type Callback func(context.Context, Observer) error

type Meter interface {
	// Int64Counter returns a new instrument identified by name and configured
	// with options. The instrument is used to synchronously record increasing
	// int64 measurements during a computational operation.
	Int64Counter(name string, options ...instrument.Int64CounterOption) (instrument.Int64Counter, error)
	// Int64UpDownCounter returns a new instrument identified by name and
	// configured with options. The instrument is used to synchronously record
	// int64 measurements during a computational operation.
	Int64UpDownCounter(name string, options ...instrument.Int64UpDownCounterOption) (instrument.Int64UpDownCounter, error)
	// Int64Histogram returns a new instrument identified by name and
	// configured with options. The instrument is used to synchronously record
	// the distribution of int64 measurements during a computational operation.
	Int64Histogram(name string, options ...instrument.Int64HistogramOption) (instrument.Int64Histogram, error)
	// Int64ObservableCounter returns a new instrument identified by name and
	// configured with options. The instrument is used to asynchronously record
	// increasing int64 measurements once per a measurement collection cycle.
	Int64ObservableCounter(name string, options ...instrument.Int64ObservableCounterOption) (instrument.Int64ObservableCounter, error)
	// Int64ObservableUpDownCounter returns a new instrument identified by name
	// and configured with options. The instrument is used to asynchronously
	// record int64 measurements once per a measurement collection cycle.
	Int64ObservableUpDownCounter(name string, options ...instrument.Int64ObservableUpDownCounterOption) (instrument.Int64ObservableUpDownCounter, error)
	// Int64ObservableGauge returns a new instrument identified by name and
	// configured with options. The instrument is used to asynchronously record
	// instantaneous int64 measurements once per a measurement collection
	// cycle.
	Int64ObservableGauge(name string, options ...instrument.Int64ObservableGaugeOption) (instrument.Int64ObservableGauge, error)

	// Float64Counter returns a new instrument identified by name and
	// configured with options. The instrument is used to synchronously record
	// increasing float64 measurements during a computational operation.
	Float64Counter(name string, options ...instrument.Float64CounterOption) (instrument.Float64Counter, error)
	// Float64UpDownCounter returns a new instrument identified by name and
	// configured with options. The instrument is used to synchronously record
	// float64 measurements during a computational operation.
	Float64UpDownCounter(name string, options ...instrument.Float64UpDownCounterOption) (instrument.Float64UpDownCounter, error)
	// Float64Histogram returns a new instrument identified by name and
	// configured with options. The instrument is used to synchronously record
	// the distribution of float64 measurements during a computational
	// operation.
	Float64Histogram(name string, options ...instrument.Float64HistogramOption) (instrument.Float64Histogram, error)
	// Float64ObservableCounter returns a new instrument identified by name and
	// configured with options. The instrument is used to asynchronously record
	// increasing float64 measurements once per a measurement collection cycle.
	Float64ObservableCounter(name string, options ...instrument.Float64ObservableCounterOption) (instrument.Float64ObservableCounter, error)
	// Float64ObservableUpDownCounter returns a new instrument identified by
	// name and configured with options. The instrument is used to
	// asynchronously record float64 measurements once per a measurement
	// collection cycle.
	Float64ObservableUpDownCounter(name string, options ...instrument.Float64ObservableUpDownCounterOption) (instrument.Float64ObservableUpDownCounter, error)
	// Float64ObservableGauge returns a new instrument identified by name and
	// configured with options. The instrument is used to asynchronously record
	// instantaneous float64 measurements once per a measurement collection
	// cycle.
	Float64ObservableGauge(name string, options ...instrument.Float64ObservableGaugeOption) (instrument.Float64ObservableGauge, error)

	// RegisterCallback registers f to be called during the collection of a
	// measurement cycle.
	//
	// If Unregister of the returned Registration is called, f needs to be
	// unregistered and not called during collection.
	//
	// The instruments f is registered with are the only instruments that f may
	// observe values for.
	//
	// If no instruments are passed, f should not be registered nor called
	// during collection.
	RegisterCallback(f Callback, instruments ...instrument.Observable) (Registration, error)
}

type MeterConfig struct {
	// contains filtered or unexported fields
}

type MeterOption interface {
	// contains filtered or unexported methods
}

type MeterProvider interface {
	// Meter returns a new Meter with the provided name and configuration.
	//
	// A Meter should be scoped at most to a single package. The name needs to
	// be unique so it does not collide with other names used by
	// an application, nor other applications. To achieve this, the import path
	// of the instrumentation package is recommended to be used as name.
	//
	// If the name is empty, then an implementation defined default name will
	// be used instead.
	Meter(name string, opts ...MeterOption) Meter
}

type Observer interface {
	// ObserveFloat64 records the float64 value with attributes for obsrv.
	ObserveFloat64(obsrv instrument.Float64Observable, value float64, attributes ...attribute.KeyValue)
	// ObserveInt64 records the int64 value with attributes for obsrv.
	ObserveInt64(obsrv instrument.Int64Observable, value int64, attributes ...attribute.KeyValue)
}

type Registration interface {
	// Unregister removes the callback registration from a Meter.
	//
	// This method needs to be idempotent and concurrent safe.
	Unregister() error
}