Add validation for mapper function return type

Signed-off-by: Dinesh <dineshudt17@gmail.com>

Author: dineshba

map.go

@@ -28,9 +28,15 @@ func Map(in, out, mapperFn interface{}) error {
 	}
 
 	if input.Kind() == reflect.Slice {
+		if output.Kind() != reflect.Slice {
+			return fmt.Errorf("output should be a slice for input of type slice")
+		}
 		if input.Type().Elem().Kind() != mapper.Type().In(0).Kind() {
 			return fmt.Errorf("mapper function's first argument has to be the type of element of input slice")
 		}
+		if output.Type().Elem().Elem().Kind() != mapper.Type().Out(0).Kind() {
+			return fmt.Errorf("mapper function's return type has to be the type of element of output slice")
+		}
 
 		result := reflect.MakeSlice(output.Elem().Type(), 0, input.Len())
 		for i := 0; i < input.Len(); i++ {
@@ -46,4 +52,3 @@ func Map(in, out, mapperFn interface{}) error {
 	}
 	return fmt.Errorf("not implemented")
 }
-

map_test.go

@@ -62,6 +62,15 @@ func TestMap(t *testing.T) {
 		}
 	})
 
+	t.Run("should not panic if output is not a slice", func(t *testing.T) {
+		in := []int{1, 2, 3}
+		var out int
+
+		err := godash.Map(in, &out, squared)
+
+		assert.EqualError(t, err, "output should be a slice for input of type slice")
+	})
+
 	t.Run("should not accept mapper function that are not functions", func(t *testing.T) {
 		in := []int{1, 2, 3}
 		var out []int
@@ -115,4 +124,19 @@ func TestMap(t *testing.T) {
 			assert.NoError(t, err)
 		}
 	})
+
+	t.Run("should accept mapper function whose return's kind should be  output slice's element kind", func(t *testing.T) {
+		in := []int{1, 2, 3}
+		var out []string
+
+		{
+			err := godash.Map(in, &out, func(int) int { return 0 })
+			assert.EqualError(t, err, "mapper function's return type has to be the type of element of output slice")
+		}
+
+		{
+			err := godash.Map(in, &out, func(int) string { return "" })
+			assert.NoError(t, err)
+		}
+	})
 }