`_TASK_STD_FUNCTION` should be for everyone.

[issuefiler]

The development environment

I’m working with Raspberry Pi Pico W’s on PlatformIO and my development environment is capable of building C++23 code. It has ARDUINO_ARCH_RP2040 defined and the __cplusplus expands to 202100L.

The problem

The documentation instructs to define _TASK_STD_FUNCTION in order to enable the support for std::function callbacks. However, defining it produces an error on my environment because of this microcontroller limitation.

TaskScheduler/src/TaskScheduler.h

Lines 285 to 290 in 4ccca1a

	#if !defined (ARDUINO_ARCH_ESP8266) && !defined (ARDUINO_ARCH_ESP32) && !defined (ARDUINO_ARCH_STM32)
	#ifdef _TASK_STD_FUNCTION
	#error Support for std::function only for ESP8266 or ESP32 architecture
	#undef _TASK_STD_FUNCTION
	#endif // _TASK_STD_FUNCTION
	#endif // ARDUINO_ARCH_ESP8266

Why std::function callbacks are needed

This is necessary to call non-static class methods.

Buzzer(const std::uint8_t pin_number) noexcept
	: pin_number{pin_number},
	task{
		TaskScheduler::immediate,
		TaskScheduler::forever,
		[this](void) -> void {this->play_the_next_note();},
		&(TaskScheduler::scheduler)
	} {
}

My suggestion

It’s all about std::function.

TaskScheduler/src/TaskSchedulerDeclarations.h

Lines 125 to 134 in 4ccca1a

	#ifdef _TASK_STD_FUNCTION
	#include <functional>
	typedef std::function<void()> TaskCallback;
	typedef std::function<void()> TaskOnDisable;
	typedef std::function<bool()> TaskOnEnable;
	#else
	typedef void (*TaskCallback)();
	typedef void (*TaskOnDisable)();
	typedef bool (*TaskOnEnable)();
	#endif // _TASK_STD_FUNCTION

It might be more prudent to use the __cplusplus and __has_cpp_attribute for the C++ feature detection, instead of endlessly expanding the whitelist for future devices.

My temporary solution

The code works flawlessly with #define ARDUINO_ARCH_STM32.

// TaskScheduler.cpp
// Written on January 28, February 12, 24, March 2, 4, 7, 9–11, and 16, 2024.
////////////////////////////////////// 80 //////////////////////////////////////

module;

#define _TASK_SLEEP_ON_IDLE_RUN
#define _TASK_STD_FUNCTION
	// Enable the support for “std::function” callbacks.
#define ARDUINO_ARCH_STM32 // Disguising as an STM32 microcontroller
	// to suppress the “Support for std::function
	// only for ESP8266 or ESP32 architecture” error.
#include <TaskScheduler.h> // Task, Scheduler, TASK_IMMEDIATE, TASK_FOREVER.
#undef ARDUINO_ARCH_STM32

export module TaskScheduler;

export namespace TaskScheduler {
	inline constexpr unsigned long int immediate{TASK_IMMEDIATE};
	inline constexpr long int forever{TASK_FOREVER};

	using Task = ::Task;

	::Scheduler scheduler;

	inline bool execute(void) {
		// “true” if it has called a task callback.
		return !(TaskScheduler::scheduler.execute());
	}
};