Remove comparable constraint on Readers.

sdk/metric/config.go

@@ -29,7 +29,7 @@ import (
 // config contains configuration options for a MeterProvider.
 type config struct {
 	res     *resource.Resource
-	readers map[Reader][]view.View
+	entries []registryEntry
 }
 
 // readerSignals returns a force-flush and shutdown function for a
@@ -38,9 +38,9 @@ type config struct {
 // single functions.
 func (c config) readerSignals() (forceFlush, shutdown func(context.Context) error) {
 	var fFuncs, sFuncs []func(context.Context) error
-	for r := range c.readers {
-		sFuncs = append(sFuncs, r.Shutdown)
-		fFuncs = append(fFuncs, r.ForceFlush)
+	for _, ent := range c.entries {
+		sFuncs = append(sFuncs, ent.reader.Shutdown)
+		fFuncs = append(fFuncs, ent.reader.ForceFlush)
 	}
 
 	return unify(fFuncs), unifyShutdown(sFuncs)
@@ -126,14 +126,14 @@ func WithResource(res *resource.Resource) Option {
 // operations; no data will be exported without a Reader.
 func WithReader(r Reader, views ...view.View) Option {
 	return optionFunc(func(cfg config) config {
-		if cfg.readers == nil {
-			cfg.readers = make(map[Reader][]view.View)
-		}
 		if len(views) == 0 {
 			views = []view.View{{}}
 		}
 
-		cfg.readers[r] = views
+		cfg.entries = append(cfg.entries, registryEntry{
+			reader: r,
+			views:  views,
+		})
 		return cfg
 	})
 }

sdk/metric/config_test.go

@@ -130,5 +130,5 @@ func TestWithResource(t *testing.T) {
 func TestWithReader(t *testing.T) {
 	r := &reader{}
 	c := newConfig([]Option{WithReader(r)})
-	assert.Contains(t, c.readers, r)
+	assert.Contains(t, c.entries, registryEntry{reader: r, views: []view.View{{}}})
 }

sdk/metric/pipeline.go

@@ -161,27 +161,34 @@ func (p *pipeline) produce(ctx context.Context) (metricdata.ResourceMetrics, err
 // pipelineRegistry manages creating pipelines, and aggregators.  Meters retrieve
 // new Aggregators from a pipelineRegistry.
 type pipelineRegistry struct {
-	views     map[Reader][]view.View
-	pipelines map[Reader]*pipeline
+	entries []registryEntry
 }
 
-func newPipelineRegistries(views map[Reader][]view.View) *pipelineRegistry {
-	pipelines := map[Reader]*pipeline{}
-	for rdr := range views {
-		pipe := &pipeline{}
-		rdr.register(pipe)
-		pipelines[rdr] = pipe
+type registryEntry struct {
+	reader   Reader
+	views    []view.View
+	pipeline *pipeline
+}
+
+func newPipelineRegistries(entries []registryEntry) *pipelineRegistry {
+	reg := &pipelineRegistry{
+		entries: make([]registryEntry, len(entries)),
 	}
-	return &pipelineRegistry{
-		views:     views,
-		pipelines: pipelines,
+	for i, entry := range entries {
+		entry.pipeline = &pipeline{}
+		entry.reader.register(entry.pipeline)
+		reg.entries[i] = entry
 	}
+	return reg
 }
 
 // TODO (#3053) Only register callbacks if any instrument matches in a view.
 func (reg *pipelineRegistry) registerCallback(fn func(context.Context)) {
-	for _, pipe := range reg.pipelines {
-		pipe.addCallback(fn)
+	// for _, pipe := range reg.pipelines {
+	// 	pipe.addCallback(fn)
+	// }
+	for _, entry := range reg.entries {
+		entry.pipeline.addCallback(fn)
 	}
 }
 
@@ -192,8 +199,10 @@ func createAggregators[N int64 | float64](reg *pipelineRegistry, inst view.Instr
 	var aggs []internal.Aggregator[N]
 
 	errs := &multierror{}
-	for rdr, views := range reg.views {
-		pipe := reg.pipelines[rdr]
+	for _, entry := range reg.entries {
+		rdr := entry.reader
+		views := entry.views
+		pipe := entry.pipeline
 		rdrAggs, err := createAggregatorsForReader[N](rdr, views, inst)
 		if err != nil {
 			errs.append(err)

