24 files changed, 635 insertions, 0 deletions

diff --git a/bool_slice.go b/bool_slice.go
index 5af02f1..3731370 100644
--- a/bool_slice.go
+++ b/bool_slice.go
@@ -71,6 +71,44 @@ func (s *boolSliceValue) String() string {
 	return "[" + out + "]"
 }
 
+func (s *boolSliceValue) fromString(val string) (bool, error) {
+	return strconv.ParseBool(val)
+}
+
+func (s *boolSliceValue) toString(val bool) string {
+	return strconv.FormatBool(val)
+}
+
+func (s *boolSliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *boolSliceValue) Replace(val []string) error {
+	out := make([]bool, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *boolSliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func boolSliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/bool_slice_test.go b/bool_slice_test.go
index b617dd2..3c5a274 100644
--- a/bool_slice_test.go
+++ b/bool_slice_test.go
@@ -160,6 +160,29 @@ func TestBSCalledTwice(t *testing.T) {
 	}
 }
 
+func TestBSAsSliceValue(t *testing.T) {
+	var bs []bool
+	f := setUpBSFlagSet(&bs)
+
+	in := []string{"true", "false"}
+	argfmt := "--bs=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"false"})
+		}
+	})
+	if len(bs) != 1 || bs[0] != false {
+		t.Fatalf("Expected ss to be overwritten with 'false', but got: %v", bs)
+	}
+}
+
 func TestBSBadQuoting(t *testing.T) {
 
 	tests := []struct {
diff --git a/duration_slice.go b/duration_slice.go
index 52c6b6d..badadda 100644
--- a/duration_slice.go
+++ b/duration_slice.go
@@ -51,6 +51,44 @@ func (s *durationSliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *durationSliceValue) fromString(val string) (time.Duration, error) {
+	return time.ParseDuration(val)
+}
+
+func (s *durationSliceValue) toString(val time.Duration) string {
+	return fmt.Sprintf("%s", val)
+}
+
+func (s *durationSliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *durationSliceValue) Replace(val []string) error {
+	out := make([]time.Duration, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *durationSliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func durationSliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/duration_slice_test.go b/duration_slice_test.go
index 489b012..651fbd8 100644
--- a/duration_slice_test.go
+++ b/duration_slice_test.go
@@ -144,6 +144,29 @@ func TestDSWithDefault(t *testing.T) {
 	}
 }
 
+func TestDSAsSliceValue(t *testing.T) {
+	var ds []time.Duration
+	f := setUpDSFlagSet(&ds)
+
+	in := []string{"1ns", "2ns"}
+	argfmt := "--ds=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3ns"})
+		}
+	})
+	if len(ds) != 1 || ds[0] != time.Duration(3) {
+		t.Fatalf("Expected ss to be overwritten with '3ns', but got: %v", ds)
+	}
+}
+
 func TestDSCalledTwice(t *testing.T) {
 	var ds []time.Duration
 	f := setUpDSFlagSet(&ds)
diff --git a/flag.go b/flag.go
index 669c392..24a5036 100644
--- a/flag.go
+++ b/flag.go
@@ -190,6 +190,18 @@ type Value interface {
 	Type() string
 }
 
+// SliceValue is a secondary interface to all flags which hold a list
+// of values.  This allows full control over the value of list flags,
+// and avoids complicated marshalling and unmarshalling to csv.
+type SliceValue interface {
+	// Append adds the specified value to the end of the flag value list.
+	Append(string) error
+	// Replace will fully overwrite any data currently in the flag value list.
+	Replace([]string) error
+	// GetSlice returns the flag value list as an array of strings.
+	GetSlice() []string
+}
+
 // sortFlags returns the flags as a slice in lexicographical sorted order.
 func sortFlags(flags map[NormalizedName]*Flag) []*Flag {
 	list := make(sort.StringSlice, len(flags))
diff --git a/float32_slice.go b/float32_slice.go
index a80848a..caa3527 100644
--- a/float32_slice.go
+++ b/float32_slice.go
@@ -53,6 +53,48 @@ func (s *float32SliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *float32SliceValue) fromString(val string) (float32, error) {
+	t64, err := strconv.ParseFloat(val, 32)
+	if err != nil {
+		return 0, err
+	}
+	return float32(t64), nil
+}
+
+func (s *float32SliceValue) toString(val float32) string {
+	return fmt.Sprintf("%f", val)
+}
+
+func (s *float32SliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *float32SliceValue) Replace(val []string) error {
+	out := make([]float32, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *float32SliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func float32SliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/float32_slice_test.go b/float32_slice_test.go
index 2429c8f..997ce5c 100644
--- a/float32_slice_test.go
+++ b/float32_slice_test.go
@@ -156,6 +156,29 @@ func TestF32SWithDefault(t *testing.T) {
 	}
 }
 
