slices.go

     1  // Copyright 2019 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  
     5  // Package slices implements various slice algorithms.
     6  package slices
     7  
     8  // Map turns a []T1 to a []T2 using a mapping function.
     9  func Map[T1, T2 any](s []T1, f func(T1) T2) []T2 {
    10  	r := make([]T2, len(s))
    11  	for i, v := range s {
    12  		r[i] = f(v)
    13  	}
    14  	return r
    15  }
    16  
    17  // Reduce reduces a []T1 to a single value using a reduction function.
    18  func Reduce[T1, T2 any](s []T1, initializer T2, f func(T2, T1) T2) T2 {
    19  	r := initializer
    20  	for _, v := range s {
    21  		r = f(r, v)
    22  	}
    23  	return r
    24  }
    25  
    26  // Filter filters values from a slice using a filter function.
    27  func Filter[T any](s []T, f func(T) bool) []T {
    28  	var r []T
    29  	for _, v := range s {
    30  		if f(v) {
    31  			r = append(r, v)
    32  		}
    33  	}
    34  	return r
    35  }
    36  
    37  // Example uses
    38  
    39  func limiter(x int) byte {
    40  	switch {
    41  	case x < 0:
    42  		return 0
    43  	default:
    44  		return byte(x)
    45  	case x > 255:
    46  		return 255
    47  	}
    48  }
    49  
    50  var input = []int{-4, 68954, 7, 44, 0, -555, 6945}
    51  var limited1 = Map[int, byte](input, limiter)
    52  var limited2 = Map(input, limiter) // using type inference
    53  
    54  func reducer(x float64, y int) float64 {
    55  	return x + float64(y)
    56  }
    57  
    58  var reduced1 = Reduce[int, float64](input, 0, reducer)
    59  var reduced2 = Reduce(input, 1i /* ERROR "overflows" */, reducer) // using type inference
    60  var reduced3 = Reduce(input, 1, reducer) // using type inference
    61  
    62  func filter(x int) bool {
    63  	return x&1 != 0
    64  }
    65  
    66  var filtered1 = Filter[int](input, filter)
    67  var filtered2 = Filter(input, filter) // using type inference
    68  
    69
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