etl/docs/callbacks/function.md

title
function

{{< callout type="warning">}} Deprecated: Please use the more versatile etl::delegate or etl::inplace_function classes instead. {{< /callout >}}

{{< callout type="info">}} Header: function.h
Since: TBC
{{< /callout >}}

A set of wrapper templates to allow a member or static function to be called without the caller having to know the specific details of the callee apart from the parameter type. The templates allow the called function to be abstracted.

This may be used to implement a platform abstraction layer that allows an embedded application to interface with multiple hardware platforms.

Template	Description
etl::function	Callbacks to free or member functions taking zero or one parameter. Function pointer at runtime.
etl::function_fv	Callback to a free function taking no parameters. (Functiion Void). Function pointer at compile time.
etl::function_fp	Callback to a free function taking one parameter. (Function Parameter). Function pointer at compile time.
etl::function_mv	Callback to a member function taking no parameters. (Member Void). Function pointer at compile time.
etl::function_imv	Callback to a member function taking no parameters. (Instance Member Void ). Instance reference and function pointer at compile time.
etl::function_mp	Callback to a member function taking one parameter. (Member Parameter). Function pointer at compile time.
etl::function_imp	Callback to a member function taking one parameter. (Instance Member Parameter). Instance reference and function pointer at compile time.

Instances of any of these types may be passed as pointers or references to etl::ifunction.

Interface classes.

template <typename TParameter>
class ifunction

Description
Interface class for a function taking one parameter.

---

template <>
class ifunction<void>

Description
Interface class for a function taking no parameters.

All of the following classes are derived from the above interface classes.

Function address at run time.

The functions are called indirectly through an internal pointer.

template <typename TObject, 
          typename TParameter>
class function : public ifunction<TParameter>

Description
Class for a member function taking one parameter.

---

template <typename TObject>
class function<TObject, void> : public ifunction<void>

Description
Class for a member function taking no parameters.

template <typename TParameter>
class function<void, TParameter> : public ifunction<TParameter>

Description
Class for a free function taking one parameter.

---

template <>
class function<void, void> : public ifunction<void>

Description
Class for a free function taking no parameters.

Function address at compile time.

These will be more efficient than the previous definitions, as the one level of indirection is eliminated.

template <typename TObject, 
          void (TObject::*Function)()>
class function_mv : public ifunction<void>

Description
Class for a member function taking no parameters.

---

template <typename TObject, 
          TObject& Instance, 
          void (TObject::*Function)()>
class function_imv : public ifunction<void>

Description
Class for a member function taking no parameters.

---

template <typename TObject, 
          typename TParameter, 
          void (TObject::*Function)(TParameter)>
class function_mp : public ifunction<TParameter>

Description
Class for a member function taking one parameter.

---

template <typename TObject, 
          typename TParameter, 
          TObject& Instance, 
          void (TObject::*Function)(TParameter)>
class function_imp : public ifunction<TParameter>

Description
Class for a member function taking one parameter.

---

template <void (*Function)()>
class function_fv : public ifunction<void>

Description
Class for a free function taking no parameters.

---

template <typename TParameter, 
          void (*Function)()>
class function_fp : public ifunction<TParameter>

Description
Class for a free function taking one parameter.

Example

etl::function

These templates are designed to enable easy creation of callbacks to global, static and class member functions without the caller having to know which type actually it is.

One use that is applicable to embedded platforms is to use them connect interrupt vectors to class member handling functions. Particularly useful when the code is applicable to multiple targets devices.

The template is designed in such a way that the caller does not need to be aware of the type of the callee.

The caller declares an instance of etl::function or one of its variants. The caller defines a pointer or reference to an etl::ifunction. This pointer or reference will be initialised with the instance defined in the caller.

