code: func newpcpSingletonMetric(val interface{}, desc *pcpMetricDesc) (*pcpSingletonMetric, error) {
  	if !desc.t.IsCompatible(val) {
  		return nil, errors.Errorf("type %v is not compatible with value %v(%T)", desc.t, val, val)
  	}
  
  	val = desc.t.resolve(val)
  	return &pcpSingletonMetric{desc, val, nil}, nil
  }
docs: // newpcpSingletonMetric creates a new instance of pcpSingletonMetric.