From f285d1f8e00405771e647fc3fa615d132340b28f Mon Sep 17 00:00:00 2001
From: Leon Mika <lmika@lmika.com>
Date: Thu, 19 Jun 2025 13:20:29 +0200
Subject: [PATCH] Add MaxIndex function

---
 moslice/map.go      | 13 +++++++++++++
 moslice/map_test.go | 20 +++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/moslice/map.go b/moslice/map.go
index 78a9451..73fd2eb 100644
--- a/moslice/map.go
+++ b/moslice/map.go
@@ -13,6 +13,19 @@ func Map[T, U any](ts []T, fn func(t T) U) (us []U) {
 	return us
 }
 
+// Map returns a new slice containing the elements of ts transformed by the passed in function.
+func MapIndex[T, U any](ts []T, fn func(t T, index int) U) (us []U) {
+	if ts == nil {
+		return nil
+	}
+
+	us = make([]U, len(ts))
+	for i, t := range ts {
+		us[i] = fn(t, i)
+	}
+	return us
+}
+
 // Map returns a new slice containing the elements of ts transformed by the passed in function, which
 // can either either a mapped value of U, or an error. If the mapping function returns an error, MapWithError
 // will return nil and the returned error.
diff --git a/moslice/map_test.go b/moslice/map_test.go
index d15bf7d..4270c19 100644
--- a/moslice/map_test.go
+++ b/moslice/map_test.go
@@ -2,9 +2,10 @@ package moslice_test
 
 import (
 	"errors"
-	"lmika.dev/pkg/modash/moslice"
 	"testing"
 
+	"lmika.dev/pkg/modash/moslice"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -24,6 +25,23 @@ func TestMap(t *testing.T) {
 	})
 }
 
+func TestMapIndex(t *testing.T) {
+	t.Run("should return a map and index slice", func(t *testing.T) {
+		ts := []int{1, 2, 3}
+		us := moslice.MapIndex(ts, func(_ int, i int) int { return i })
+
+		assert.Equal(t, []int{0, 1, 2}, us)
+	})
+
+	t.Run("should return nil if passed in nil", func(t *testing.T) {
+		ts := []int(nil)
+		us := moslice.MapIndex(ts, func(_, i int) int { return i })
+
+		assert.Nil(t, us)
+	})
+}
+
+
 func TestMapWithError(t *testing.T) {
 	t.Run("should return a mapped slice with no error", func(t *testing.T) {
 		ts := []int{1, 2, 3}