+func TestF32SAsSliceValue(t *testing.T) {
+	var f32s []float32
+	f := setUpF32SFlagSet(&f32s)
+
+	in := []string{"1.0", "2.0"}
+	argfmt := "--f32s=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3.1"})
+		}
+	})
+	if len(f32s) != 1 || f32s[0] != 3.1 {
+		t.Fatalf("Expected ss to be overwritten with '3.1', but got: %v", f32s)
+	}
+}
+
 func TestF32SCalledTwice(t *testing.T) {
 	var f32s []float32
 	f := setUpF32SFlagSet(&f32s)
diff --git a/float64_slice.go b/float64_slice.go
index 45d12b8..85bf307 100644
--- a/float64_slice.go
+++ b/float64_slice.go
@@ -51,6 +51,44 @@ func (s *float64SliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *float64SliceValue) fromString(val string) (float64, error) {
+	return strconv.ParseFloat(val, 64)
+}
+
+func (s *float64SliceValue) toString(val float64) string {
+	return fmt.Sprintf("%f", val)
+}
+
+func (s *float64SliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *float64SliceValue) Replace(val []string) error {
+	out := make([]float64, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *float64SliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func float64SliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/float64_slice_test.go b/float64_slice_test.go
index fe9ede4..43778ef 100644
--- a/float64_slice_test.go
+++ b/float64_slice_test.go
@@ -144,6 +144,29 @@ func TestF64SWithDefault(t *testing.T) {
 	}
 }
 
+func TestF64SAsSliceValue(t *testing.T) {
+	var f64s []float64
+	f := setUpF64SFlagSet(&f64s)
+
+	in := []string{"1.0", "2.0"}
+	argfmt := "--f64s=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3.1"})
+		}
+	})
+	if len(f64s) != 1 || f64s[0] != 3.1 {
+		t.Fatalf("Expected ss to be overwritten with '3.1', but got: %v", f64s)
+	}
+}
+
 func TestF64SCalledTwice(t *testing.T) {
 	var f64s []float64
 	f := setUpF64SFlagSet(&f64s)
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..7eb892e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module github.com/spf13/pflags
+
+go 1.12
+
+require github.com/spf13/pflag v1.0.3
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..edd0bcf
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
+github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
diff --git a/int32_slice.go b/int32_slice.go
index 6ccedcc..ff128ff 100644
--- a/int32_slice.go
+++ b/int32_slice.go
@@ -53,6 +53,48 @@ func (s *int32SliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *int32SliceValue) fromString(val string) (int32, error) {
+	t64, err := strconv.ParseInt(val, 0, 32)
+	if err != nil {
+		return 0, err
+	}
+	return int32(t64), nil
+}
+
+func (s *int32SliceValue) toString(val int32) string {
+	return fmt.Sprintf("%d", val)
+}
+
+func (s *int32SliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *int32SliceValue) Replace(val []string) error {
+	out := make([]int32, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *int32SliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func int32SliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/int32_slice_test.go b/int32_slice_test.go
index 69aaf9b..809c563 100644
--- a/int32_slice_test.go
+++ b/int32_slice_test.go
@@ -150,6 +150,29 @@ func TestI32SWithDefault(t *testing.T) {
 	}
 }
 
+func TestI32SAsSliceValue(t *testing.T) {
+	var i32s []int32
+	f := setUpI32SFlagSet(&i32s)
+
+	in := []string{"1", "2"}
+	argfmt := "--is=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3"})
+		}
+	})
+	if len(i32s) != 1 || i32s[0] != 3 {
+		t.Fatalf("Expected ss to be overwritten with '3.1', but got: %v", i32s)
+	}
+}
+
 func TestI32SCalledTwice(t *testing.T) {
 	var is []int32
 	f := setUpI32SFlagSet(&is)
diff --git a/int64_slice.go b/int64_slice.go
index 86cb619..2546463 100644
--- a/int64_slice.go
+++ b/int64_slice.go
@@ -51,6 +51,44 @@ func (s *int64SliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *int64SliceValue) fromString(val string) (int64, error) {
+	return strconv.ParseInt(val, 0, 64)
+}
+
+func (s *int64SliceValue) toString(val int64) string {
+	return fmt.Sprintf("%d", val)
+}
+
+func (s *int64SliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *int64SliceValue) Replace(val []string) error {
+	out := make([]int64, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *int64SliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func int64SliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/int64_slice_test.go b/int64_slice_test.go
index b536943..09805c7 100644
--- a/int64_slice_test.go
+++ b/int64_slice_test.go
@@ -144,6 +144,29 @@ func TestI64SWithDefault(t *testing.T) {
 	}
 }
 
