Added stream insertion operator.

api/Stream.h

@@ -128,6 +128,34 @@ class Stream : public Print
 
 #undef NO_IGNORE_CHAR
 
+template <class T>
+struct Format {  // Structure to store a value and a modifier.
+  T data;
+  int modifier;
+};
+
+template <class T>
+Format<T> format(T const data, int const modifier) {
+  Format<T> fmt {data, modifier};
+  return fmt;
+}
+
+
+template <class T>
+Stream& operator <<(Stream& stream, T const data) {  // Stream insertion operator for plain data types.
+  stream.print(data);
+  return stream;
+}
+
+template <class T>
+Stream& operator <<(Stream& stream, Format<T> const& parameters) {  // Stream insertion operator with modifiers (e.g., BIN, HEX, number of digits, etc.).
+  stream.print(parameters.data, parameters.modifier);
+  return stream;
+}
+
 }
 
-using arduino::Stream;
+using arduino::Stream;
+using arduino::Format;
+using arduino::format;
+using arduino::operator <<;

test/CMakeLists.txt

@@ -55,6 +55,7 @@ set(TEST_SRCS
   src/Stream/test_find.cpp
   src/Stream/test_findUntil.cpp
   src/Stream/test_getTimeout.cpp
+  src/Stream/test_insertion_operator.cpp
   src/Stream/test_parseFloat.cpp
   src/Stream/test_parseInt.cpp
   src/Stream/test_readBytes.cpp

test/src/Stream/test_insertion_operator.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2020 Arduino.  All rights reserved.
+ */
+
+/**************************************************************************************
+ * INCLUDE
+ **************************************************************************************/
+
+#include <catch.hpp>
+
+#include <MillisFake.h>
+#include <StreamMock.h>
+
+/**************************************************************************************
+ * TEST CODE
+ **************************************************************************************/
+
+TEST_CASE ("Testing 'Format' initialisation", "[Stream-insertion-operator-01]") {
+  Format<char> fmt {'a', 2};
+  REQUIRE(fmt.data == 'a');
+  REQUIRE(fmt.modifier == 2);
+}
+
+TEST_CASE ("Testing 'format' helper function", "[Stream-insertion-operator-02]") {
+  Format<char> fmt {format('a', 2)};
+  REQUIRE(fmt.data == 'a');
+  REQUIRE(fmt.modifier == 2);
+}
+
+TEST_CASE ("Testing basic insertion operator", "[Stream-insertion-operator-03]") {
+  StreamMock mock;
+  mock << 'a' << 12 << 'b' << 34;  // Note we cannot test C strings as `StreamMock` has its own << operator.
+  REQUIRE(mock.available() == 6);
+}
+
+TEST_CASE ("Testing insertion operator with modifiers", "[Stream-insertion-operator-03]") {
+  StreamMock mock;
+  mock << format(1.2, 4);   // Expands to `1.2000`.
+  REQUIRE(mock.available() == 6);
+  mock << format(12, BIN);  // Expands to `1100`.
+  REQUIRE(mock.available() == 10);
+}