Add generic support; CopyFrom() and Init() methods (#20)

This code was last updated before Go generics. It's an obvious win here,
and was easy to do.
Also adds CopyFrom() and Init() method in support of
lightstep/otel-launcher-go#576 and new tests.

Author: jmacd

Diff for: .circleci/config.yml

@@ -0,0 +1,20 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior. Include code samples here when possible.
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Additional context**
+Add any other context about the problem here.

Diff for: .github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,20 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

Diff for: .github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,9 @@
+**Description:** <Describe what has changed. 
+Ex. Fixing a bug - Describe the bug and how this fixes the issue.
+Ex. Adding a feature - Explain what this achieves.>
+
+**Link to tracking Issue:** <Issue number if applicable>
+
+**Testing:** < Describe what testing was performed and which tests were added.>
+
+**Documentation:** < Describe the documentation added.>

Diff for: .github/pull_request_template.md

@@ -0,0 +1,32 @@
+name: build
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+
+  build:
+    strategy:
+      matrix:
+        go-version: [1.21.3]
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Set up Go 1.x
+      uses: actions/setup-go@v2
+      with:
+        go-version: ${{ matrix.go-version }}
+      id: go
+
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v2
+
+    - name: Build
+      run: go test -v ./...
+
+    - name: Code coverage
+      run: bash <(curl -s https://codecov.io/bash)

Diff for: .github/workflows/build.yml

@@ -55,4 +55,4 @@ VarOpt supports merging independently collected samples one
 observation at a time.  This is useful for building distributed
 sampling schemes.  In this use-case, each node in a distributed system
 computes a weighted sample.  To combine samples, simply input all the
-observations and their corresponding weights into a new VarOpt sample.
+observations and their corresponding weights into a new VarOpt sample.

Diff for: README.md

@@ -56,17 +56,19 @@ func BenchmarkAdd_Exp_1000000(b *testing.B) {
 	benchmarkAdd(b, 1000000, expValue)
 }
 
+type thing struct{}
+
 func benchmarkAdd(b *testing.B, size int, f func(rnd *rand.Rand) float64) {
 	b.ReportAllocs()
 	rnd := rand.New(rand.NewSource(3331))
-	v := varopt.New(size, rnd)
+	v := varopt.New[thing](size, rnd)
 	weights := make([]float64, b.N)
 	for i := 0; i < b.N; i++ {
 		weights[i] = f(rnd)
 	}
 
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		v.Add(nil, weights[i])
+		v.Add(thing{}, weights[i])
 	}
 }

Diff for: benchmark_test.go

@@ -16,7 +16,7 @@ type curve struct {
 	stddev float64
 }
 
-type point struct {
+type testPoint struct {
 	color  int
 	xvalue float64
 }
@@ -47,7 +47,7 @@ func ExampleVaropt_GetOriginalWeight() {
 
 	// Construct a timeseries consisting of three colored signals,
 	// for x=0 to x=60 seconds.
-	var points []point
+	var points []testPoint
 
 	// origCounts stores the original signals at second granularity.
 	origCounts := make([][]int, len(colors))
@@ -66,7 +66,7 @@ func ExampleVaropt_GetOriginalWeight() {
 			continue
 		}
 		origCounts[choose][int(math.Floor(xvalue))]++
-		points = append(points, point{
+		points = append(points, testPoint{
 			color:  choose,
 			xvalue: xvalue,
 		})
@@ -83,7 +83,7 @@ func ExampleVaropt_GetOriginalWeight() {
 	// weight.  This ensures a uniform distribution of points in each
 	// second.
 	sampleSize := int(sampleRatio * float64(totalCount))
-	sampler := varopt.New(sampleSize, rnd)
+	sampler := varopt.New[testPoint](sampleSize, rnd)
 	for _, point := range points {
 		second := int(math.Floor(point.xvalue))
 		prob := float64(xcount[second]) / float64(totalCount)
@@ -103,9 +103,8 @@ func ExampleVaropt_GetOriginalWeight() {
 	// The effective count of each sample point is its output
 	// weight divided by its original weight.
 	for i := 0; i < sampler.Size(); i++ {
-		sample, weight := sampler.Get(i)
+		point, weight := sampler.Get(i)
 		origWeight := sampler.GetOriginalWeight(i)
-		point := sample.(point)
 		second := int(math.Floor(point.xvalue))
 		sampleCounts[point.color][second] += (weight / origWeight)
 		pointCounts[second]++

Diff for: frequency_test.go

@@ -1,5 +1,14 @@
 module github.com/lightstep/varopt
 
-go 1.15
+go 1.21
 
-require github.com/stretchr/testify v1.4.0
+require github.com/stretchr/testify v1.8.4
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/kr/pretty v0.3.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/rogpeppe/go-internal v1.11.0 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

Diff for: go.mod

@@ -1,11 +1,23 @@
-github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
-github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
-github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
+github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
+github.com/rogpeppe/go-internal v1.11.0/go.mod h1:ddIwULY96R17DhadqLgMfk9H9tvdUzkipdSkR5nkCZA=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
-gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

