mfr

README

mfr

(Immutable) Map/Filter/Reduce functions (+ friends).

Disclaimer: if you need as much performance as possible, this library is not for you.

Install

$ go get github.com/bnert/mfr

Note: must have go1.18 installed.

Example Usage (Map/Filter/Reduce)

package main

import (
  "fmt"
  "github.com/bnert/mfr"
)

type Data struct {
  Value int `json:"value"`
}

func main() {
  d1 := []Data{
    Data{Value: 0},
    Data{Value: 1},
    Data{Value: 2},
    Data{Value: 3},
    Data{Value: 4},
  }

  // Map to a different type
  d2 := mfr.Map[Data, int](d1, func(ctx mfr.Ctx[Data]) int) []int {
    return ctx.Item.Value * 3
  })

  d3 := mfr.Filter[Data](d2, func(ctx mfr.Ctx[Data]) bool) []Data {
    return ctx.Item % 2 == 0
  })

  sum := mfr.Reduce[int, int](d3, 0, func(ctx mfr.Ctx[int], acc int) int {
    return ctx.Current + ctx.Item
  })

  // Prints:
  // Reduced even sum: 18
  fmt.Println("Reduced evens sum:", sum)
}

Please see examples/ and tests/ directory for other examples of how this library can be used to write (somewhat) functional go.

Documentation

Index

• func EntriesToMap[K comparable, V any](entries []Entry[K, V]) map[K]V
• func Filter[T any](s []T, fn func(Ctx[T]) bool) []T
• func ForEach[T any](s []T, fn func(Ctx[T]))
• func Map[From any, To any](s []From, fn func(Ctx[From]) To) []To
• func Reduce[From any, To any](s []From, init To, fn func(Ctx[From], To) To) To
• type Ctx
• type Entry
  • func EntriesFromMap[K comparable, V any](m map[K]V) []Entry[K, V]

Functions

func EntriesToMap

func EntriesToMap[K comparable, V any](entries []Entry[K, V]) map[K]V

EntriesToMap converts an array of entries back into a map

func Filter

func Filter[T any](s []T, fn func(Ctx[T]) bool) []T

Filter returns an array of items for which the provided function returns true.

func ForEach

func ForEach[T any](s []T, fn func(Ctx[T]))

ForEach iterates over each item of the provided array, calling the provided function for each item.

func Map

func Map[From any, To any](s []From, fn func(Ctx[From]) To) []To

Map maps one type to another, via the transform function provided.

func Reduce

func Reduce[From any, To any](s []From, init To, fn func(Ctx[From], To) To) To

Reduce reduces and/or collects from an array to a target type, from an initial value.

Types

type Ctx

type Ctx[T any] struct {
	// Array is the
	Array   []T
	Index   int
	IsFirst bool
	IsLast  bool
	Item    T
}

Ctx is the context passed to Map/Filter/Reduce/ForEach

type Entry

type Entry[K any, V any] struct {
	Key   K
	Value V
}

Entry is a struct representation of an entry in a map.

func EntriesFromMap

func EntriesFromMap[K comparable, V any](m map[K]V) []Entry[K, V]

EntriesFromMap returns an array of entries, enabling maps to be used with Map/Reduce/Filter/ForEach