adding index arguments to Map, ForEach and Reduce

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 1.1.0 (2022-03-03)
+
+Adding `i int` param to lo.Map(), lo.Filter(), lo.ForEach() and lo.Reduce() predicates.
+
 ## 1.0.0 (2022-03-02)
 
 *Initial release*

Makefile

@@ -28,7 +28,7 @@ tools:
 	${BIN} install github.com/psampaz/go-mod-outdated@latest
 	${BIN} install github.com/jondot/goweight@latest
 	${BIN} install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
-	${BIN} install golang.org/x/tools/cmd/cover
+	${BIN} get -t -u golang.org/x/tools/cmd/cover
 	${BIN} get -t -u github.com/sonatype-nexus-community/nancy@latest
 	go mod tidy
 

README.md

@@ -101,7 +101,7 @@ Constraints:
 Manipulates a slice and transforms it to a slice of another type:
 
 ```go
-lo.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64) string {
+lo.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
     return strconv.FormatInt(x, 10)
 })
 // []string{"1", "2", "3", "4"}
@@ -132,7 +132,7 @@ present := lo.Contains[int]([]int{0, 1, 2, 3, 4, 5}, 5)
 Reduces collection to a value which is the accumulated result of running each element in collection through accumulator, where each successive invocation is supplied the return value of the previous.
 
 ```go
-sum := lo.Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int) int {
+sum := lo.Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int, _ int) int {
     return agg + item
 }, 0)
 // 10

pointers.go

@@ -7,5 +7,7 @@ func ToPtr[T any](x T) *T {
 
 // ToPtr returns a slice of pointer copy of value.
 func ToSlicePtr[T any](collection []T) []*T {
-	return Map(collection, ToPtr[T])
+	return Map(collection, func (x T, _ int) *T {
+		return &x
+	})
 }

slice.go

@@ -16,30 +16,30 @@ func Filter[V any](collection []V, predicate func(V, int) bool) []V {
 }
 
 // Map manipulates a slice and transforms it to a slice of another type.
-func Map[T any, R any](collection []T, iteratee func(T) R) []R {
+func Map[T any, R any](collection []T, iteratee func(T, int) R) []R {
 	result := make([]R, 0, len(collection))
 
-	for _, item := range collection {
-		result = append(result, iteratee(item))
+	for i, item := range collection {
+		result = append(result, iteratee(item, i))
 	}
 
 	return result
 }
 
 // Reduce reduces collection to a value which is the accumulated result of running each element in collection
 // through accumulator, where each successive invocation is supplied the return value of the previous.
-func Reduce[T any, R any](collection []T, accumulator func(R, T) R, initial R) R {
-	for _, item := range collection {
-		initial = accumulator(initial, item)
+func Reduce[T any, R any](collection []T, accumulator func(R, T, int) R, initial R) R {
+	for i, item := range collection {
+		initial = accumulator(initial, item, i)
 	}
 
 	return initial
 }
 
 // ForEach iterates over elements of collection and invokes iteratee for each element.
-func ForEach[T any](collection []T, iteratee func(T)) {
-	for _, item := range collection {
-		iteratee(item)
+func ForEach[T any](collection []T, iteratee func(T, int)) {
+	for i, item := range collection {
+		iteratee(item, i)
 	}
 }
 

slice_test.go

@@ -26,10 +26,10 @@ func TestFilter(t *testing.T) {
 func TestMap(t *testing.T) {
 	is := assert.New(t)
 
-	result1 := Map[int, string]([]int{1, 2, 3, 4}, func(x int) string {
+	result1 := Map[int, string]([]int{1, 2, 3, 4}, func(x int, _ int) string {
 		return "Hello"
 	})
-	result2 := Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64) string {
+	result2 := Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
 		return strconv.FormatInt(x, 10)
 	})
 
@@ -42,10 +42,10 @@ func TestMap(t *testing.T) {
 func TestReduce(t *testing.T) {
 	is := assert.New(t)
 
-	result1 := Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int) int {
+	result1 := Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int, _ int) int {
 		return agg + item
 	}, 0)
-	result2 := Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int) int {
+	result2 := Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int, _ int) int {
 		return agg + item
 	}, 10)