Diff for: go.sum

@@ -2,14 +2,14 @@
 
 package internal
 
-type Vsample struct {
-	Sample interface{}
+type Vsample[T any] struct {
+	Sample T
 	Weight float64
 }
 
-type SampleHeap []Vsample
+type SampleHeap[T any] []Vsample[T]
 
-func (sh *SampleHeap) Push(v Vsample) {
+func (sh *SampleHeap[T]) Push(v Vsample[T]) {
 	l := append(*sh, v)
 	n := len(l) - 1
 
@@ -27,7 +27,7 @@ func (sh *SampleHeap) Push(v Vsample) {
 	*sh = l
 }
 
-func (sh *SampleHeap) Pop() Vsample {
+func (sh *SampleHeap[T]) Pop() Vsample[T] {
 	l := *sh
 	n := len(l) - 1
 	result := l[0]

Diff for: internal/sampleheap.go

@@ -38,17 +38,20 @@ func (s *simpleHeap) Pop() interface{} {
 }
 
 func TestLargeHeap(t *testing.T) {
-	var L internal.SampleHeap
+	var L internal.SampleHeap[float64]
 	var S simpleHeap
 
 	for i := 0; i < 1e6; i++ {
 		v := rand.NormFloat64()
-		L.Push(internal.Vsample{Weight: v})
+		L.Push(internal.Vsample[float64]{
+			Sample: v,
+			Weight: v,
+		})
 		heap.Push(&S, v)
 	}
 
 	for len(S) > 0 {
-		v1 := heap.Pop(&S).(float64)
+		v1 := heap.Pop(&S)
 		v2 := L.Pop().Weight
 
 		require.Equal(t, v1, v2)

Diff for: internal/sampleheap_test.go

@@ -4,62 +4,63 @@ package simple
 
 import (
 	"math/rand"
-
-	"github.com/lightstep/varopt"
 )
 
 // Simple implements unweighted reservoir sampling using Algorithm R
 // from "Random sampling with a reservoir" by Jeffrey Vitter (1985)
 // https://en.wikipedia.org/wiki/Reservoir_sampling#Algorithm_R
-type Simple struct {
+type Simple[T any] struct {
 	capacity int
 	observed int
-	buffer   []varopt.Sample
+	buffer   []T
 	rnd      *rand.Rand
 }
 
 // New returns a simple reservoir sampler with given capacity
 // (i.e., reservoir size) and random number generator.
-func New(capacity int, rnd *rand.Rand) *Simple {
-	return &Simple{
+func New[T any](capacity int, rnd *rand.Rand) *Simple[T] {
+	s := &Simple[T]{}
+	s.Init(capacity, rnd)
+	return s
+}
+
+func (s *Simple[T]) Init(capacity int, rnd *rand.Rand) {
+	*s = Simple[T]{
 		capacity: capacity,
+		buffer:   make([]T, 0, s.capacity),
 		rnd:      rnd,
 	}
 }
 
 // Add considers a new observation for the sample.  Items have unit
 // weight.
-func (s *Simple) Add(span varopt.Sample) {
+func (s *Simple[T]) Add(item T) {
 	s.observed++
 
-	if s.buffer == nil {
-		s.buffer = make([]varopt.Sample, 0, s.capacity)
-	}
-
 	if len(s.buffer) < s.capacity {
-		s.buffer = append(s.buffer, span)
+		s.buffer = append(s.buffer, item)
 		return
 	}
 
 	// Give this a capacity/observed chance of replacing an existing entry.
 	index := s.rnd.Intn(s.observed)
 	if index < s.capacity {
-		s.buffer[index] = span
+		s.buffer[index] = item
 	}
 }
 
 // Get returns the i'th selected item from the sample.
-func (s *Simple) Get(i int) varopt.Sample {
+func (s *Simple[T]) Get(i int) T {
 	return s.buffer[i]
 }
 
 // Size returns the number of items in the sample.  If the reservoir is
 // full, Size() equals Capacity().
-func (s *Simple) Size() int {
+func (s *Simple[T]) Size() int {
 	return len(s.buffer)
 }
 
 // Count returns the number of items that were observed.
-func (s *Simple) Count() int {
+func (s *Simple[T]) Count() int {
 	return s.observed
 }

Diff for: simple/simple.go

@@ -10,8 +10,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-type iRec int
-
 func TestSimple(t *testing.T) {
 	const (
 		popSize        = 1e6
@@ -22,19 +20,19 @@ func TestSimple(t *testing.T) {
 
 	rnd := rand.New(rand.NewSource(17167))
 
-	ss := simple.New(sampleSize, rnd)
+	ss := simple.New[int](sampleSize, rnd)
 
 	psum := 0.
 	for i := 0; i < popSize; i++ {
-		ss.Add(iRec(i))
+		ss.Add(i)
 		psum += float64(i)
 	}
 
 	require.Equal(t, ss.Size(), sampleSize)
 
 	ssum := 0.0
 	for i := 0; i < sampleSize; i++ {
-		ssum += float64(ss.Get(i).(iRec))
+		ssum += float64(ss.Get(i))
 	}
 
 	require.InEpsilon(t, ssum/float64(ss.Size()), psum/popSize, epsilon)