sdk/metric/pipeline_registry_test.go

@@ -252,7 +252,7 @@ func TestPipelineRegistryCreateAggregators(t *testing.T) {
 
 	testCases := []struct {
 		name      string
-		views     map[Reader][]view.View
+		entries   []registryEntry
 		inst      view.Instrument
 		wantCount int
 	}{
@@ -263,59 +263,75 @@ func TestPipelineRegistryCreateAggregators(t *testing.T) {
 		{
 			name: "1 reader 1 view gets 1 aggregator",
 			inst: view.Instrument{Name: "foo"},
-			views: map[Reader][]view.View{
-				testRdr: {
-					{},
-				},
+			entries: []registryEntry{
+				{reader: testRdr, views: []view.View{{}}},
 			},
 			wantCount: 1,
 		},
 		{
 			name: "1 reader 2 views gets 2 aggregator",
 			inst: view.Instrument{Name: "foo"},
-			views: map[Reader][]view.View{
-				testRdr: {
-					{},
-					renameView,
+			entries: []registryEntry{
+				{
+					reader: testRdr,
+					views: []view.View{
+						{},
+						renameView,
+					},
 				},
 			},
 			wantCount: 2,
 		},
 		{
 			name: "2 readers 1 view each gets 2 aggregators",
 			inst: view.Instrument{Name: "foo"},
-			views: map[Reader][]view.View{
-				testRdr: {
-					{},
+			entries: []registryEntry{
+				{
+					reader: testRdr,
+					views: []view.View{
+						{},
+					},
 				},
-				testRdrHistogram: {
-					{},
+				{
+					reader: testRdrHistogram,
+					views: []view.View{
+						{},
+					},
 				},
 			},
 			wantCount: 2,
 		},
 		{
 			name: "2 reader 2 views each gets 4 aggregators",
 			inst: view.Instrument{Name: "foo"},
-			views: map[Reader][]view.View{
-				testRdr: {
-					{},
-					renameView,
+			entries: []registryEntry{
+				{
+					reader: testRdr,
+					views: []view.View{
+						{},
+						renameView,
+					},
 				},
-				testRdrHistogram: {
-					{},
-					renameView,
+				{
+					reader: testRdrHistogram,
+					views: []view.View{
+						{},
+						renameView,
+					},
 				},
 			},
 			wantCount: 4,
 		},
 		{
 			name: "An instrument is duplicated in two views share the same aggregator",
 			inst: view.Instrument{Name: "foo"},
-			views: map[Reader][]view.View{
-				testRdr: {
-					{},
-					{},
+			entries: []registryEntry{
+				{
+					reader: testRdr,
+					views: []view.View{
+						{},
+						{},
+					},
 				},
 			},
 			wantCount: 1,
@@ -324,9 +340,9 @@ func TestPipelineRegistryCreateAggregators(t *testing.T) {
 
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
-			reg := newPipelineRegistries(tt.views)
+			reg := newPipelineRegistries(tt.entries)
 			testPipelineRegistryCreateIntAggregators(t, reg, tt.wantCount)
-			reg = newPipelineRegistries(tt.views)
+			reg = newPipelineRegistries(tt.entries)
 			testPipelineRegistryCreateFloatAggregators(t, reg, tt.wantCount)
 		})
 	}
@@ -353,19 +369,17 @@ func testPipelineRegistryCreateFloatAggregators(t *testing.T, reg *pipelineRegis
 func TestPipelineRegistryCreateAggregatorsIncompatibleInstrument(t *testing.T) {
 	testRdrHistogram := NewManualReader(WithAggregationSelector(func(ik view.InstrumentKind) aggregation.Aggregation { return aggregation.ExplicitBucketHistogram{} }))
 
-	views := map[Reader][]view.View{
-		testRdrHistogram: {
-			{},
-		},
+	entries := []registryEntry{
+		{reader: testRdrHistogram, views: []view.View{{}}},
 	}
-	reg := newPipelineRegistries(views)
+	reg := newPipelineRegistries(entries)
 	inst := view.Instrument{Name: "foo", Kind: view.AsyncGauge}
 
 	intAggs, err := createAggregators[int64](reg, inst, unit.Dimensionless)
 	assert.Error(t, err)
 	assert.Len(t, intAggs, 0)
 
-	reg = newPipelineRegistries(views)
+	reg = newPipelineRegistries(entries)
 
 	floatAggs, err := createAggregators[float64](reg, inst, unit.Dimensionless)
 	assert.Error(t, err)
@@ -377,17 +391,21 @@ func TestPipelineRegistryCreateAggregatorsDuplicateErrors(t *testing.T) {
 		view.MatchInstrumentName("bar"),
 		view.WithRename("foo"),
 	)
-	views := map[Reader][]view.View{
-		NewManualReader(): {
-			{},
-			renameView,
+
+	entries := []registryEntry{
+		{
+			reader: NewManualReader(),
+			views: []view.View{
+				{},
+				renameView,
+			},
 		},
 	}
 
 	fooInst := view.Instrument{Name: "foo", Kind: view.SyncCounter}
 	barInst := view.Instrument{Name: "bar", Kind: view.SyncCounter}
 
-	reg := newPipelineRegistries(views)
+	reg := newPipelineRegistries(entries)
 
 	intAggs, err := createAggregators[int64](reg, fooInst, unit.Dimensionless)
 	assert.NoError(t, err)

sdk/metric/provider.go

@@ -51,7 +51,7 @@ func NewMeterProvider(options ...Option) *MeterProvider {
 
 	flush, sdown := conf.readerSignals()
 
-	registry := newPipelineRegistries(conf.readers)
+	registry := newPipelineRegistries(conf.entries)
 
 	return &MeterProvider{
 		res: conf.res,