Implement String method for pointers (#122)

* Implement String method for pointers

By implementing this method ourselves using atomic
loading and fmt.Sprint, we can avoid possible unguarded
accesses to the embedded pointer if someone attempts to
fmt.Print the atomic.Pointer
.

* Use Pointer.Load, not wrapped.Load

Co-authored-by: Abhinav Gupta <abg@uber.com>

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+### Added
+- Add `String` method to `atomic.Pointer[T]` type allowing users to safely print
+underlying values of pointers.
+
 ## [1.10.0] - 2022-08-11
 ### Added
 - Add `atomic.Float32` type for atomic operations on `float32`.

pointer_go118.go

@@ -18,43 +18,14 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
-//go:build go1.18 && !go1.19
-// +build go1.18,!go1.19
+//go:build go1.18
+// +build go1.18
 
 package atomic
 
-import "unsafe"
+import "fmt"
 
-type Pointer[T any] struct {
-	_ nocmp // disallow non-atomic comparison
-	p UnsafePointer
-}
-
-// NewPointer creates a new Pointer.
-func NewPointer[T any](v *T) *Pointer[T] {
-	var p Pointer[T]
-	if v != nil {
-		p.p.Store(unsafe.Pointer(v))
-	}
-	return &p
-}
-
-// Load atomically loads the wrapped value.
-func (p *Pointer[T]) Load() *T {
-	return (*T)(p.p.Load())
-}
-
-// Store atomically stores the passed value.
-func (p *Pointer[T]) Store(val *T) {
-	p.p.Store(unsafe.Pointer(val))
-}
-
-// Swap atomically swaps the wrapped pointer and returns the old value.
-func (p *Pointer[T]) Swap(val *T) (old *T) {
-	return (*T)(p.p.Swap(unsafe.Pointer(val)))
-}
-
-// CompareAndSwap is an atomic compare-and-swap.
-func (p *Pointer[T]) CompareAndSwap(old, new *T) (swapped bool) {
-	return p.p.CompareAndSwap(unsafe.Pointer(old), unsafe.Pointer(new))
+// String returns a human readable representation of a Pointer's underlying value.
+func (p *Pointer[T]) String() string {
+	return fmt.Sprint(p.Load())
 }

pointer_go118_pre119.go

@@ -0,0 +1,60 @@
+// Copyright (c) 2022 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+//go:build go1.18 && !go1.19
+// +build go1.18,!go1.19
+
+package atomic
+
+import "unsafe"
+
+type Pointer[T any] struct {
+	_ nocmp // disallow non-atomic comparison
+	p UnsafePointer
+}
+
+// NewPointer creates a new Pointer.
+func NewPointer[T any](v *T) *Pointer[T] {
+	var p Pointer[T]
+	if v != nil {
+		p.p.Store(unsafe.Pointer(v))
+	}
+	return &p
+}
+
+// Load atomically loads the wrapped value.
+func (p *Pointer[T]) Load() *T {
+	return (*T)(p.p.Load())
+}
+
+// Store atomically stores the passed value.
+func (p *Pointer[T]) Store(val *T) {
+	p.p.Store(unsafe.Pointer(val))
+}
+
+// Swap atomically swaps the wrapped pointer and returns the old value.
+func (p *Pointer[T]) Swap(val *T) (old *T) {
+	return (*T)(p.p.Swap(unsafe.Pointer(val)))
+}
+
+// CompareAndSwap is an atomic compare-and-swap.
+func (p *Pointer[T]) CompareAndSwap(old, new *T) (swapped bool) {
+	return p.p.CompareAndSwap(unsafe.Pointer(old), unsafe.Pointer(new))
+}

pointer_test.go

@@ -24,6 +24,7 @@
 package atomic
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -89,6 +90,10 @@ func TestPointer(t *testing.T) {
 				atom.Store(&i)
 				require.Equal(t, &i, atom.Load(), "Store didn't set the correct value.")
 			})
+			t.Run("String", func(t *testing.T) {
+				atom := tt.newAtomic()
+				require.Equal(t, fmt.Sprint(tt.initial), atom.String(), "String did not return the correct value.")
+			})
 		})
 	}
 }