Add k8s ptr

pkg/ptr/ptr.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2023 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 ptr
+
+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
+}
+
+// To returns a pointer to the given value.
+func To[T any](v T) *T {
+	return &v
+}
+
+// Deref dereferences ptr and returns the value it points to if no nil, or else
+// returns def.
+func Deref[T any](ptr *T, def T) T {
+	if ptr != nil {
+		return *ptr
+	}
+	return def
+}
+
+// Equal returns true if both arguments are nil or both arguments
+// dereference to the same value.
+func Equal[T comparable](a, b *T) bool {
+	if (a == nil) != (b == nil) {
+		return false
+	}
+	if a == nil {
+		return true
+	}
+	return *a == *b
+}