) Elem { 121 if len(s) == 0 { 122 var zero Elem 123 return zero 124 } 125 return _Reduce(s[1:], s[0], _Min[Elem]) 126} 127 128// _Append adds values to the end of a slice, returning a new slice. 129// This is like the predeclared append function; it's an example 130// of how to write it using generics. We used to write code like 131// this before append was added to the language, but we had to write 132// a separate copy for each type. 133func _Append[T any](s []T, t ...T) []T { 134 lens := len(s) 135 tot := lens + len(t) 136 if tot <= cap(s) { 137 s = s[:tot] 138 } else { 139 news := make([]T, tot, tot+tot/2) 140 _Copy(news, s) 141 s = news 142 } 143 _Copy(s[lens:tot], t) 144 return s 145} 146 147// _Copy copies values from t to s, stopping when either slice is full, 148// returning the number of values copied. This is like the predeclared 149// copy function; it's an example of how to write it using generics. 150func _Copy[T any](s, t []T) int { 151 i := 0 152 for ; i < len(s) && i < len(t); i++ { 153 s[i] = t[i] 154 } 155 return i 156} 157 158func TestEqual() { 159 s1 := []int{1, 2, 3} 160 if !_Equal(s1, s1) { 161 panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s1, s1)) 162 } 163 s2 := []int{1, 2, 3} 164 if !_Equal(s1, s2) { 165 panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s1, s2)) 166 } 167 s2 = append(s2, 4) 168 if _Equal(s1, s2) { 169 panic(fmt.Sprintf("_Equal(%v, %v) = true, want false", s1, s2)) 170 } 171 172 s3 := []float64{1, 2, math.NaN()} 173 if !_Equal(s3, s3) { 174 panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s3, s3)) 175 } 176 177 if _Equal(s1, nil) { 178 panic(fmt.Sprintf("_Equal(%v, nil) = true, want false", s1)) 179 } 180 if _Equal(nil, s1) { 181 panic(fmt.Sprintf("_Equal(nil, %v) = true, want false", s1)) 182 } 183 if !_Equal(s1[:0], nil) { 184 panic(fmt.Sprintf("_Equal(%v, nil = false, want true", s1[:0])) 185 } 186} 187 188func offByOne[Elem Integer](a, b Elem) bool { 189 return a == b+1 || a == b-1 190} 191 192func TestEqualFn() { 193 s1 := []int{1, 2, 3} 194 s2 := []int{2, 3, 4} 195 if _EqualFn(s1, s1, offByOne[int]) { 196 panic(fmt.Sprintf("_EqualFn(%v, %v, offByOne) = true, want false", s1, s1)) 197 } 198 if !_EqualFn(s1, s2, offByOne[int]) { 199 panic(fmt.Sprintf("_EqualFn(%v, %v, offByOne) = false, want true", s1, s2)) 200 } 201 202 if !_EqualFn(s1[:0], nil, offByOne[int]) { 203 panic(fmt.Sprintf("_EqualFn(%v, nil, offByOne) = false, want true", s1[:0])) 204 } 205 206 s3 := []string{"a", "b", "c"} 207 s4 := []string{"A", "B", "C"} 208 if !_EqualFn(s3, s4, strings.EqualFold) { 209 panic(fmt.Sprintf("_EqualFn(%v, %v, strings.EqualFold) = false, want true", s3, s4)) 210 } 211} 212 213func TestMap() { 214 s1 := []int{1, 2, 3} 215 s2 := _Map(s1, func(i int) float64 { return float64(i) * 2.5 }) 216 if want := []float64{2.5, 5, 7.5}; !