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);

Diff: Chainer.h

Revision:
18:a0fde14b6c39
Parent:
15:0c3d1c4a050b
--- a/Chainer.h	Wed Apr 20 02:43:14 2016 -0500
+++ b/Chainer.h	Sun Apr 17 23:38:04 2016 -0500
@@ -14,6 +14,76 @@
 
 /** Static function composition
  */
+template <typename A0, typename A1, typename A2, typename A3, typename A4, int N>
+class Chainer<void(A0, A1, A2, A3, A4), N> {
+public:
+    /** Access a function in the chain
+     */
+    FuncPtr<void(A0, A1, A2, A3, A4)> &operator[](int i) {
+        return _funcs[i];
+    }
+
+    /** Attach a function to the chain
+     */
+    bool attach(FuncPtr<void(A0, A1, A2, A3, A4)> func) {
+        for (int i = 0; i < N; i++) {
+            if (!_funcs[i]) {
+                _funcs[i].attach(func);
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /** Attach a function to the chain
+     */
+    template <typename T, typename M>
+    bool attach(T *obj, M method) {
+        return attach(FuncPtr<void(A0, A1, A2, A3, A4)>(obj, method));
+    }
+
+    /** Call each function in the chain
+     */
+    void call(A0 a0, A1 a1, A2 a2, A3 a3, A4 a4) {
+        for (int i = 0; i < N; i++) {
+            if (_funcs[i]) {
+                _funcs[i](a0, a1, a2, a3, a4);
+            }
+        }
+    }
+
+    /** Call each function in the chain
+     */
+    void operator()(A0 a0, A1 a1, A2 a2, A3 a3, A4 a4) {
+        return call(a0, a1, a2, a3, a4);
+    }
+
+    /** Test if any functions have been attached
+     */
+    operator bool() const {
+        for (int i = 0; i < N; i++) {
+            if (_funcs[i]) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /** Static thunk for passing as C-style function
+     *  @param func Chainer to call passed as void pointer
+     */
+    static void thunk(void *func, A0 a0, A1 a1, A2 a2, A3 a3, A4 a4) {
+        return static_cast<Chainer<void(A0, A1, A2, A3, A4), N>*>(func)
+                ->call(a0, a1, a2, a3, a4);
+    }
+
+private:
+    FuncPtr<void(A0, A1, A2, A3, A4)> _funcs[N];
+};
+
+/** Static function composition
+ */
 template <typename A0, typename A1, typename A2, typename A3, int N>
 class Chainer<void(A0, A1, A2, A3), N> {
 public: