Go 函数式编程

by · 2018年04月03日 · 726 Words · ~2min reading time | Improve on


原文链接： Go 函数式编程

可变参数函数

// 定义多类型参数
func Fullname(id int, names ...stirng) []string {
  println(strings.Join(names, " "))
  return names //返回参数
}
// 1. 普通调用
Fullname(1,"carl", "sagan")
// 2.传入多切片动态传入
names := []string{"carl", "sagan"}
Fullname(1,append([]string{"mr."}, names...)...) //先将这个切片展开，并通过 append 函数追加到 []string{"mr.")，然后将扩展后的切片展开供 toFullname 可变参数函数使用

匿名函数

匿名函数可赋值给变量,做为结构字段,或者在 channel 里里传送。

Each

Each func(func(A int), []A)
Each func(func(A B), []A)

Applies the given iterator function to each element of a collection (slice or map).

If the collection is a Slice, the iterator function arguments are value, index

If the collection is a Map, the iterator function arguments are value, key

EachP is a Parallel implementation of Each and concurrently applies the given iterator function to each element of a collection (slice or map).

  // var Each func(func(value interface{}, i interface{}), interface{})

  var buffer bytes.Buffer

  fn := func(s, i interface{}) {
    buffer.WriteString(s.(string))
  }

  s := []string{"a", "b", "c", "d", "e"}
  Each(fn, s)

  expect := "abcde"

  e := un.Each(fn, s)

  fmt.Printf("%#v\n", e) //"abcde"

Typed Each can be defined using a function type and the MakeEach helper.

Using a Typed Slice

  var EachInt func(func(value, i int), []int)
  MakeEach(&EachInt)

  var sum int

  fn := func(v, i int) {
    sum += v
  }

  i := []int{1, 2, 3, 4, 5}
  EachInt(fn, i)

  fmt.Printf("%#v\n", sum) //15

Using a Typed Map

  var EachStringInt func(func(key string, value int), map[string]int)
  var sum int

  fn := func(v int, k string) {
    sum += v
  }

  m := map[string]int{"a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
  EachStringInt(fn, m)

  fmt.Printf("%#v\n", sum) //15

Of note is the ability to close over variables within the calling scope.

Every

Map

Map func([]A, func(A) B) []B

Applies the given function to each element of a slice, returning a slice of results

The base Map function accepts interface{} types and returns []interface{}

  // Map func(interface{}, func(interface{}) interface{}) []interface{}

  s := []string{"a", "b", "c", "d"}

  fn := func(s interface{}) interface{} {
    return s.(string) + "!"
  }

  m := un.Map(ToI(s), fn)
  fmt.Println(m) //["a!", "b!", "c!", "d!"]

Typed Maps can be defined using a function type and the MakeMap helper.

  Map func([]A, func(A) B) []B

  var SMap func([]string, func(string) string) []string
  un.MakeMap(&SMap)

  m := un.SMap(s, fn)
  fmt.Println(m) //["a!", "b!", "c!", "d!"]

Of note is the return value of Map is a slice of the return type of the applied function.

Partition

Partition func([]A, func(A) bool) ([]A []A)

Partition splits a slice or map based on the evaluation of the supplied function

The base Partition function accepts interface{} types and returns []interface{}

  // Partition func(interface{}, func(interface{}) bool) ([]interface{}, []interface{})

  s := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

  fn := func(i interface{}) bool {
    return (i.(int) % 2) == 1
  }

  odd, even := un.Partition(s, fn)

  fmt.Println(odd)  //[1, 3, 5, 7, 9]
  fmt.Println(even) //[2, 4, 6, 8, 10]

Typed Partitions can be defined using a function type and the MakePartition helper.

  // Partition func([]A, func(A) bool) ([]A []A)

  var IPartition func([]int, func(int) bool) ([]int, []int)

  un.MakePartition(&IPartition)

  s := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

  fn := func(i int) bool {
    return (i % 2) == 1
  }

  odd, even := un.IPartition(s, fn)

  fmt.Println(odd)  //[1, 3, 5, 7, 9]
  fmt.Println(even) //[2, 4, 6, 8, 10]

Contains returns true if an object is in a slice.

  o := "a"
  s := []string{"a", "b", "c"}

  b := un.Contains(s, o)
  fmt.Println(b) //true

ToI converts a slice of arbitrary type []T into a slice of []interfaces{}

  s := []int{1, 1, 3, 5, 8, 13}
  i := un.ToI(s)

Notes

I am aware that the whole idea is not particularly very TheGoWay™, but it is useful as a learning exercise, and it is useful for moving fast and optimising later.

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