One limitation of C++ is that implicit casts do not occur when
matching template overloads, as a consequence the callback's
argument type requires a strict match.
Unfortunately, the prevents the previously common pattern of using
void pointers as function arguments, causing unnecessary problems
for users porting code.
Thing *t;
void doit(void *p) { blablabla }
Callback<void()> cb(t, doit);
To avoid this, explicit overloads on void pointers were added. This
avoids a template expansion, and allows the implicit cast to occur
as the user would expect.
- Marked `call` and `operator()` functions as const
- Moved to static_cast for internal function pointer to avoid losing
compiler checked const-safety
- Added test for `operator=` with non-callback types
- Moved from zero-cast to value-initializer when callback is null
- Added `operator==` and `operator!=`
- Removed special handling of null callback
- Replicated doxygen to all overloads
- Added correct nops where uninitialized callbacks are called
- Added assertion for null callback
- Removed copy-constructor from callback constructor
Additionally, the following changes were don to avoid combinatorial
explosion in function overloads as a result of adding cv-qualifiers:
- Added convenience function for inferred type
- Deprecated callback overloads qhere cv-qualifiers are not scalable
Supported overloads:
callback(void (*f)(A...));
callback(const Callback<R(A...)> &);
callback(T *t, void (*f)(T*, A...));
callback(const T *t, void (*f)(const T*, A...));
callback(volatile T *t, void (*f)(volatile T*, A...));
callback(const volatile T *t, void (*f)(const volatile T*, A...));
callback(T *t, void (T::*f)(A...));
callback(const T *t, void (T::*f)(A...) const);
callback(volatile T *t, void (T::*f)(A...) volatile);
callback(const volatile T *t, void (T::*f)(A...) const volatile);
Before, the following results in a compilation error:
const struct Object *obj;
void obj_doit(const Object *obj);
Callback<void()> cb(obj, obj_doit);
This is especially noticable when migrating from the old Thread
constructor, which previously _required_ const.
Short term fix for all cv qualifiers through a C cast:
void *_obj = (void*)obj;
per @c1728p9
Update the Callback class to handle a NULL thunk by returning 0
rather than trying to call the thunk. This fixes a crash that occurs
on some targets when the TX uart handler is not attached.
Background:
The K64F HAL uart implementation calls the TX interrupt handler
every time a uart interrupt occurs while the TX register is empty.
It does not check to see if the TX interrupt has been enabled.
This means that the TX interrupt can and typically does get
run on RX events. This causes a crash with the newer callback
code which did not (prior to this patch) support a NULL thunk.
- Adopt C++11 style template arguments, requires rename to Callback
- Add constructor for C style callback functions
- Add constructor for Callbacks
- Add static function for passing to C style callbacks
Christopher Haster
Russ Butler
Jimmy Brisson