flag: make zero FlagSet useful

This makes it possible to use a FlagSet as a
field in a larger struct.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5036041

diff --git a/src/pkg/flag/flag.go b/src/pkg/flag/flag.go
index 38b65d1a1eb0fa1ec0087f17b9007c01e05828d8..f13f7a45cd34fe60538159014ee597ae34165c6c 100644 (file)
--- a/src/pkg/flag/flag.go
+++ b/src/pkg/flag/flag.go
@@ -286,6 +286,9 @@ func (f *FlagSet) Set(name, value string) bool {
        if !ok {
                return false
        }
+       if f.actual == nil {
+               f.actual = make(map[string]*Flag)
+       }
        f.actual[name] = flag
        return true
 }
@@ -559,6 +562,9 @@ func (f *FlagSet) Var(value Value, name string, usage string) {
                fmt.Fprintf(os.Stderr, "%s flag redefined: %s\n", f.name, name)
                panic("flag redefinition") // Happens only if flags are declared with identical names
        }
+       if f.formal == nil {
+               f.formal = make(map[string]*Flag)
+       }
        f.formal[name] = flag
 }
 
@@ -586,6 +592,8 @@ func (f *FlagSet) failf(format string, a ...interface{}) os.Error {
 func (f *FlagSet) usage() {
        if f == commandLine {
                Usage()
+       } else if f.Usage == nil {
+               defaultUsage(f)
        } else {
                f.Usage()
        }
@@ -657,6 +665,9 @@ func (f *FlagSet) parseOne() (bool, os.Error) {
                        return false, f.failf("invalid value %q for flag: -%s", value, name)
                }
        }
+       if f.actual == nil {
+               f.actual = make(map[string]*Flag)
+       }
        f.actual[name] = flag
        return true, nil
 }
@@ -713,10 +724,15 @@ var commandLine = NewFlagSet(os.Args[0], ExitOnError)
 func NewFlagSet(name string, errorHandling ErrorHandling) *FlagSet {
        f := &FlagSet{
                name:          name,
-               actual:        make(map[string]*Flag),
-               formal:        make(map[string]*Flag),
                errorHandling: errorHandling,
        }
-       f.Usage = func() { defaultUsage(f) }
        return f
 }
+
+// Init sets the name and error handling property for a flag set.
+// By default, the zero FlagSet uses an empty name and the
+// ContinueOnError error handling policy.
+func (f *FlagSet) Init(name string, errorHandling ErrorHandling) {
+       f.name = name
+       f.errorHandling = errorHandling
+}

diff --git a/src/pkg/flag/flag_test.go b/src/pkg/flag/flag_test.go
index 19c0deaf5c98a824acc3308a85ab18c90b43a3cb..f13531669c1914dcd9ae9027c042ac01e4b76df2 100644 (file)
--- a/src/pkg/flag/flag_test.go
+++ b/src/pkg/flag/flag_test.go
@@ -180,7 +180,8 @@ func (f *flagVar) Set(value string) bool {
 }
 
 func TestUserDefined(t *testing.T) {
-       flags := NewFlagSet("test", ContinueOnError)
+       var flags FlagSet
+       flags.Init("test", ContinueOnError)
        var v flagVar
        flags.Var(&v, "v", "usage")
        if err := flags.Parse([]string{"-v", "1", "-v", "2", "-v=3"}); err != nil {