Example

The interrupt vector table contains entries for three timer timeouts and two uart character rx handlers. These are vectored to normal static functions.

void Timer1TimeoutInterrupt();
void Timer2TimeoutInterrupt();
void Timer3TimeoutInterrupt();
void Uart1RxInterrupt();
void Uart2RxInterrupt();

The timer timeout interrupts are handled by an instance of the class Timer and the free function FreeTimerInterruptHandler. The UART Rx interrupts are handled by instances of the class Uart.

Timer1 interrupts call the member function of an instance of Timer. Timer2 interrupts call the static member function of Timer. Timer3 interrupts call the free function FreeTimerInterruptHandler. UART1 interrupts call the member function of instance 1 of Uart. UART1 interrupts call the member function of instance 2 of Uart.

#include <iostream>
#include <iomanip>

#include "function.h"

//********************************
// Fake UART Rx register.
//********************************
char get_char()
{
  static char c = 'A';
  return c++;
}

//********************************
// Interrupt vectors & callbacks. 
//********************************
// Callback interfaces.
// Note that they do not require any knowledge about the callee apart from the parameter type.
etl::ifunction<void>* timer1_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<void>* timer2_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<void>* timer3_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<char>* uart1_rx_callback; // A pointer to a callback taking a char parameter.
etl::ifunction<char>* uart2_rx_callback; // A pointer to a callback taking a char parameter.

extern "C"
{
// Function called from the timer1 interrupt vector.
void Timer1Interrupt()
{
  (*timer1_callback)();
}

// Function called from the timer2 interrupt vector.
void Timer2Interrupt()
{
  (*timer2_callback)();
}

// Function called from the timer3 interrupt vector.
void Timer3Interrupt()
{
  (*timer3_callback)();
}

// Function called from the UART1 rx interrupt vector.
void Uart1RxInterrupt()
{
  (*uart1_rx_callback)(get_char());
}

// Function called from the UART2 rx interrupt vector.
void Uart2RxInterrupt()
{
  (*uart2_rx_callback)(get_char());
}
}

//********************************
// Timer driver.
//********************************
class Timer
{
public:

  // Constructor.
  Timer()
  {
  }

  // Handler for interrupts from the timer.
  void MemberTimerInterruptHandler()
  {
    std::cout << "Timer interrupt (member)\n";
  }

  // Static handler for interrupts from the timer.
  static void StaticTimerInterruptHandler()
  {
    std::cout << "Timer interrupt (static)\n";
  }
};

//********************************
// Free function timer driver.
//********************************
void FreeTimerInterruptHandler()
{
  std::cout << "Timer interrupt (free)\n";
}

etl::function_fv<FreeTimerInterruptHandler> free_callback;

//********************************
// UART driver.
//********************************
class Uart
{
public:

  // Constructor.
  Uart(int port_id)
    : port_id(port_id)
  {
  }

  // Handler for rx interrupts from the UART.
  void RxInterruptHandler(char c)
  {
    std::cout << "UART" << port_id << " Rx char interrupt : Received '" << c << "'\n";
  }

  int port_id;
};

// Declare the driver instances.
Timer timer;
Uart  uart1(0);
Uart  uart2(1);

etl::function_imv<Timer, timer, &Timer::MemberTimerInterruptHandler> timer_member_callback;
etl::function_fv<&Timer::StaticTimerInterruptHandler>                timer_static_callback;
etl::function_imp<Uart, char, uart1, &Uart::RxInterruptHandler>      uart1_callback;
etl::function_imp<Uart, char, uart2, &Uart::RxInterruptHandler>      uart2_callback;

//********************************
// Test it out.
//********************************
int main()
{

  // Setup the callbacks.
  timer1_callback   = &timer_member_callback;
  timer2_callback   = &timer_static_callback;
  timer3_callback   = &free_callback;
  uart1_rx_callback = &uart1_callback;
  uart2_rx_callback = &uart2_callback;

  // Simulate the interrupts.
  Timer1Interrupt();
  Timer2Interrupt();
  Timer3Interrupt();
  Uart1RxInterrupt();
  Uart2RxInterrupt();

  return 0;
}