flag: add Getter interface; implement for all Value types

Fixes golang#5383.

R=golang-dev, 0xjnml, r, rsc
CC=golang-dev
https://golang.org/cl/10472043

doc/go1.2.txt

@@ -17,6 +17,7 @@ crypto/sha1: Sum function to simplify hashing (CL 10571043).
 crypto/sha256: Sum256 and Sum224 functions to simplify hashing (CL 10629043).
 crypto/sha512: Sum512 and Sum384 functions to simplify hashing (CL 10630043).
 crypto/tls: add support for TLS 1.1. (CL 7872043).
+flag: add Getter interface (CL 10472043).
 fmt: indexed access to arguments in Printf etc. (CL 9680043).
 go/build: support including C++ code with cgo (CL 8248043).
 io: Copy prioritizes WriterTo over ReaderFrom (CL 9462044).

src/pkg/flag/flag.go

@@ -89,6 +89,8 @@ func (b *boolValue) Set(s string) error {
 	return err
 }
 
+func (b *boolValue) Get() interface{} { return bool(*b) }
+
 func (b *boolValue) String() string { return fmt.Sprintf("%v", *b) }
 
 func (b *boolValue) IsBoolFlag() bool { return true }
@@ -114,6 +116,8 @@ func (i *intValue) Set(s string) error {
 	return err
 }
 
+func (i *intValue) Get() interface{} { return int(*i) }
+
 func (i *intValue) String() string { return fmt.Sprintf("%v", *i) }
 
 // -- int64 Value
@@ -130,6 +134,8 @@ func (i *int64Value) Set(s string) error {
 	return err
 }
 
+func (i *int64Value) Get() interface{} { return int64(*i) }
+
 func (i *int64Value) String() string { return fmt.Sprintf("%v", *i) }
 
 // -- uint Value
@@ -146,6 +152,8 @@ func (i *uintValue) Set(s string) error {
 	return err
 }
 
+func (i *uintValue) Get() interface{} { return uint(*i) }
+
 func (i *uintValue) String() string { return fmt.Sprintf("%v", *i) }
 
 // -- uint64 Value
@@ -162,6 +170,8 @@ func (i *uint64Value) Set(s string) error {
 	return err
 }
 
+func (i *uint64Value) Get() interface{} { return uint64(*i) }
+
 func (i *uint64Value) String() string { return fmt.Sprintf("%v", *i) }
 
 // -- string Value
@@ -177,6 +187,8 @@ func (s *stringValue) Set(val string) error {
 	return nil
 }
 
+func (s *stringValue) Get() interface{} { return string(*s) }
+
 func (s *stringValue) String() string { return fmt.Sprintf("%s", *s) }
 
 // -- float64 Value
@@ -193,6 +205,8 @@ func (f *float64Value) Set(s string) error {
 	return err
 }
 
+func (f *float64Value) Get() interface{} { return float64(*f) }
+
 func (f *float64Value) String() string { return fmt.Sprintf("%v", *f) }
 
 // -- time.Duration Value
@@ -209,6 +223,8 @@ func (d *durationValue) Set(s string) error {
 	return err
 }
 
+func (d *durationValue) Get() interface{} { return time.Duration(*d) }
+
 func (d *durationValue) String() string { return (*time.Duration)(d).String() }
 
 // Value is the interface to the dynamic value stored in a flag.
@@ -222,6 +238,15 @@ type Value interface {
 	Set(string) error
 }
 
+// Getter is an interface that allows the contents of a Value to be retrieved.
+// It wraps the Value interface, rather than being part of it, because it
+// appeared after Go 1 and its compatibility rules. All Value types provided
+// by this package satisfy the Getter interface.
+type Getter interface {
+	Value
+	Get() interface{}
+}
+
 // ErrorHandling defines how to handle flag parsing errors.
 type ErrorHandling int
 

src/pkg/flag/flag_test.go

@@ -92,6 +92,50 @@ func TestEverything(t *testing.T) {
 	}
 }
 
+func TestGet(t *testing.T) {
+	ResetForTesting(nil)
+	Bool("test_bool", true, "bool value")
+	Int("test_int", 1, "int value")
+	Int64("test_int64", 2, "int64 value")
+	Uint("test_uint", 3, "uint value")
+	Uint64("test_uint64", 4, "uint64 value")
+	String("test_string", "5", "string value")
+	Float64("test_float64", 6, "float64 value")
+	Duration("test_duration", 7, "time.Duration value")
+
+	visitor := func(f *Flag) {
+		if len(f.Name) > 5 && f.Name[0:5] == "test_" {
+			g, ok := f.Value.(Getter)
+			if !ok {
+				t.Errorf("Visit: value does not satisfy Getter: %T", f.Value)
+				return
+			}
+			switch f.Name {
+			case "test_bool":
+				ok = g.Get() == true
+			case "test_int":
+				ok = g.Get() == int(1)
+			case "test_int64":
+				ok = g.Get() == int64(2)
+			case "test_uint":
+				ok = g.Get() == uint(3)
+			case "test_uint64":
+				ok = g.Get() == uint64(4)
+			case "test_string":
+				ok = g.Get() == "5"
+			case "test_float64":
+				ok = g.Get() == float64(6)
+			case "test_duration":
+				ok = g.Get() == time.Duration(7)
+			}
+			if !ok {
+				t.Errorf("Visit: bad value %T(%v) for %s", g.Get(), g.Get(), f.Name)
+			}
+		}
+	}
+	VisitAll(visitor)
+}
+
 func TestUsage(t *testing.T) {
 	called := false
 	ResetForTesting(func() { called = true })