Add simple Key function for slice functions

...where the key and element types are the same, eg string, int etc.
This saves the caller having to do:

  func(e string) string {
      return e
  }

Signed-off-by: Tom Pantelis <[email protected]>

pkg/slices/slices.go

@@ -98,3 +98,7 @@ func mapFrom[E any, K comparable](s []E, key func(E) K) map[K]bool {
 
 	return m
 }
+
+func Key[K comparable](k K) K {
+	return k
+}

pkg/slices/slices_test.go

@@ -32,7 +32,7 @@ type Status struct {
 var _ = Describe("Intersect", func() {
 	Specify("with non-empty slices", func() {
 		testIntersect := func(s1, s2 []string, exp ...string) {
-			actual := slices.Intersect(s1, s2, key)
+			actual := slices.Intersect(s1, s2, slices.Key[string])
 			Expect(set.New(actual...).Equal(set.New(exp...))).To(BeTrue(), "Expected: %s. Actual: %s", exp, actual)
 		}
 
@@ -45,16 +45,16 @@ var _ = Describe("Intersect", func() {
 	})
 
 	Specify("with empty an slice", func() {
-		Expect(slices.Intersect([]string{"1"}, []string{}, key)).To(BeEmpty())
-		Expect(slices.Intersect([]string{"1"}, nil, key)).To(BeEmpty())
-		Expect(slices.Intersect([]string{}, []string{"1"}, key)).To(BeEmpty())
-		Expect(slices.Intersect(nil, []string{"1"}, key)).To(BeEmpty())
+		Expect(slices.Intersect([]string{"1"}, []string{}, slices.Key[string])).To(BeEmpty())
+		Expect(slices.Intersect([]string{"1"}, nil, slices.Key[string])).To(BeEmpty())
+		Expect(slices.Intersect([]string{}, []string{"1"}, slices.Key[string])).To(BeEmpty())
+		Expect(slices.Intersect(nil, []string{"1"}, slices.Key[string])).To(BeEmpty())
 	})
 })
 
 var _ = Specify("Union", func() {
 	testUnion := func(s1, s2 []string, exp ...string) {
-		actual := slices.Union(s1, s2, key)
+		actual := slices.Union(s1, s2, slices.Key[string])
 		Expect(actual).To(Equal(exp))
 	}
 
@@ -173,10 +173,6 @@ var _ = Describe("Equivalent", func() {
 	})
 })
 
-func key(e string) string {
-	return e
-}
-
 func statusKey(s Status) string {
 	return s.Name
 }