_Equal(s2, want) { 217 panic(fmt.Sprintf("_Map(%v, ...) = %v, want %v", s1, s2, want)) 218 } 219 220 s3 := []string{"Hello", "World"} 221 s4 := _Map(s3, strings.ToLower) 222 if want := []string{"hello", "world"}; !_Equal(s4, want) { 223 panic(fmt.Sprintf("_Map(%v, strings.ToLower) = %v, want %v", s3, s4, want)) 224 } 225 226 s5 := _Map(nil, func(i int) int { return i }) 227 if len(s5) != 0 { 228 panic(fmt.Sprintf("_Map(nil, identity) = %v, want empty slice", s5)) 229 } 230} 231 232func TestReduce() { 233 s1 := []int{1, 2, 3} 234 r := _Reduce(s1, 0, func(f float64, i int) float64 { return float64(i)*2.5 + f }) 235 if want := 15.0; r != want { 236 panic(fmt.Sprintf("_Reduce(%v, 0, ...) = %v, want %v", s1, r, want)) 237 } 238 239 if got := _Reduce(nil, 0, func(i, j int) int { return i + j }); got != 0 { 240 panic(fmt.Sprintf("_Reduce(nil, 0, add) = %v, want 0", got)) 241 } 242} 243 244func TestFilter() { 245 s1 := []int{1, 2, 3} 246 s2 := _Filter(s1, func(i int) bool { return i%2 == 0 }) 247 if want := []int{2}; !_Equal(s2, want) { 248 panic(fmt.Sprintf("_Filter(%v, even) = %v, want %v", s1, s2, want)) 249 } 250 251 if s3 := _Filter(s1[:0], func(i int) bool { return true }); len(s3) > 0 { 252 panic(fmt.Sprintf("_Filter(%v, identity) = %v, want empty slice", s1[:0], s3)) 253 } 254} 255 256func TestMax() { 257 s1 := []int{1, 2, 3, -5} 258 if got, want := _SliceMax(s1), 3; got != want { 259 panic(fmt.Sprintf("_Max(%v) = %d, want %d", s1, got, want)) 260 } 261 262 s2 := []string{"aaa", "a", "aa", "aaaa"} 263 if got, want := _SliceMax(s2), "aaaa"; got != want { 264 panic(fmt.Sprintf("_Max(%v) = %q, want %q", s2, got, want)) 265 } 266 267 if got, want := _SliceMax(s2[:0]), ""; got != want { 268 panic(fmt.Sprintf("_Max(%v) = %q, want %q", s2[:0], got, want)) 269 } 270} 271 272func TestMin() { 273 s1 := []int{1, 2, 3, -5} 274 if got, want := _SliceMin(s1), -5; got != want { 275 panic(fmt.Sprintf("_Min(%v) = %d, want %d", s1, got, want)) 276 } 277 278 s2 := []string{"aaa", "a", "aa", "aaaa"} 279 if got, want := _SliceMin(s2), "a"; got != want { 280 panic(fmt.Sprintf("_Min(%v) = %q, want %q", s2, got, want)) 281 } 282 283 if got, want := _SliceMin(s2[:0]), ""; got != want { 284 panic(fmt.Sprintf("_Min(%v) = %q, want %q", s2[:0], got, want)) 285 } 286} 287 288func TestAppend() { 289 s := []int{1, 2, 3} 290 s = _Append(s, 4, 5, 6) 291 want := []int{1, 2, 3, 4, 5, 6} 292 if !_Equal(s, want) { 293 panic(fmt.Sprintf("after _Append got %v, want %v", s, want)) 294 } 295} 296 297func TestCopy() { 298 s1 := []int{1, 2, 3} 299 s2 := []int{4, 5} 300 if got := _Copy(s1, s2); got != 2 { 301 panic(fmt.Sprintf("_Copy returned %d, want 2", got)) 302 } 303 want := []int{4, 5, 3} 304 if !_Equal(s1, want) { 305 panic(fmt.Sprintf("after _Copy got %v, want %v", s1, want)) 306 } 307} 308func main() { 309 TestEqual() 310 TestEqualFn() 311 TestMap() 312 TestReduce() 313 TestFilter() 314 TestMax() 315 TestMin() 316 TestAppend() 317 TestCopy() 318} 319