test copyfrom; go work sync

go.mod

@@ -2,9 +2,13 @@ module github.com/lightstep/varopt
 
 go 1.21
 
+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/rogpeppe/go-internal v1.10.0 // indirect
-	github.com/stretchr/testify v1.8.4
+	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
 )

go.sum

@@ -1,5 +1,4 @@
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
-github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 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=
@@ -13,18 +12,12 @@ github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsK
 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/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
-github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
-github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
-github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
-github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
-github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+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/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 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

varopt.go

@@ -48,6 +48,8 @@ func New[T any](capacity int, rnd *rand.Rand) *Varopt[T] {
 	return v
 }
 
+// Init initializes a Varopt[T] in-place, avoiding an allocation
+// compared with New().
 func (v *Varopt[T]) Init(capacity int, rnd *rand.Rand) {
 	*v = Varopt[T]{
 		capacity: capacity,
@@ -68,6 +70,22 @@ func (s *Varopt[T]) Reset() {
 	s.totalWeight = 0
 }
 
+// CopyFrom copies the fields of `from` into this Varopt[T].
+func (s *Varopt[T]) CopyFrom(from *Varopt[T]) {
+	// Copy non-slice fields
+	cpy := *from
+	// Keep existing slices, reset
+	cpy.L = s.L[:0]
+	cpy.T = s.T[:0]
+	cpy.X = s.X[:0]
+	// Append to existing slices
+	cpy.L = append(cpy.L, from.L...)
+	cpy.T = append(cpy.T, from.T...)
+	cpy.X = append(cpy.X, from.X...)
+	// Assign back to `s`
+	*s = cpy
+}
+
 // Add considers a new observation for the sample with given weight.
 // If there is an item ejected from the sample as a result, the item
 // is returned to allow re-use of memory.

varopt_test.go

@@ -181,12 +181,35 @@ func TestReset(t *testing.T) {
 	require.Equal(t, sum, v.TotalWeight())
 	require.Less(t, 0., v.Tau())
 
+	var v2 varopt.Varopt[testInt]
+	v2.Init(capacity, rnd)
+	v2.CopyFrom(v)
+
+	var expect []testInt
+	for i := 0; i < v.Size(); i++ {
+		got, _ := v.Get(i)
+		expect = append(expect, got)
+	}
+
 	v.Reset()
 
 	require.Equal(t, 0, v.Size())
 	require.Equal(t, 0, v.TotalCount())
 	require.Equal(t, 0., v.TotalWeight())
 	require.Equal(t, 0., v.Tau())
+
+	require.Equal(t, capacity, v2.Size())
+	require.Equal(t, insert, v2.TotalCount())
+	require.Equal(t, sum, v2.TotalWeight())
+	require.Less(t, 0., v2.Tau())
+
+	var have []testInt
+	for i := 0; i < v2.Size(); i++ {
+		got, _ := v2.Get(i)
+		have = append(have, got)
+	}
+	require.Equal(t, expect, have)
+
 }
 
 func TestEject(t *testing.T) {