+func TestI64SAsSliceValue(t *testing.T) {
+	var i64s []int64
+	f := setUpI64SFlagSet(&i64s)
+
+	in := []string{"1", "2"}
+	argfmt := "--is=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3"})
+		}
+	})
+	if len(i64s) != 1 || i64s[0] != 3 {
+		t.Fatalf("Expected ss to be overwritten with '3.1', but got: %v", i64s)
+	}
+}
+
 func TestI64SCalledTwice(t *testing.T) {
 	var is []int64
 	f := setUpI64SFlagSet(&is)
diff --git a/int_slice.go b/int_slice.go
index 1e7c9ed..e71c39d 100644
--- a/int_slice.go
+++ b/int_slice.go
@@ -51,6 +51,36 @@ func (s *intSliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *intSliceValue) Append(val string) error {
+	i, err := strconv.Atoi(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *intSliceValue) Replace(val []string) error {
+	out := make([]int, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = strconv.Atoi(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *intSliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = strconv.Itoa(d)
+	}
+	return out
+}
+
 func intSliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/ip_slice.go b/ip_slice.go
index 6ad2e92..775faae 100644
--- a/ip_slice.go
+++ b/ip_slice.go
@@ -72,6 +72,44 @@ func (s *ipSliceValue) String() string {
 	return "[" + out + "]"
 }
 
+func (s *ipSliceValue) fromString(val string) (net.IP, error) {
+	return net.ParseIP(strings.TrimSpace(val)), nil
+}
+
+func (s *ipSliceValue) toString(val net.IP) string {
+	return val.String()
+}
+
+func (s *ipSliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *ipSliceValue) Replace(val []string) error {
+	out := make([]net.IP, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *ipSliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func ipSliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/ip_slice_test.go b/ip_slice_test.go
index b0c681c..d189276 100644
--- a/ip_slice_test.go
+++ b/ip_slice_test.go
@@ -141,6 +141,29 @@ func TestIPSCalledTwice(t *testing.T) {
 	}
 }
 
+func TestIPSAsSliceValue(t *testing.T) {
+	var ips []net.IP
+	f := setUpIPSFlagSet(&ips)
+
+	in := []string{"192.168.1.1", "0:0:0:0:0:0:0:1"}
+	argfmt := "--ips=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"192.168.1.2"})
+		}
+	})
+	if len(ips) != 1 || !ips[0].Equal(net.ParseIP("192.168.1.2")) {
+		t.Fatalf("Expected ss to be overwritten with '192.168.1.2', but got: %v", ips)
+	}
+}
+
 func TestIPSBadQuoting(t *testing.T) {
 
 	tests := []struct {
diff --git a/string_array.go b/string_array.go
index fa7bc60..4894af8 100644
--- a/string_array.go
+++ b/string_array.go
@@ -23,6 +23,32 @@ func (s *stringArrayValue) Set(val string) error {
 	return nil
 }
 
+func (s *stringArrayValue) Append(val string) error {
+	*s.value = append(*s.value, val)
+	return nil
+}
+
+func (s *stringArrayValue) Replace(val []string) error {
+	out := make([]string, len(val))
+	for i, d := range val {
+		var err error
+		out[i] = d
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *stringArrayValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = d
+	}
+	return out
+}
+
 func (s *stringArrayValue) Type() string {
 	return "stringArray"
 }
diff --git a/string_array_test.go b/string_array_test.go
index 1ceac8c..3c6d595 100644
--- a/string_array_test.go
+++ b/string_array_test.go
@@ -193,6 +193,29 @@ func TestSAWithSpecialChar(t *testing.T) {
 	}
 }
 
