funcy

README

funcy

Experiments with golang generics to implement functional favorites like filter, map, && reduce.

Installation

$ go get github.com/bfollek/funcy@latest

Documentation

https://pkg.go.dev/github.com/bfollek/funcy

Documentation

Overview

package funcy implements functional favorites like filter, map, and reduce.

You'll get a compile error if you try something that doesn't make sense. For example, using map to run strings.ToLower on a slice of ints:

sl := []int{1, 2, 3, 4}
result := Map(sl, strings.ToLower)

will get you an error like

pkg/funcy_test.go:64:20: type func(s string) string of strings.ToLower
does not match inferred type func(int) T2 for func(T1) T2

Index

• func Filter[T any](sl []T, test func(T) bool) []T
• func FilterWithIndex[T any](sl []T, test func(int, T) bool) []T
• func Map[T1, T2 any](sl []T1, transform func(T1) T2) []T2
• func MustTranspose[T any](sl [][]T) [][]T
• func Reduce[T1, T2 any](sl []T1, startValue T2, fReduce func(T2, T1) T2) T2
• func Sum[T constraints.Ordered](sl []T) T
• func Transpose[T any](sl [][]T) ([][]T, error)

Functions

func Filter

func Filter[T any](sl []T, test func(T) bool) []T

Filter takes a slice of any type and a predicate function. It passes each slice item to the predicate function, and returns a slice of the items for which the predicate function returns true.

func FilterWithIndex

func FilterWithIndex[T any](sl []T, test func(int, T) bool) []T

FilterWithIndex is like Filter, but the predicate function receives two arguments. The second argument is the slice item; the first argument is the item's index within the slice. FilterWithIndex returns a list of the items for which the predicate function returns true.

func Map

func Map[T1, T2 any](sl []T1, transform func(T1) T2) []T2

Map runs each item in a slice through a transformation function, and returns a slice of the transformed items. The transformed items may be a different type from the input items, e.g. strings to ints using strconv.Atoi.

Note: For functions that return multiple values, like strconv.Atoi, wrap the function in another function that returns a single value, and pass the wrapper as the transformation function. The wrapper can handle errors, etc.:

result := Map(input, func(s string) int {
	i, err := strconv.Atoi(s)
	if err != nil {
		log.Fatal(err)
	}
	return i
})

func MustTranspose

func MustTranspose[T any](sl [][]T) [][]T

MustTranspose calls Transpose and panics on error.

func Reduce

func Reduce[T1, T2 any](sl []T1, startValue T2, fReduce func(T2, T1) T2) T2

Reduce reduces a slice to a single value by running each item of the slice through a function that takes an accumulator and the next item as its paramaters. The classic example is reducing a slice of numbers by adding them together.

func Sum

func Sum[T constraints.Ordered](sl []T) T

Sum sums the items in a slice.

func Transpose

func Transpose[T any](sl [][]T) ([][]T, error)

Transpose converts a matrix from T[rows][columns] to T[columns][rows]. The matrix cannot be jagged, i.e. all rows must have the same number of elements.