// KindBad indicates that the Value has no type and should not be used.
	KindBad ValueKind = iota

	// KindUint64 indicates that the type of the Value is a uint64.
	KindUint64

	// KindFloat64 indicates that the type of the Value is a float64.
	KindFloat64

	// KindFloat64Histogram indicates that the type of the Value is a *Float64Histogram.
	KindFloat64Histogram
)

// Value represents a metric value returned by the runtime.

	case KindString:
		s.appendString(v.str())
	case KindInt64:
		*s.buf = strconv.AppendInt(*s.buf, v.Int64(), 10)
	case KindUint64:
		*s.buf = strconv.AppendUint(*s.buf, v.Uint64(), 10)
	case KindFloat64:
		// json.Marshal is funny about floats; it doesn't
		// always match strconv.AppendFloat. So just call it.
		// That's expensive, but floats are rare.
		if err := appendJSONMarshal(s.buf, v.Float64()); err != nil {