expvar: add Func for functions that return values that are JSON marshalable.

Remove {Float,Int,String}Func, which are now redundant.

Fixes #1684.

R=rsc, r, r2
CC=golang-dev
https://golang.org/cl/4410041

src/pkg/expvar/expvar.go

@@ -180,23 +180,14 @@ func (v *String) String() string { return strconv.Quote(v.s) }
 
 func (v *String) Set(value string) { v.s = value }
 
-// IntFunc wraps a func() int64 to create a value that satisfies the Var interface.
-// The function will be called each time the Var is evaluated.
-type IntFunc func() int64
+// Func implements Var by calling the function
+// and formatting the returned value using JSON.
+type Func func() interface{}
 
-func (v IntFunc) String() string { return strconv.Itoa64(v()) }
-
-// FloatFunc wraps a func() float64 to create a value that satisfies the Var interface.
-// The function will be called each time the Var is evaluated.
-type FloatFunc func() float64
-
-func (v FloatFunc) String() string { return strconv.Ftoa64(v(), 'g', -1) }
-
-// StringFunc wraps a func() string to create value that satisfies the Var interface.
-// The function will be called each time the Var is evaluated.
-type StringFunc func() string
-
-func (f StringFunc) String() string { return strconv.Quote(f()) }
+func (f Func) String() string {
+	v, _ := json.Marshal(f())
+	return string(v)
+}
 
 
 // All published variables.
@@ -282,18 +273,16 @@ func expvarHandler(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprintf(w, "\n}\n")
 }
 
-func memstats() string {
-	b, _ := json.MarshalIndent(&runtime.MemStats, "", "\t")
-	return string(b)
+func cmdline() interface{} {
+	return os.Args
 }
 
-func cmdline() string {
-	b, _ := json.Marshal(os.Args)
-	return string(b)
+func memstats() interface{} {
+	return runtime.MemStats
 }
 
 func init() {
 	http.Handle("/debug/vars", http.HandlerFunc(expvarHandler))
-	Publish("cmdline", StringFunc(cmdline))
-	Publish("memstats", StringFunc(memstats))
+	Publish("cmdline", Func(cmdline))
+	Publish("memstats", Func(memstats))
 }

src/pkg/expvar/expvar_test.go

@@ -114,41 +114,15 @@ func TestMapCounter(t *testing.T) {
 	}
 }
 
-func TestIntFunc(t *testing.T) {
-	x := int64(4)
-	ix := IntFunc(func() int64 { return x })
-	if s := ix.String(); s != "4" {
-		t.Errorf("ix.String() = %v, want 4", s)
+func TestFunc(t *testing.T) {
+	var x interface{} = []string{"a", "b"}
+	f := Func(func() interface{} { return x })
+	if s, exp := f.String(), `["a","b"]`; s != exp {
+		t.Errorf(`f.String() = %q, want %q`, s, exp)
 	}
 
-	x++
-	if s := ix.String(); s != "5" {
-		t.Errorf("ix.String() = %v, want 5", s)
-	}
-}
-
-func TestFloatFunc(t *testing.T) {
-	x := 8.5
-	ix := FloatFunc(func() float64 { return x })
-	if s := ix.String(); s != "8.5" {
-		t.Errorf("ix.String() = %v, want 3.14", s)
-	}
-
-	x -= 1.25
-	if s := ix.String(); s != "7.25" {
-		t.Errorf("ix.String() = %v, want 4.34", s)
-	}
-}
-
-func TestStringFunc(t *testing.T) {
-	x := "hello"
-	sx := StringFunc(func() string { return x })
-	if s, exp := sx.String(), `"hello"`; s != exp {
-		t.Errorf(`sx.String() = %q, want %q`, s, exp)
-	}
-
-	x = "goodbye"
-	if s, exp := sx.String(), `"goodbye"`; s != exp {
-		t.Errorf(`sx.String() = %q, want %q`, s, exp)
+	x = 17
+	if s, exp := f.String(), `17`; s != exp {
+		t.Errorf(`f.String() = %q, want %q`, s, exp)
 	}
 }