cp pointers util from kubernetes/kubernetes

README.md

@@ -45,6 +45,8 @@ an existing package to this repository.
 
 - [Clock](/clock) provides an interface for time-based operations.  It allows
   mocking time for testing.
+
+- [Pointers](/pointers) provides some functions for pointer-based operations.
 
 [Build Status]: https://travis-ci.org/kubernetes/utils.svg?branch=master
 [Go standard libs]: https://golang.org/pkg/#stdlib

pointer/pointer.go

@@ -0,0 +1,76 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package pointer
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// AllPtrFieldsNil tests whether all pointer fields in a struct are nil.  This is useful when,
+// for example, an API struct is handled by plugins which need to distinguish
+// "no plugin accepted this spec" from "this spec is empty".
+//
+// This function is only valid for structs and pointers to structs.  Any other
+// type will cause a panic.  Passing a typed nil pointer will return true.
+func AllPtrFieldsNil(obj interface{}) bool {
+	v := reflect.ValueOf(obj)
+	if !v.IsValid() {
+		panic(fmt.Sprintf("reflect.ValueOf() produced a non-valid Value for %#v", obj))
+	}
+	if v.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			return true
+		}
+		v = v.Elem()
+	}
+	for i := 0; i < v.NumField(); i++ {
+		if v.Field(i).Kind() == reflect.Ptr && !v.Field(i).IsNil() {
+			return false
+		}
+	}
+	return true
+}
+
+// Int32Ptr returns a pointer to an int32
+func Int32Ptr(i int32) *int32 {
+	return &i
+}
+
+// Int64Ptr returns a pointer to an int64
+func Int64Ptr(i int64) *int64 {
+	return &i
+}
+
+// Int32PtrDerefOr dereference the int32 ptr and returns it i not nil,
+// else returns def.
+func Int32PtrDerefOr(ptr *int32, def int32) int32 {
+	if ptr != nil {
+		return *ptr
+	}
+	return def
+}
+
+// BoolPtr returns a pointer to a bool
+func BoolPtr(b bool) *bool {
+	return &b
+}
+
+// StringPtr returns a pointer to the passed string.
+func StringPtr(s string) *string {
+	return &s
+}

pointer/pointer_test.go

@@ -0,0 +1,66 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package pointer
+
+import (
+	"testing"
+)
+
+func TestAllPtrFieldsNil(t *testing.T) {
+	testCases := []struct {
+		obj      interface{}
+		expected bool
+	}{
+		{struct{}{}, true},
+		{struct{ Foo int }{12345}, true},
+		{&struct{ Foo int }{12345}, true},
+		{struct{ Foo *int }{nil}, true},
+		{&struct{ Foo *int }{nil}, true},
+		{struct {
+			Foo int
+			Bar *int
+		}{12345, nil}, true},
+		{&struct {
+			Foo int
+			Bar *int
+		}{12345, nil}, true},
+		{struct {
+			Foo *int
+			Bar *int
+		}{nil, nil}, true},
+		{&struct {
+			Foo *int
+			Bar *int
+		}{nil, nil}, true},
+		{struct{ Foo *int }{new(int)}, false},
+		{&struct{ Foo *int }{new(int)}, false},
+		{struct {
+			Foo *int
+			Bar *int
+		}{nil, new(int)}, false},
+		{&struct {
+			Foo *int
+			Bar *int
+		}{nil, new(int)}, false},
+		{(*struct{})(nil), true},
+	}
+	for i, tc := range testCases {
+		if AllPtrFieldsNil(tc.obj) != tc.expected {
+			t.Errorf("case[%d]: expected %t, got %t", i, tc.expected, !tc.expected)
+		}
+	}
+}