add the Fix field for Opt

config_test.go

@@ -20,6 +20,30 @@ import (
 	"testing"
 )
 
+func ExampleOpt_F() {
+	fix := func(v interface{}) (interface{}, error) { return v.(int) + 1, nil }
+	opt1 := IntOpt("opt1", "test fix with default").D(10).F(fix, true)
+	opt2 := IntOpt("opt2", "test fix without default").D(20).F(fix)
+
+	conf := New()
+	conf.RegisterOpts([]Opt{opt1, opt2})
+
+	fmt.Printf("opt1=%s\n", conf.MustString("opt1"))
+	fmt.Printf("opt2=%s\n", conf.MustString("opt2"))
+
+	conf.UpdateValue("opt1", 30)
+	conf.UpdateValue("opt2", 40)
+
+	fmt.Printf("opt1=%s\n", conf.MustString("opt1"))
+	fmt.Printf("opt2=%s\n", conf.MustString("opt2"))
+
+	// Output:
+	// opt1=11
+	// opt2=20
+	// opt1=31
+	// opt2=41
+}
+
 func TestOptObserver(t *testing.T) {
 	var value string
 	opt := StrOpt("opt", "").D("abc").O(func(v interface{}) { value = v.(string) })

group.go

@@ -331,7 +331,9 @@ func (g *OptGroup) setOptWatch(name string, watch func(interface{})) {
 
 func (g *OptGroup) registerOpt(opt Opt, force ...bool) (ok bool) {
 	opt.check()
-	if err := opt.validate(opt.Default); err != nil {
+	if err := opt.fix(); err != nil {
+		panic(NewOptError(g.name, opt.Name, err, opt.Default))
+	} else if err := opt.validate(opt.Default); err != nil {
 		panic(NewOptError(g.name, opt.Name, err, opt.Default))
 	}
 
@@ -361,7 +363,9 @@ func (g *OptGroup) registerOpts(opts []Opt, force ...bool) (ok bool) {
 	names := make([]string, len(opts))
 	for i := range opts {
 		opts[i].check()
-		if err := opts[i].validate(opts[i].Default); err != nil {
+		if err := opts[i].fix(); err != nil {
+			panic(NewOptError(g.name, opts[i].Name, err, opts[i].Default))
+		} else if err := opts[i].validate(opts[i].Default); err != nil {
 			panic(NewOptError(g.name, opts[i].Name, err, opts[i].Default))
 		}
 		names[i] = g.fixOptName(opts[i].Name)
@@ -535,6 +539,15 @@ func (g *OptGroup) parseOptValue(name string, value interface{}) (interface{}, e
 		return nil, NewOptError(g.name, opt.opt.Name, err, value)
 	}
 
+	// Fix the parsed value
+	if opt.opt.Fix != nil {
+		_v, err := opt.opt.Fix(v)
+		if err != nil {
+			return nil, NewOptError(g.name, opt.opt.Name, err, v)
+		}
+		v = _v
+	}
+
 	// Validate the option value
 	if err = opt.opt.validate(v); err != nil {
 		return nil, NewOptError(g.name, opt.opt.Name, err, v)

opt.go

@@ -56,6 +56,17 @@ type Opt struct {
 	// Notice: it must not panic.
 	Parser func(input interface{}) (output interface{}, err error)
 
+	// Fix is used to fix the parsed value.
+	//
+	// The different between Parser and Fix:
+	//   1. Parser only parses the value from the arbitrary type to a specific.
+	//   2. Fix only changes the value, not the type, that's, input and output
+	//      should be the same type. For example, input is the NIC name,
+	//      and Fix can get the ip by the NIC name then return it as output.
+	//      So it ensures that input may be NIC or IP, and that the value
+	//      of the option is always a IP.
+	Fix func(input interface{}) (output interface{}, err error)
+
 	// Observers are called after the value of the option is updated.
 	Observers []func(newValue interface{})
 
@@ -67,6 +78,8 @@ type Opt struct {
 	//
 	// Notice: they must not panic.
 	Validators []Validator
+
+	fixDefault bool
 }
 
 func (o Opt) check() {
@@ -118,6 +131,30 @@ func (o Opt) D(_default interface{}) Opt {
 	return o
 }
 
+func (o *Opt) fix() error {
+	if o.fixDefault && o.Fix != nil && o.Default != nil {
+		_default, err := o.Fix(o.Default)
+		if err != nil {
+			return err
+		}
+		o.Default = _default
+	}
+	return nil
+}
+
+// F returns a new Opt with the given fix function based on the current option.
+//
+// If fixDefault is true, it will fix the default value when registering
+// the option.
+func (o Opt) F(fix func(interface{}) (interface{}, error), fixDefault ...bool) Opt {
+	o.Fix = fix
+	if len(fixDefault) > 0 {
+		o.fixDefault = fixDefault[0]
+	}
+
+	return o
+}
+
 // H returns a new Opt with the given help based on the current option.
 func (o Opt) H(help string) Opt {
 	o.Help = help