Add StructValue so we don't need temp slices to pass keys and values

command.go

@@ -374,7 +374,7 @@ func (cmd *SliceCmd) String() string {
 
 // Scan scans the results from the map into a destination struct. The map keys
 // are matched in the Redis struct fields by the `redis:"field"` tag.
-func (cmd *SliceCmd) Scan(dest interface{}) error {
+func (cmd *SliceCmd) Scan(dst interface{}) error {
 	if cmd.err != nil {
 		return cmd.err
 	}
@@ -389,7 +389,7 @@ func (cmd *SliceCmd) Scan(dest interface{}) error {
 		args = cmd.args[1:]
 	}
 
-	return hscan.Scan(args, cmd.val, dest)
+	return hscan.Scan(dst, args, cmd.val)
 }
 
 func (cmd *SliceCmd) readReply(rd *proto.Reader) error {
@@ -940,23 +940,23 @@ func (cmd *StringStringMapCmd) String() string {
 
 // Scan scans the results from the map into a destination struct. The map keys
 // are matched in the Redis struct fields by the `redis:"field"` tag.
-func (cmd *StringStringMapCmd) Scan(dest interface{}) error {
+func (cmd *StringStringMapCmd) Scan(dst interface{}) error {
 	if cmd.err != nil {
 		return cmd.err
 	}
 
-	// Pass the list of keys and values. Skip the first to args (command, key),
-	// eg: HGETALL map.
-	var (
-		keys = make([]interface{}, 0, len(cmd.val))
-		vals = make([]interface{}, 0, len(cmd.val))
-	)
-	for k, v := range cmd.val {
-		keys = append(keys, k)
-		vals = append(vals, v)
+	strct, err := hscan.Struct(dst)
+	if err != nil {
+		return err
 	}
 
-	return hscan.Scan(keys, vals, dest)
+	for k, v := range cmd.val {
+		if err := strct.Scan(k, v); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 func (cmd *StringStringMapCmd) readReply(rd *proto.Reader) error {

internal/hscan/hscan.go

@@ -43,32 +43,39 @@ var (
 	// Global map of struct field specs that is populated once for every new
 	// struct type that is scanned. This caches the field types and the corresponding
 	// decoder functions to avoid iterating through struct fields on subsequent scans.
-	structSpecs = newStructMap()
+	globalStructMap = newStructMap()
 )
 
+func Struct(dst interface{}) (StructValue, error) {
+	v := reflect.ValueOf(dst)
+
+	// The dstination to scan into should be a struct pointer.
+	if v.Kind() != reflect.Ptr || v.IsNil() {
+		return StructValue{}, fmt.Errorf("redis.Scan(non-pointer %T)", dst)
+	}
+
+	v = v.Elem()
+	if v.Kind() != reflect.Struct {
+		return StructValue{}, fmt.Errorf("redis.Scan(non-struct %T)", dst)
+	}
+
+	return StructValue{
+		spec:  globalStructMap.get(v.Type()),
+		value: v,
+	}, nil
+}
+
 // Scan scans the results from a key-value Redis map result set to a destination struct.
 // The Redis keys are matched to the struct's field with the `redis` tag.
-func Scan(keys []interface{}, vals []interface{}, dest interface{}) error {
+func Scan(dst interface{}, keys []interface{}, vals []interface{}) error {
 	if len(keys) != len(vals) {
 		return errors.New("args should have the same number of keys and vals")
 	}
 
-	// The destination to scan into should be a struct pointer.
-	v := reflect.ValueOf(dest)
-	if v.Kind() != reflect.Ptr || v.IsNil() {
-		return fmt.Errorf("redis.Scan(non-pointer %T)", dest)
+	strct, err := Struct(dst)
+	if err != nil {
+		return err
 	}
-	v = v.Elem()
-
-	if v.Kind() != reflect.Struct {
-		return fmt.Errorf("redis.Scan(non-struct %T)", dest)
-	}
-
-	// If the struct field spec is not cached, build and cache it to avoid
-	// iterating through the fields of a struct type every time values are
-	// scanned into it.
-	typ := v.Type()
-	fMap := structSpecs.get(typ)
 
