Retain & Filter refactor (#46)

`sliceext.Retain` & `sliceext.Filter` to not shuffle data in the
underlying slice array but create new slice referencing the data
instead. In practice, it can cause unexpected behaviour and users
expectations not met when the same data is also referenced elsewhere. If
anyone still requires a `shuffle` implementation for efficiency I'd be
happy to add a separate function for that as well.

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [5.27.0] - 2024-01-29
+### Changed
+- `sliceext.Retain` & `sliceext.Filter` to not shuffle data in the underlying slice array but create new slice referencing the data instead. In practice, it can cause unexpected behaviour and users expectations not met when the same data is also referenced elsewhere. If anyone still requires a `shuffle` implementation for efficiency I'd be happy to add a separate function for that as well.
+
 ## [5.26.0] - 2024-01-28
 ### Added
 - `stringsext.Join` a more ergonomic way to join strings with a separator when you don't have a slice of strings.

README.md

@@ -1,6 +1,6 @@
 # pkg
 
-![Project status](https://img.shields.io/badge/version-5.26.0-green.svg)
+![Project status](https://img.shields.io/badge/version-5.27.0-green.svg)
 [![Lint & Test](https://github.com/go-playground/pkg/actions/workflows/go.yml/badge.svg)](https://github.com/go-playground/pkg/actions/workflows/go.yml)
 [![Coverage Status](https://coveralls.io/repos/github/go-playground/pkg/badge.svg?branch=master)](https://coveralls.io/github/go-playground/pkg?branch=master)
 [![GoDoc](https://godoc.org/github.com/go-playground/pkg?status.svg)](https://pkg.go.dev/mod/github.com/go-playground/pkg/v5)

slice/slice.go

@@ -4,37 +4,38 @@
 package sliceext
 
 import (
-	optionext "github.com/go-playground/pkg/v5/values/option"
 	"sort"
+
+	optionext "github.com/go-playground/pkg/v5/values/option"
 )
 
 // Retain retains only the elements specified by the function.
 //
-// This shuffles and returns the retained values of the slice.
+// This returns a new slice with references to the underlying data instead of shuffling.
 func Retain[T any](slice []T, fn func(v T) bool) []T {
-	var j int
+	results := make([]T, 0, len(slice))
 	for _, v := range slice {
+		v := v
 		if fn(v) {
-			slice[j] = v
-			j++
+			results = append(results, v)
 		}
 	}
-	return slice[:j]
+	return results
 }
 
 // Filter filters out the elements specified by the function.
 //
-// This shuffles and returns the retained values of the slice.
+// This returns a new slice with references to the underlying data instead of shuffling.
 func Filter[T any](slice []T, fn func(v T) bool) []T {
-	var j int
+	results := make([]T, 0, len(slice))
 	for _, v := range slice {
+		v := v
 		if fn(v) {
 			continue
 		}
-		slice[j] = v
-		j++
+		results = append(results, v)
 	}
-	return slice[:j]
+	return results
 }
 
 // Map maps a slice of []T -> []U using the map function.