Remove comparability requirement for Readers

CHANGELOG.md

@@ -21,6 +21,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Slice attributes of `attribute` package are now comparable based on their value, not instance. (#3108 #3252)
 - Prometheus exporter will now cumulatively sum histogram buckets. (#3281)
+- Remove comparable requirement for `Reader`s. (#3290)
 - Export the sum of each histogram datapoint uniquely with the `go.opentelemetry.io/otel/exporters/otlpmetric` exporters. (#3284, #3293)
 
 ## [1.11.0/0.32.3] 2022-10-12

sdk/metric/config.go

@@ -26,7 +26,7 @@ import (
 // config contains configuration options for a MeterProvider.
 type config struct {
 	res     *resource.Resource
-	readers map[Reader][]view.View
+	viewers []viewer
 }
 
 // readerSignals returns a force-flush and shutdown function for a
@@ -35,9 +35,9 @@ 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 _, v := range c.viewers {
+		sFuncs = append(sFuncs, v.reader.Shutdown)
+		fFuncs = append(fFuncs, v.reader.ForceFlush)
 	}
 
 	return unify(fFuncs), unifyShutdown(sFuncs)
@@ -123,10 +123,7 @@ 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)
-		}
-		cfg.readers[r] = views
+		cfg.viewers = append(cfg.viewers, viewer{reader: r, views: views})
 		return cfg
 	})
 }

sdk/metric/config_test.go

@@ -127,5 +127,7 @@ func TestWithResource(t *testing.T) {
 func TestWithReader(t *testing.T) {
 	r := &reader{}
 	c := newConfig([]Option{WithReader(r)})
-	assert.Contains(t, c.readers, r)
+	require.Len(t, c.viewers, 1)
+	assert.Same(t, r, c.viewers[0].reader)
+	assert.Len(t, c.viewers[0].views, 0)
 }

sdk/metric/pipeline.go

@@ -51,14 +51,19 @@ type instrumentSync struct {
 	aggregator  aggregator
 }
 
-func newPipeline(res *resource.Resource, reader Reader, views []view.View) *pipeline {
+// viewer is a reader with the applicable views it will use when reading.
+type viewer struct {
+	reader Reader
+	views  []view.View
+}
+
+func newPipeline(res *resource.Resource, v viewer) *pipeline {
 	if res == nil {
 		res = resource.Empty()
 	}
 	return &pipeline{
 		resource:     res,
-		reader:       reader,
-		views:        views,
+		viewer:       v,
 		aggregations: make(map[instrumentation.Scope][]instrumentSync),
 	}
 }
@@ -69,10 +74,9 @@ func newPipeline(res *resource.Resource, reader Reader, views []view.View) *pipe
 // As instruments are created the instrument should be checked if it exists in the
 // views of a the Reader, and if so each aggregator should be added to the pipeline.
 type pipeline struct {
-	resource *resource.Resource
+	viewer
 
-	reader Reader
-	views  []view.View
+	resource *resource.Resource
 
 	sync.Mutex
 	aggregations map[instrumentation.Scope][]instrumentSync
@@ -401,15 +405,11 @@ func isAggregatorCompatible(kind view.InstrumentKind, agg aggregation.Aggregatio
 // measurement.
 type pipelines []*pipeline
 
-func newPipelines(res *resource.Resource, readers map[Reader][]view.View) pipelines {
-	pipes := make([]*pipeline, 0, len(readers))
-	for r, v := range readers {
-		p := &pipeline{
-			resource: res,
-			reader:   r,
-			views:    v,
-		}
-		r.register(p)
+func newPipelines(res *resource.Resource, viewers []viewer) pipelines {
+	pipes := make([]*pipeline, 0, len(viewers))
+	for _, v := range viewers {
+		p := newPipeline(res, v)
+		v.reader.register(p)
 		pipes = append(pipes, p)
 	}
 	return pipes