 	// Iterate through the (key, value) sequence.
 	for i := 0; i < len(vals); i++ {
@@ -82,13 +89,7 @@ func Scan(keys []interface{}, vals []interface{}, dest interface{}) error {
 			continue
 		}
 
-		// Check if the field name is in the field spec map.
-		field, ok := fMap.get(key)
-		if !ok {
-			continue
-		}
-
-		if err := field.fn(v.Field(field.index), val); err != nil {
+		if err := strct.Scan(key, val); err != nil {
 			return err
 		}
 	}

internal/hscan/hscan_test.go

@@ -28,33 +28,31 @@ func TestGinkgoSuite(t *testing.T) {
 
 var _ = Describe("Scan", func() {
 	It("catches bad args", func() {
-		var (
-			d data
-		)
+		var d data
 
-		Expect(Scan(i{}, i{}, &d)).NotTo(HaveOccurred())
+		Expect(Scan(&d, i{}, i{})).NotTo(HaveOccurred())
 		Expect(d).To(Equal(data{}))
 
-		Expect(Scan(i{"key"}, i{}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"key"}, i{"1", "2"}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"key", "1"}, i{}, nil)).To(HaveOccurred())
+		Expect(Scan(&d, i{"key"}, i{})).To(HaveOccurred())
+		Expect(Scan(&d, i{"key"}, i{"1", "2"})).To(HaveOccurred())
+		Expect(Scan(nil, i{"key", "1"}, i{})).To(HaveOccurred())
 
 		var m map[string]interface{}
-		Expect(Scan(i{"key"}, i{"1"}, &m)).To(HaveOccurred())
-		Expect(Scan(i{"key"}, i{"1"}, data{})).To(HaveOccurred())
-		Expect(Scan(i{"key", "string"}, i{nil, nil}, data{})).To(HaveOccurred())
+		Expect(Scan(&m, i{"key"}, i{"1"})).To(HaveOccurred())
+		Expect(Scan(data{}, i{"key"}, i{"1"})).To(HaveOccurred())
+		Expect(Scan(data{}, i{"key", "string"}, i{nil, nil})).To(HaveOccurred())
 	})
 
 	It("scans good values", func() {
 		var d data
 
 		// non-tagged fields.
-		Expect(Scan(i{"key"}, i{"value"}, &d)).NotTo(HaveOccurred())
+		Expect(Scan(&d, i{"key"}, i{"value"})).NotTo(HaveOccurred())
 		Expect(d).To(Equal(data{}))
 
 		keys := i{"string", "byte", "int", "uint", "float", "bool"}
 		vals := i{"str!", "bytes!", "123", "456", "123.456", "1"}
-		Expect(Scan(keys, vals, &d)).NotTo(HaveOccurred())
+		Expect(Scan(&d, keys, vals)).NotTo(HaveOccurred())
 		Expect(d).To(Equal(data{
 			String: "str!",
 			Bytes:  []byte("bytes!"),
@@ -75,7 +73,7 @@ var _ = Describe("Scan", func() {
 			Bool   bool    `redis:"bool"`
 		}
 		var d2 data2
-		Expect(Scan(keys, vals, &d2)).NotTo(HaveOccurred())
+		Expect(Scan(&d2, keys, vals)).NotTo(HaveOccurred())
 		Expect(d2).To(Equal(data2{
 			String: "str!",
 			Bytes:  []byte("bytes!"),
@@ -85,7 +83,7 @@ var _ = Describe("Scan", func() {
 			Bool:   true,
 		}))
 
-		Expect(Scan(i{"string", "float", "bool"}, i{"", "1", "t"}, &d)).NotTo(HaveOccurred())
+		Expect(Scan(&d, i{"string", "float", "bool"}, i{"", "1", "t"})).NotTo(HaveOccurred())
 		Expect(d).To(Equal(data{
 			String: "",
 			Bytes:  []byte("bytes!"),
@@ -99,7 +97,7 @@ var _ = Describe("Scan", func() {
 	It("omits untagged fields", func() {
 		var d data
 
