PlaceholderInit added

examples/arduino/DallasTemperature/DallasTemperature.ino

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2022,2024 Piotr Stolarz
+ * Copyright (c) 2019-2022,2024,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -164,11 +164,10 @@ void loop()
     /* single sensor environment */
 
     /*
-     * Scratchpad placeholder is static to allow reuse of the associated
-     * sensor id while reissuing readScratchpadSingle() calls.
-     * Note, due to its storage class the placeholder is zero initialized.
+     * Zero-initialized scratchpad placeholder is static to allow reuse of
+     * the associated sensor id while reissuing readScratchpadSingle() calls.
      */
-    static Placeholder<DSTherm::Scratchpad> scrpd;
+    static PlaceholderInit<DSTherm::Scratchpad> scrpd;
 
     OneWireNg::ErrorCode ec = drv.readScratchpadSingle(scrpd);
     if (ec == OneWireNg::EC_SUCCESS) {

examples/esp-idf/DallasTemperature/main/DallasTemperature.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022,2024 Piotr Stolarz
+ * Copyright (c) 2022,2024,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -128,11 +128,10 @@ void loop()
     /* single sensor environment */
 
     /*
-     * Scratchpad placeholder is static to allow reuse of the associated
-     * sensor id while reissuing readScratchpadSingle() calls.
-     * Note, due to its storage class the placeholder is zero initialized.
+     * Zero-initialized scratchpad placeholder is static to allow reuse of
+     * the associated sensor id while reissuing readScratchpadSingle() calls.
      */
-    static Placeholder<DSTherm::Scratchpad> scrpd;
+    static PlaceholderInit<DSTherm::Scratchpad> scrpd;
 
     OneWireNg::ErrorCode ec = drv.readScratchpadSingle(scrpd);
     if (ec == OneWireNg::EC_SUCCESS) {

examples/mbed-os/DallasTemperature/DallasTemperature.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022,2024 Piotr Stolarz
+ * Copyright (c) 2022,2024,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -134,11 +134,10 @@ void loop()
     /* single sensor environment */
 
     /*
-     * Scratchpad placeholder is static to allow reuse of the associated
-     * sensor id while reissuing readScratchpadSingle() calls.
-     * Note, due to its storage class the placeholder is zero initialized.
+     * Zero-initialized scratchpad placeholder is static to allow reuse of
+     * the associated sensor id while reissuing readScratchpadSingle() calls.
      */
-    static Placeholder<DSTherm::Scratchpad> scrpd;
+    static PlaceholderInit<DSTherm::Scratchpad> scrpd;
 
     OneWireNg::ErrorCode ec = drv.readScratchpadSingle(scrpd);
     if (ec == OneWireNg::EC_SUCCESS) {

examples/pico-sdk/DallasTemperature/DallasTemperature.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022,2024 Piotr Stolarz
+ * Copyright (c) 2022,2024,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -160,11 +160,10 @@ void loop()
     /* single sensor environment */
 
     /*
-     * Scratchpad placeholder is static to allow reuse of the associated
-     * sensor id while reissuing readScratchpadSingle() calls.
-     * Note, due to its storage class the placeholder is zero initialized.
+     * Zero-initialized scratchpad placeholder is static to allow reuse of
+     * the associated sensor id while reissuing readScratchpadSingle() calls.
      */
-    static Placeholder<DSTherm::Scratchpad> scrpd;
+    static PlaceholderInit<DSTherm::Scratchpad> scrpd;
 
     OneWireNg::ErrorCode ec = drv.readScratchpadSingle(scrpd);
     if (ec == OneWireNg::EC_SUCCESS) {

keywords.txt

@@ -22,6 +22,7 @@ OneWireNg_CurrentPlatform	KEYWORD1
 DSTherm	KEYWORD1
 MAX31850	KEYWORD1
 Placeholder	KEYWORD1
+PlaceholderInit	KEYWORD1
 
 Id	KEYWORD3
 ErrorCode	KEYWORD3

src/drivers/DSTherm.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021,2022,2024 Piotr Stolarz
+ * Copyright (c) 2021,2022,2024,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -369,8 +369,7 @@ class DSTherm
      *   is used and the @c readSingleId() is not called. To avoid ambiguous
      *   behavior of initial call of the routine resulted from using uninitialized
      *   memory of the scratchpad placeholder, it's recommended to initialize
-     *   the placeholder with zeroes. See @c Init parameter of @ref Placeholder
-     *   template.
+     *   the placeholder with zeroes. @see PlaceholderInit.
      * - If @c reuseId is @c false, the routine calls @c readSingleId() every
      *   time to scan the bus for a connected sensor.
      *

src/utils/Placeholder.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021,2022 Piotr Stolarz
+ * Copyright (c) 2021,2022,2025 Piotr Stolarz
  * OneWireNg: Arduino 1-wire service library
  *
  * Distributed under the 2-clause BSD License (the License)
@@ -12,19 +12,21 @@
 
 #ifndef __OWNG_PLACEHOLDER__
 #define __OWNG_PLACEHOLDER__
-
-#include <stdint.h>
-#include <string.h>  /* memset */
-#include "platform/Platform_New.h"
-
 /**
  * Simple placeholder template with automatic conversion to a reference or a
  * pointer of the stored object. Overloaded @c operator&() and @c operator*()
  * allow to retrieve casted address and a reference to the stored object.
  * @c operator->() enables accessing placeholded object's members.
  */
-template<class T, bool Init = false>
-class Placeholder
+
+#include <stdint.h>
+#include <string.h>  /* memset */
+#include "platform/Platform_New.h"
+
+namespace {
+
+template<class T, uint8_t B = 0, bool Init = false>
+class Placeholder_priv
 {
 public:
     T *operator&() {
@@ -51,16 +53,27 @@ class Placeholder
     ALLOC_ALIGNED uint8_t _buf[sizeof(T)];
 };
 
-/**
- * Zero initialized @c Placeholder specialization.
- */
-template<class T>
-class Placeholder<T, true>: public Placeholder<T, false>
+template<class T, uint8_t B>
+class Placeholder_priv<T, B, true>: public Placeholder_priv<T, B, false>
 {
 public:
-    Placeholder() {
-        memset(this->_buf, 0, sizeof(this->_buf));
+    Placeholder_priv() {
+        memset(this->_buf, B, sizeof(this->_buf));
     }
 };
 
+} /* namespace */
+
+/**
+ * Uninitialized placeholder - placeholder's memory not initialized.
+ */
+template<class T>
+struct Placeholder: Placeholder_priv<T> {};
+
+/**
+ * Initialized placeholder - placeholder's memory filled by @c B (0 by default).
+ */
+template<class T, uint8_t B = 0>
+struct PlaceholderInit: Placeholder_priv<T, B, true> {};
+
 #endif /* __OWNG_PLACEHOLDER__ */