feat(iterator): add package to help work with new iter.Seq types (#358)

This package is meant to be used to adapt our existing iterators into type that can be consumed by Go's range expressions. See example for usage. Note this feature requires Go1.23+ and was tested with go1.23rc1.

v2/iterator/example_test.go

@@ -0,0 +1,75 @@
+// Copyright 2024, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+//go:build go1.23
+
+package iterator_test
+
+import (
+	"fmt"
+	"iter"
+
+	"github.com/googleapis/gax-go/v2/iterator"
+	otherit "google.golang.org/api/iterator"
+)
+
+type exampleType struct {
+	data []int
+	i    int
+}
+
+func (t *exampleType) next() (int, error) {
+	var v int
+	if t.i == len(t.data) {
+		return v, otherit.Done
+	}
+	v = t.data[t.i]
+	t.i++
+	return v, nil
+}
+
+func (t *exampleType) All() iter.Seq2[int, error] {
+	return iterator.RangeAdapter[int](t.next)
+}
+
+func ExampleRangeAdapter() {
+	t := &exampleType{
+		data: []int{1, 2, 3},
+	}
+	for v, err := range t.All() {
+		if err != nil {
+			// TODO: handle error
+		}
+		fmt.Println(v)
+	}
+	// Output:
+	// 1
+	// 2
+	// 3
+}

v2/iterator/iterator.go

@@ -0,0 +1,63 @@
+// Copyright 2024, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+//go:build go1.23
+
+// Package iterator contains helper for working with iterators. It is meant for
+// internal use only by the Go Client Libraries.
+package iterator
+
+import (
+	"iter"
+
+	otherit "google.golang.org/api/iterator"
+)
+
+// RangeAdapter transforms client iterator type into a [iter.Seq2] that can
+// be used with Go's range expressions.
+//
+// This is for internal use only.
+func RangeAdapter[T any](next func() (T, error)) iter.Seq2[T, error] {
+	var err error
+	return func(yield func(T, error) bool) {
+		for {
+			if err != nil {
+				return
+			}
+			var resp T
+			resp, err = next()
+			if err == otherit.Done {
+				return
+			}
+			if !yield(resp, err) {
+				return
+			}
+		}
+	}
+}