-		Expect(Scan(i{"empty", "omit", "string"}, i{"value", "value", "str!"}, &d)).NotTo(HaveOccurred())
+		Expect(Scan(&d, i{"empty", "omit", "string"}, i{"value", "value", "str!"})).NotTo(HaveOccurred())
 		Expect(d).To(Equal(data{
 			String: "str!",
 		}))
@@ -108,12 +106,12 @@ var _ = Describe("Scan", func() {
 	It("catches bad values", func() {
 		var d data
 
-		Expect(Scan(i{"int"}, i{"a"}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"uint"}, i{"a"}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"uint"}, i{""}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"float"}, i{"b"}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"bool"}, i{"-1"}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"bool"}, i{""}, &d)).To(HaveOccurred())
-		Expect(Scan(i{"bool"}, i{"123"}, &d)).To(HaveOccurred())
+		Expect(Scan(&d, i{"int"}, i{"a"})).To(HaveOccurred())
+		Expect(Scan(&d, i{"uint"}, i{"a"})).To(HaveOccurred())
+		Expect(Scan(&d, i{"uint"}, i{""})).To(HaveOccurred())
+		Expect(Scan(&d, i{"float"}, i{"b"})).To(HaveOccurred())
+		Expect(Scan(&d, i{"bool"}, i{"-1"})).To(HaveOccurred())
+		Expect(Scan(&d, i{"bool"}, i{""})).To(HaveOccurred())
+		Expect(Scan(&d, i{"bool"}, i{"123"})).To(HaveOccurred())
 	})
 })

internal/hscan/structmap.go

@@ -6,17 +6,6 @@ import (
 	"sync"
 )
 
-// structField represents a single field in a target struct.
-type structField struct {
-	index int
-	fn    decoderFunc
-}
-
-// structFields contains the list of all fields in a target struct.
-type structFields struct {
-	m map[string]*structField
-}
-
 // structMap contains the map of struct fields for target structs
 // indexed by the struct type.
 type structMap struct {
@@ -27,37 +16,38 @@ func newStructMap() *structMap {
 	return new(structMap)
 }
 
-func (s *structMap) get(t reflect.Type) *structFields {
+func (s *structMap) get(t reflect.Type) *structSpec {
 	if v, ok := s.m.Load(t); ok {
-		return v.(*structFields)
+		return v.(*structSpec)
 	}
 
-	fMap := getStructFields(t, "redis")
-	s.m.Store(t, fMap)
-	return fMap
+	spec := newStructSpec(t, "redis")
+	s.m.Store(t, spec)
+	return spec
 }
 
-func newStructFields() *structFields {
-	return &structFields{
-		m: make(map[string]*structField),
-	}
+//------------------------------------------------------------------------------
+
+// structSpec contains the list of all fields in a target struct.
+type structSpec struct {
+	m map[string]*structField
 }
 
-func (s *structFields) set(tag string, sf *structField) {
+func (s *structSpec) set(tag string, sf *structField) {
 	s.m[tag] = sf
 }
 
-func (s *structFields) get(tag string) (*structField, bool) {
+func (s *structSpec) get(tag string) (*structField, bool) {
 	f, ok := s.m[tag]
 	return f, ok
 }
 
-func getStructFields(t reflect.Type, fieldTag string) *structFields {
-	var (
-		num = t.NumField()
-		out = newStructFields()
-	)
+func newStructSpec(t reflect.Type, fieldTag string) *structSpec {
+	out := &structSpec{
+		m: make(map[string]*structField),
+	}
 
+	num := t.NumField()
 	for i := 0; i < num; i++ {
 		f := t.Field(i)
 
@@ -77,3 +67,26 @@ func getStructFields(t reflect.Type, fieldTag string) *structFields {
 
 	return out
 }
+
+//------------------------------------------------------------------------------
+
+// structField represents a single field in a target struct.
+type structField struct {
+	index int
+	fn    decoderFunc
+}
+
+//------------------------------------------------------------------------------
+
+type StructValue struct {
+	spec  *structSpec
+	value reflect.Value
+}
+
+func (s StructValue) Scan(key string, value string) error {
+	field, ok := s.spec.m[key]
+	if !ok {
+		return nil
+	}
+	return field.fn(s.value.Field(field.index), value)
+}