+func TestSAAsSliceValue(t *testing.T) {
+	var sa []string
+	f := setUpSAFlagSet(&sa)
+
+	in := []string{"1ns", "2ns"}
+	argfmt := "--sa=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3ns"})
+		}
+	})
+	if len(sa) != 1 || sa[0] != "3ns" {
+		t.Fatalf("Expected ss to be overwritten with '3ns', but got: %v", sa)
+	}
+}
+
 func TestSAWithSquareBrackets(t *testing.T) {
 	var sa []string
 	f := setUpSAFlagSet(&sa)
diff --git a/string_slice.go b/string_slice.go
index b816ca8..3cb2e69 100644
--- a/string_slice.go
+++ b/string_slice.go
@@ -62,6 +62,20 @@ func (s *stringSliceValue) String() string {
 	return "[" + str + "]"
 }
 
+func (s *stringSliceValue) Append(val string) error {
+	*s.value = append(*s.value, val)
+	return nil
+}
+
+func (s *stringSliceValue) Replace(val []string) error {
+	*s.value = val
+	return nil
+}
+
+func (s *stringSliceValue) GetSlice() []string {
+	return *s.value
+}
+
 func stringSliceConv(sval string) (interface{}, error) {
 	sval = sval[1 : len(sval)-1]
 	// An empty string would cause a slice with one (empty) string
diff --git a/string_slice_test.go b/string_slice_test.go
index c41f3bd..9692461 100644
--- a/string_slice_test.go
+++ b/string_slice_test.go
@@ -251,3 +251,26 @@ func TestSSWithSquareBrackets(t *testing.T) {
 		}
 	}
 }
+
+func TestSSAsSliceValue(t *testing.T) {
+	var ss []string
+	f := setUpSSFlagSet(&ss)
+
+	in := []string{"one", "two"}
+	argfmt := "--ss=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"three"})
+		}
+	})
+	if len(ss) != 1 || ss[0] != "three" {
+		t.Fatalf("Expected ss to be overwritten with 'three', but got: %s", ss)
+	}
+}
diff --git a/uint_slice.go b/uint_slice.go
index edd94c6..5fa9248 100644
--- a/uint_slice.go
+++ b/uint_slice.go
@@ -50,6 +50,48 @@ func (s *uintSliceValue) String() string {
 	return "[" + strings.Join(out, ",") + "]"
 }
 
+func (s *uintSliceValue) fromString(val string) (uint, error) {
+	t, err := strconv.ParseUint(val, 10, 0)
+	if err != nil {
+		return 0, err
+	}
+	return uint(t), nil
+}
+
+func (s *uintSliceValue) toString(val uint) string {
+	return fmt.Sprintf("%d", val)
+}
+
+func (s *uintSliceValue) Append(val string) error {
+	i, err := s.fromString(val)
+	if err != nil {
+		return err
+	}
+	*s.value = append(*s.value, i)
+	return nil
+}
+
+func (s *uintSliceValue) Replace(val []string) error {
+	out := make([]uint, len(val))
+	for i, d := range val {
+		var err error
+		out[i], err = s.fromString(d)
+		if err != nil {
+			return err
+		}
+	}
+	*s.value = out
+	return nil
+}
+
+func (s *uintSliceValue) GetSlice() []string {
+	out := make([]string, len(*s.value))
+	for i, d := range *s.value {
+		out[i] = s.toString(d)
+	}
+	return out
+}
+
 func uintSliceConv(val string) (interface{}, error) {
 	val = strings.Trim(val, "[]")
 	// Empty string would cause a slice with one (empty) entry
diff --git a/uint_slice_test.go b/uint_slice_test.go
index db1a19d..d0da4d0 100644
--- a/uint_slice_test.go
+++ b/uint_slice_test.go
@@ -140,6 +140,29 @@ func TestUISWithDefault(t *testing.T) {
 	}
 }
 
+func TestUISAsSliceValue(t *testing.T) {
+	var uis []uint
+	f := setUpUISFlagSet(&uis)
+
+	in := []string{"1", "2"}
+	argfmt := "--uis=%s"
+	arg1 := fmt.Sprintf(argfmt, in[0])
+	arg2 := fmt.Sprintf(argfmt, in[1])
+	err := f.Parse([]string{arg1, arg2})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+
+	f.VisitAll(func(f *Flag) {
+		if val, ok := f.Value.(SliceValue); ok {
+			_ = val.Replace([]string{"3"})
+		}
+	})
+	if len(uis) != 1 || uis[0] != 3 {
+		t.Fatalf("Expected ss to be overwritten with '3.1', but got: %v", uis)
+	}
+}
+
 func TestUISCalledTwice(t *testing.T) {
 	var uis []uint
 	f := setUpUISFlagSet(&uis)