Add IsValidValue method to stats package.

buckets.go

@@ -16,7 +16,7 @@ func (b HistogramBuckets) Set(key string, buckets ...interface{}) {
 	v := make([]Value, len(buckets))
 
 	for i, b := range buckets {
-		v[i] = ValueOf(b)
+		v[i] = MustValueOf(ValueOf(b))
 	}
 
 	b[makeKey(key)] = v

field.go

@@ -10,7 +10,7 @@ type Field struct {
 
 // MakeField constructs and returns a new Field from name, value, and ftype.
 func MakeField(name string, value interface{}, ftype FieldType) Field {
-	f := Field{Name: name, Value: ValueOf(value)}
+	f := Field{Name: name, Value: MustValueOf(ValueOf(value))}
 	f.setType(ftype)
 	return f
 }

value.go

@@ -12,8 +12,17 @@ type Value struct {
 	bits uint64
 }
 
+func MustValueOf(v Value) Value {
+	if v.Type() == Invalid {
+		panic("stats.MustValueOf received a value of unsupported type")
+	}
+	return v
+}
+
 func ValueOf(v interface{}) Value {
 	switch x := v.(type) {
+	case Value:
+		return x
 	case nil:
 		return Value{}
 	case bool:
@@ -47,7 +56,7 @@ func ValueOf(v interface{}) Value {
 	case time.Duration:
 		return durationValue(x)
 	default:
-		panic("stats.ValueOf received a value of unsupported type")
+		return Value{typ: Invalid}
 	}
 }
 
@@ -182,6 +191,7 @@ const (
 	Uint
 	Float
 	Duration
+	Invalid
 )
 
 func (t Type) String() string {

value_test.go

@@ -5,8 +5,50 @@ import (
 	"reflect"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/require"
 )
 
+func TestMustValueOf(t *testing.T) {
+	tests := []struct {
+		name  string
+		in    interface{}
+		out   interface{}
+		panic bool
+	}{
+		{
+			name: "should not panic",
+			in:   42,
+			out:  ValueOf(42),
+		},
+		{
+			name:  "should panic",
+			in:    struct{}{},
+			panic: true,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if test.panic {
+				require.PanicsWithValue(t, "stats.MustValueOf received a value of unsupported type", func() {
+					MustValueOf(ValueOf(test.in))
+				})
+			} else {
+				out := MustValueOf(ValueOf(test.in))
+				require.EqualValues(t, test.out, out)
+			}
+		})
+	}
+}
+
+func TestValueOfIdentity(t *testing.T) {
+	v1 := ValueOf(3.14)
+	v2 := ValueOf(v1)
+	if !reflect.DeepEqual(v1, v2) {
+		t.Fatalf("Expected %+v to be equal to %+v", v2, v1)
+	}
+}
+
 func TestValueOf(t *testing.T) {
 	tests := []struct {
 		in  interface{}