Add the Var and FlagSet variants for completeness

duration.go

@@ -1,4 +1,8 @@
 // Package duration allows duration parsing with "d" for days (24 hours) and "w" for week (7 days).
+// For output direction, it implements a more human friendly formatting of durations removing
+// all 0 values and using days and weeks when applicable.
+// Includes helpers for command line flag duration parsing and for date/time parsing replacement.
+// See also [fortio.org/dflag] if you need dynamic flags with days/weeks support.
 package duration
 
 import (
@@ -95,6 +99,11 @@ func Parse(s string) (time.Duration, error) {
 	return d, nil
 }
 
+// Duration is like [time.Duration] but supports days (24h) and weeks (7d) in addition to the
+// units supported by [time.Duration]. This is mostly for internal use for the [Flag] function
+// which still returns a standard duration for compatibility. Or if you want the more compact
+// formatting with days and weeks and no zeroes in [Duration.String].
+//
 //nolint:recvcheck // need pointer receiver obviously for Set and for String avoids pointer.
 type Duration time.Duration
 
@@ -185,11 +194,28 @@ func (d *Duration) Set(s string) error {
 
 // Flag defines a duration flag with the specified name, default value, and usage string, like
 // [flag.Duration] but supporting durations in days (24 hours) and weeks (7 days)
-// in addition to the other stdlib units.
+// in addition to the other stdlib units. Replacement for [flag.Duration].
 func Flag(name string, value time.Duration, usage string) *time.Duration {
+	return FlagSet(flag.CommandLine, name, value, usage)
+}
+
+// FlagSet is like [Flag] but for the specified flag set. Replacement for [flag.FlagSet.Duration].
+func FlagSet(fs *flag.FlagSet, name string, value time.Duration, usage string) *time.Duration {
+	p := new(time.Duration)
+	FlagSetVar(fs, p, name, value, usage)
+	return p
+}
+
+// FlagVar is like [Flag] but binds the value to variable referenced. Replacement for [flag.DurationVar].
+func FlagVar(p *time.Duration, name string, value time.Duration, usage string) {
+	FlagSetVar(flag.CommandLine, p, name, value, usage)
+}
+
+// FlagSet is like [FlagVar] but for the specified flag set. Replacement for [flag.FlagSet.DurationVar].
+func FlagSetVar(fs *flag.FlagSet, p *time.Duration, name string, value time.Duration, usage string) {
 	d := Duration(value)
-	flag.Var(&d, name, usage)
-	return (*time.Duration)(&d)
+	fs.Var((*Duration)(p), name, usage)
+	*p = time.Duration(d)
 }
 
 // NextTime takes a partially parsed time.Time (without date) and returns the time in the future

duration_test.go

@@ -80,6 +80,16 @@ func TestFlag(t *testing.T) {
 	}
 }
 
+func TestFlagVar(t *testing.T) {
+	defaultValue, _ := duration.Parse("1d3m")
+	var d time.Duration
+	duration.FlagVar(&d, "test2", defaultValue, "test `duration`")
+	flag.Lookup("test2").Value.Set("1d1h")
+	if d != 25*time.Hour {
+		t.Errorf("Expected 25h but got %v", d)
+	}
+}
+
 func TestParseDateTime(t *testing.T) {
 	l, err := time.LoadLocation("America/New_York")
 	if err != nil {
@@ -147,7 +157,7 @@ func TestParseDateTimeIsLocal(t *testing.T) {
 	}
 }
 
-func Example() {
+func ExampleParse() {
 	d, err := duration.Parse("1w 2d 3h 4m")
 	if err != nil {
 		fmt.Println("Error:", err)
@@ -159,3 +169,19 @@ func Example() {
 	// Parsed duration (std): 219h4m0s
 	// Parsed duration (new): 1w2d3h4m
 }
+
+func ExampleFlag() {
+	f := duration.Flag("duration-flag", 1*duration.Day, "test `duration`")
+	// and then use *f normally and the users can use days, weeks etc.
+
+	// to test/show:
+	flv := flag.Lookup("duration-flag").Value
+	fmt.Println("Default:", flv.String())
+	flv.Set("1d1h") // no error
+	fmt.Println("After set:", flv.String())
+	fmt.Println("After set (dereferenced):", *f)
+	// Output:
+	// Default: 1d
+	// After set: 1d1h
+	// After set (dereferenced): 25h0m0s
+}