Christopher Haster / funcptr

Flexible templated function class and related utilities that avoid dynamic memory allocation without limiting functionality

Dependents:   SimpleHTTPExample

FuncPtr provides a flexible templated function class and related utilities while avoiding dynamic memory allocation and avoiding limited functionality.

FuncPtr provides an intuitive template interface:

FuncPtr<void(const char *)> func(puts);
func("hello!\n"); // prints hello!


Several function types are supported by FuncPtr:

// Simple C functions
void func();
FuncPtr<void()> fp(func);

// C++ Methods
struct Thing { void func(); };
Thing thing;
FuncPtr<void()> fp(&thing, &Thing::func);

// C functions with context
void func(Thing *);
FuncPtr<void()> fp(&thing, func);

// Function objects
struct Thing { void operator()(); };
Thing thing;
FuncPtr<void()> fp(&thing);


There is no dynamic memory allocation, managing memory is placed entirely on the user. More advanced function manipulation can be accomplished with statically allocated classes:

// Function binding
Binder<void(const char *), const char *> bind(putc, "hi!");
bind(); // prints hi!

// Function composition
Composer<int(const char *), const char *(int)> comp(puts, itoa);
comp(10); // prints 10

// Function chaining
Chainer<void(const char *), 2> chain;
chain.attach(puts);
chain.attach(puts);
chain("hi!\n"); // prints hi! twice


FuncPtr allows easy support of a large range of function types in C++ APIs with very few lines of code:

class Thing {
public:
    // The following two methods are sufficient for supporting 
    // every supported function type
    void attach(FuncPtr<void()> func) {
        _func.attach(func);
    }

    template<typename T, typename M>
    void attach(T *obj, M method) {
        attach(FuncPtr<void()>(obj, method));
    }

private:
    FuncPtr<void()> _func;
}


Additionally, FuncPtrs have several utilities for easy integration with C APIs:

// C style callbacks
void register_callback(void (*callback)(void *), void *data);

register_callback(&FuncPtr<void()>::thunk, &func);

// C style functions without context
void register_callback(void (*callback)());

Thunker thunk(func);
register_callback(thunk);

// mbed style callbacks
void register_callback(T *obj, void (T::*M)());

register_callback(&func, &FuncPtr<void()>::call);

Thunker.h

Committer:
Christopher Haster
Date:
2016-04-17
Revision:
18:a0fde14b6c39
Parent:
14:79be4e700cc9

File content as of revision 18:a0fde14b6c39:

/*  Thunker
 *  Thunk generating class for calling function objects through
 *  context-less functions
 */
#ifndef THUNKER_H
#define THUNKER_H

#include "FuncPtr.h"

extern "C" {
#include "trampoline.h"
}


/** Thunk generating class for calling function objects
 */
class Thunker {
public:
    /** Create a Thunker around a function
     */
    Thunker(FuncPtr<void()> func = 0) {
        attach(func);
        _entry = reinterpret_cast<void(*)()>(
            trampoline_init(&_trampoline, &Thunker::thunk, this));
    }

    /** Create a Thunker around a method
     */
    template <typename T, typename M>
    Thunker(T *obj, M method) {
        attach(obj, method);
        _entry = reinterpret_cast<void(*)()>(
            trampoline_init(&_trampoline, &Thunker::thunk, this));
    }

    /** Attach a function
     */
    void attach(FuncPtr<void()> func) {
        _func.attach(func);
    }

    /** Attach a method
     */
    template <typename T, typename M>
    void attach(T *obj, M method) {
        attach(FuncPtr<void()>(obj, method));
    }

    /** Call the attached function
     */
    void call() {
        return _func();
    }

    /** Call the attached function
     */
    void operator()() {
        return call();
    }

    /** Test if function has be attached
     */
    operator bool() const {
        return _func;
    }

    /** Static thunk for passing as C-style function
     *  @param func Thunker to call passed as void pointer
     */
    static void thunk(void *func) {
        return static_cast<Thunker*>(func)->call();
    }

    /** Entry point into thunk into function
     */
    entry_t *entry() {
        return _entry;
    }

    /** Entry point into thunk into function
     */
    operator entry_t*() {
        return entry();
    }

private:
    entry_t *_entry;
    trampoline_t _trampoline;
    FuncPtr<void()> _func;
};


#endif