[DRAFT] [pdata] Mutable/immutable pdata with interfaces

[dmitryax]

This is a PR alternative to #6798. The goal is the same: a compile-time solution to #6794.

Instead of introducing mutable structures with duplicated immutable methods, this PR utilizes interfaces to reduce the duplication by "embedding" non-mutable methods in the mutable interfaces.

The downside of this approach is that we have to bring back the aliasing for pcommon package since I don't see a way to expose an interface and have its implementation parts in the internal package.

The PR doesn't touch tests yet.

[bogdandrutu]

Why is this needed? I may miss something.

We still need an unexported func to disallow external implementations.

[dmitryax]

We still need an unexported func to disallow external implementations.

Why? I thought this should be able to play that role. Another reason for this is to simplify the access to the orig from interface instances passed as arguments, so instead of

func (es immutableSummaryDataPointSlice) CopyTo(dest MutableSummaryDataPointSlice) {
	destCap := cap(*dest.(mutableSummaryDataPointSlice).getOrig())

we have

func (es immutableSummaryDataPointSlice) CopyTo(dest MutableSummaryDataPointSlice) {
	destCap := cap(*dest.getOrig())

[bogdandrutu]

Alternative solution, with less code, no interfaces:

// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Code generated by "pdata/internal/cmd/pdatagen/main.go". DO NOT EDIT.
// To regenerate this file run "make genpdata".

package ptrace

import (
	"go.opentelemetry.io/collector/pdata/internal"
	"go.opentelemetry.io/collector/pdata/internal/data"
	otlptrace "go.opentelemetry.io/collector/pdata/internal/data/protogen/trace/v1"
	"go.opentelemetry.io/collector/pdata/pcommon"
)

// Span represents a single operation within a trace.
// See Span definition in OTLP: https://github.com/open-telemetry/opentelemetry-proto/blob/main/opentelemetry/proto/trace/v1/trace.proto
type Span struct {
	commonSpan
}

type MutableSpan struct {
	commonSpan
}

type commonSpan struct {
	orig *otlptrace.Span
}

func newSpan(orig *otlptrace.Span) Span {
	return Span{commonSpan: commonSpan{orig: orig}}
}

func newMutableSpan(orig *otlptrace.Span) MutableSpan {
	return MutableSpan{commonSpan: commonSpan{orig: orig}}
}

// NewSpan creates a new empty Span.
//
// This must be used only in testing code. Users should use "AppendEmpty" when part of a Slice,
// OR directly access the member if this is embedded in another struct.
func NewSpan() MutableSpan {
	return newMutableSpan(&otlptrace.Span{})
}

// MoveTo moves all properties from the current struct overriding the destination and
// resetting the current instance to its zero value
func (ms MutableSpan) MoveTo(dest MutableSpan) {
	*dest.orig = *ms.orig
	*ms.orig = otlptrace.Span{}
}

// TraceID returns the traceid associated with this Span.
func (ms commonSpan) TraceID() pcommon.TraceID {
	return pcommon.TraceID(ms.orig.TraceId)
}

// SetTraceID replaces the traceid associated with this Span.
func (ms MutableSpan) SetTraceID(v pcommon.TraceID) {
	ms.orig.TraceId = data.TraceID(v)
}

// SpanID returns the spanid associated with this Span.
func (ms commonSpan) SpanID() pcommon.SpanID {
	return pcommon.SpanID(ms.orig.SpanId)
}

// SetSpanID replaces the spanid associated with this Span.
func (ms MutableSpan) SetSpanID(v pcommon.SpanID) {
	ms.orig.SpanId = data.SpanID(v)
}

// TraceState returns the tracestate associated with this Span.
func (ms commonSpan) TraceState() pcommon.TraceState {
	return internal.NewImmutableTraceState(&ms.orig.TraceState)
}

// TraceState returns the tracestate associated with this Span.
func (ms MutableSpan) TraceState() pcommon.MutableTraceState {
	return internal.NewMutableTraceState(&ms.orig.TraceState)
}

// ParentSpanID returns the parentspanid associated with this Span.
func (ms commonSpan) ParentSpanID() pcommon.SpanID {
	return pcommon.SpanID(ms.orig.ParentSpanId)
}

// SetParentSpanID replaces the parentspanid associated with this Span.
func (ms MutableSpan) SetParentSpanID(v pcommon.SpanID) {
	ms.orig.ParentSpanId = data.SpanID(v)
}

// Name returns the name associated with this Span.
func (ms commonSpan) Name() string {
	return ms.orig.Name
}

// SetName replaces the name associated with this Span.
func (ms MutableSpan) SetName(v string) {
	ms.orig.Name = v
}

// Kind returns the kind associated with this Span.
func (ms commonSpan) Kind() SpanKind {
	return SpanKind(ms.orig.Kind)
}

// SetKind replaces the kind associated with this Span.
func (ms MutableSpan) SetKind(v SpanKind) {
	ms.orig.Kind = otlptrace.Span_SpanKind(v)
}

