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lambda

Lambda Calculus

Anonymous Function: 이름을 갖을 필요가 없다.
Currying: 두 개 이상의 입력이 있는 함수는 최종적으로 1개의 입력만 받는 Lambda Calculus로 단순화 될 수 있다.

Lambda Function

Anonymous Function
First-class Function

Labda Function & Lambda Expression

IIFE

Immediately Invoked Function Expression

func(twoSeconds time.Duration) {
    // use twoSeconds
}(time.Second * 2)

Closure

Free&Bound Variable
Opend&Closed Expression

익명 함수가 함수 내 정의 되지 않은 변수를 참조하는 경우. 지역 함수가 전역 변수를 참조하는것과 유사함.

Usage

Isolating Data

package main

import "fmt"

func main() {
  gen := makeFibGen()
  for i := 0; i < 10; i++ {
    fmt.Println(gen())
  }
}

func makeFibGen() func() int {
  f1 := 0
  f2 := 1
  return func() int {
    f2, f1 = (f1 + f2), f2
    return f1
  }
}

Wrapping Functions and Creating Middleware

package main

import (
  "fmt"
  "net/http"
  "time"
)

func main() {
  http.HandleFunc("/hello", timed(hello))
  http.ListenAndServe(":3000", nil)
}

func timed(f func(http.ResponseWriter, *http.Request)) func(http.ResponseWriter, *http.Request) {
  return func(w http.ResponseWriter, r *http.Request) {
    start := time.Now()
    f(w, r)
    end := time.Now()
    fmt.Println("The request took", end.Sub(start))
  }
}

func hello(w http.ResponseWriter, r *http.Request) {
  fmt.Fprintln(w, "<h1>Hello!</h1>")
}

Accessing data that typically isn’t available

package main

import (
  "fmt"
  "net/http"
)

type Database struct {
  Url string
}

func NewDatabase(url string) Database {
  return Database{url}
}

func main() {
  db := NewDatabase("localhost:5432")

  http.HandleFunc("/hello", hello(db))
  http.ListenAndServe(":3000", nil)
}

func hello(db Database) func(http.ResponseWriter, *http.Request) {
  return func(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, db.Url)
  }
}

Binary Searching with the sort package

package main

import (
  "fmt"
  "sort"
)

func main() {
  numbers := []int{1, 11, -5, 8, 2, 0, 12}
  sort.Ints(numbers)
  fmt.Println("Sorted:", numbers)

  index := sort.Search(len(numbers), func(i int) bool {
    return numbers[i] >= 7
  })
  fmt.Println("The first number >= 7 is at index:", index)
  fmt.Println("The first number >= 7 is:", numbers[index])
}

Deferring Work

go func() {
  result := doWork1(a, b)
  result = doWork2(result)
  result = doWork3(result)
  // Use the final result
}()
fmt.Println("hi!")