From ba8bbb219a578f8c2ba717784d4b5a57e6e192ce Mon Sep 17 00:00:00 2001
From: Chris Pappas <chris.pappas@shopify.com>
Date: Tue, 23 Aug 2022 09:16:02 -0500
Subject: [PATCH 1/3] Add maps.ToKeys method

- also suppress gosec warnings for rand.Int() calls
---
 maps/maps.go      |  8 ++++++++
 maps/maps_test.go | 29 +++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/maps/maps.go b/maps/maps.go
index ad112e7..bed1dc1 100644
--- a/maps/maps.go
+++ b/maps/maps.go
@@ -18,3 +18,11 @@ func ToSlice[M ~map[K]V, K comparable, V, R any](items M, f func(K, V) R) []R {
 	}
 	return out
 }
+
+func ToKeys[In any, Key comparable](arr map[Key]In) []Key {
+	out := make([]Key, 0, len(arr))
+	for key := range arr {
+		out = append(out, key)
+	}
+	return out
+}
diff --git a/maps/maps_test.go b/maps/maps_test.go
index 8fcd495..f73699c 100644
--- a/maps/maps_test.go
+++ b/maps/maps_test.go
@@ -13,6 +13,31 @@ const benchmarkArrayLength = 10_000
 
 var benchResult []int
 
+func TestToKeys(t *testing.T) {
+	t.Run(
+		"String Keys", func(t *testing.T) {
+			test := map[string]int{
+				"one":   1,
+				"two":   2,
+				"three": 3,
+			}
+			keys := ToKeys(test)
+			require.ElementsMatch(t, []string{"one", "two", "three"}, keys)
+		},
+	)
+	t.Run(
+		"Int Keys", func(t *testing.T) {
+			test := map[int]string{
+				1: "one",
+				2: "two",
+				3: "three",
+			}
+			keys := ToKeys(test)
+			require.ElementsMatch(t, []int{1, 2, 3}, keys)
+		},
+	)
+}
+
 func TestToValues(t *testing.T) {
 	nums := map[string]int{
 		"one":   1,
@@ -44,7 +69,7 @@ func TestToSlice(t *testing.T) {
 func BenchmarkToValues(b *testing.B) {
 	arr := make(map[int]int, benchmarkArrayLength)
 	for i := range arr {
-		arr[i] = rand.Int()
+		arr[i] = rand.Int() //nolint:gosec
 	}
 
 	var r []int
@@ -57,7 +82,7 @@ func BenchmarkToValues(b *testing.B) {
 func BenchmarkToSlice(b *testing.B) {
 	arr := make(map[int]int, benchmarkArrayLength)
 	for i := range arr {
-		arr[i] = rand.Int()
+		arr[i] = rand.Int() //nolint:gosec
 	}
 	var r []int
 	for i := 0; i < b.N; i++ {

From f735e36a83e567dbabc0da43e1465ab6bf8e6773 Mon Sep 17 00:00:00 2001
From: Chris Pappas <chris.pappas@shopify.com>
Date: Tue, 23 Aug 2022 09:26:50 -0500
Subject: [PATCH 2/3] Make it even more efficient without using append

- since we already know the size, we can just pre-allocate and directly access the index
---
 maps/maps.go | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/maps/maps.go b/maps/maps.go
index bed1dc1..80f3a6e 100644
--- a/maps/maps.go
+++ b/maps/maps.go
@@ -2,9 +2,11 @@ package maps
 
 // ToValues returns an array of just the values of the input Map.
 func ToValues[In any, Key comparable](arr map[Key]In) []In {
-	out := make([]In, 0, len(arr))
-	for _, elem := range arr {
-		out = append(out, elem)
+	i := 0
+	out := make([]In, len(arr))
+	for _, value := range arr {
+		out[i] = value
+		i++
 	}
 	return out
 }
@@ -12,17 +14,21 @@ func ToValues[In any, Key comparable](arr map[Key]In) []In {
 // ToSlice applies the function to each element of the input map, and returns an
 // array of the results.
 func ToSlice[M ~map[K]V, K comparable, V, R any](items M, f func(K, V) R) []R {
-	out := make([]R, 0, len(items))
+	i := 0
+	out := make([]R, len(items))
 	for k, v := range items {
-		out = append(out, f(k, v))
+		out[i] = f(k, v)
+		i++
 	}
 	return out
 }
 
 func ToKeys[In any, Key comparable](arr map[Key]In) []Key {
-	out := make([]Key, 0, len(arr))
+	i := 0
+	out := make([]Key, len(arr))
 	for key := range arr {
-		out = append(out, key)
+		out[i] = key
+		i++
 	}
 	return out
 }

From f07a92e130ed940391ddfc0064ebce8e4eb8b451 Mon Sep 17 00:00:00 2001
From: Chris Pappas <chris.pappas@shopify.com>
Date: Thu, 1 Sep 2022 09:23:10 -0500
Subject: [PATCH 3/3] Add missing docs and example test

---
 maps/maps.go      |  1 +
 maps/maps_test.go | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/maps/maps.go b/maps/maps.go
index 80f3a6e..2d01703 100644
--- a/maps/maps.go
+++ b/maps/maps.go
@@ -23,6 +23,7 @@ func ToSlice[M ~map[K]V, K comparable, V, R any](items M, f func(K, V) R) []R {
 	return out
 }
 
+// ToKeys returns an array of the keys of the input Map.
 func ToKeys[In any, Key comparable](arr map[Key]In) []Key {
 	i := 0
 	out := make([]Key, len(arr))
diff --git a/maps/maps_test.go b/maps/maps_test.go
index f73699c..df2a94c 100644
--- a/maps/maps_test.go
+++ b/maps/maps_test.go
@@ -119,3 +119,16 @@ func ExampleToSlice() {
 	fmt.Println(results)
 	// Output: [1 in text is one 2 in text is two 3 in text is three]
 }
+
+func ExampleToKeys() {
+	nums := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	results := ToKeys(nums)
+
+	sort.Strings(results) // order is not guaranteed for map keys
+	fmt.Println(results)
+	// Output: [a b c]
+}