// StartTimestamp returns the starttimestamp associated with this Span.
func (ms commonSpan) StartTimestamp() pcommon.Timestamp {
	return pcommon.Timestamp(ms.orig.StartTimeUnixNano)
}

// SetStartTimestamp replaces the starttimestamp associated with this Span.
func (ms MutableSpan) SetStartTimestamp(v pcommon.Timestamp) {
	ms.orig.StartTimeUnixNano = uint64(v)
}

// EndTimestamp returns the endtimestamp associated with this Span.
func (ms commonSpan) EndTimestamp() pcommon.Timestamp {
	return pcommon.Timestamp(ms.orig.EndTimeUnixNano)
}

// SetEndTimestamp replaces the endtimestamp associated with this Span.
func (ms MutableSpan) SetEndTimestamp(v pcommon.Timestamp) {
	ms.orig.EndTimeUnixNano = uint64(v)
}

// Attributes returns the Attributes associated with this Span.
func (ms commonSpan) Attributes() pcommon.Map {
	return internal.NewImmutableMap(&ms.orig.Attributes)
}

func (ms MutableSpan) Attributes() pcommon.MutableMap {
	return internal.NewMutableMap(&ms.orig.Attributes)
}

// DroppedAttributesCount returns the droppedattributescount associated with this Span.
func (ms commonSpan) DroppedAttributesCount() uint32 {
	return ms.orig.DroppedAttributesCount
}

// SetDroppedAttributesCount replaces the droppedattributescount associated with this Span.
func (ms MutableSpan) SetDroppedAttributesCount(v uint32) {
	ms.orig.DroppedAttributesCount = v
}

// Events returns the Events associated with this Span.
func (ms commonSpan) Events() SpanEventSlice {
	return newImmutableSpanEventSlice(&ms.orig.Events)
}

func (ms MutableSpan) Events() MutableSpanEventSlice {
	return newMutableSpanEventSlice(&ms.orig.Events)
}

// DroppedEventsCount returns the droppedeventscount associated with this Span.
func (ms commonSpan) DroppedEventsCount() uint32 {
	return ms.orig.DroppedEventsCount
}

// SetDroppedEventsCount replaces the droppedeventscount associated with this Span.
func (ms MutableSpan) SetDroppedEventsCount(v uint32) {
	ms.orig.DroppedEventsCount = v
}

// Links returns the Links associated with this Span.
func (ms commonSpan) Links() SpanLinkSlice {
	return newImmutableSpanLinkSlice(&ms.orig.Links)
}

func (ms MutableSpan) Links() MutableSpanLinkSlice {
	return newMutableSpanLinkSlice(&ms.orig.Links)
}

// DroppedLinksCount returns the droppedlinkscount associated with this Span.
func (ms commonSpan) DroppedLinksCount() uint32 {
	return ms.orig.DroppedLinksCount
}

// SetDroppedLinksCount replaces the droppedlinkscount associated with this Span.
func (ms MutableSpan) SetDroppedLinksCount(v uint32) {
	ms.orig.DroppedLinksCount = v
}

// Status returns the status associated with this Span.
func (ms commonSpan) Status() Status {
	return newImmutableStatus(&ms.orig.Status)
}

// Status returns the status associated with this MutableSpan.
func (ms MutableSpan) Status() MutableStatus {
	return newMutableStatus(&ms.orig.Status)
}

// CopyTo copies all properties from the current struct overriding the destination.
func (ms commonSpan) CopyTo(dest MutableSpan) {
	dest.SetTraceID(ms.TraceID())
	dest.SetSpanID(ms.SpanID())
	ms.TraceState().CopyTo(dest.TraceState())
	dest.SetParentSpanID(ms.ParentSpanID())
	dest.SetName(ms.Name())
	dest.SetKind(ms.Kind())
	dest.SetStartTimestamp(ms.StartTimestamp())
	dest.SetEndTimestamp(ms.EndTimestamp())
	ms.Attributes().CopyTo(dest.Attributes())
	dest.SetDroppedAttributesCount(ms.DroppedAttributesCount())
	ms.Events().CopyTo(dest.Events())
	dest.SetDroppedEventsCount(ms.DroppedEventsCount())
	ms.Links().CopyTo(dest.Links())
	dest.SetDroppedLinksCount(ms.DroppedLinksCount())
	ms.Status().CopyTo(dest.Status())
}

[dmitryax]

Thanks! I was trying to avoid the common interface but it appeared to be required for most of the cases because of method name conflicts. So this approach should be less code indeed. I'll give it a try!

[dmitryax]

@bogdandrutu looks like MutableSpan and Span are still convertible between each other unless we add another private field to MutableSpan to prevent Span->MutableSpan conversion

[dmitryax]

I'd like to keep this PR for now, and submitted another draft instead #7140

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[dmitryax]

Closing in favor of #7140