Benjamin Bannier created MESOS-4995:
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Summary: Make it possible to directly defer invocations of const
member functions
Key: MESOS-4995
URL: https://issues.apache.org/jira/browse/MESOS-4995
Project: Mesos
Issue Type: Bug
Components: libprocess
Reporter: Benjamin Bannier
libprocess' {{defer}} provides the following overloads
{code}
Deferred<void()> defer(const Process<T>& process, void (T::*method)())
Deferred<void()> defer(const Process<T>* process, void (T::*method)())
Deferred<Future<R>()> defer(const PID<T>& pid, Future<R> (T::*method)())
Deferred<Future<R>()> defer(const Process<T>& process, Future<R> (T::*method)())
Deferred<void()> defer(const PID<T>& pid, void (T::*method)())
Deferred<Future<R>()> defer(const PID<T>& pid, R (T::*method)())
Deferred<Future<R>()> defer(const Process<T>& process, R (T::*method)())
Deferred<Future<R>()> defer(const Process<T>* process, R (T::*method)())
Deferred<Future<R>()> defer(const Process<T>* process, Future<R> (T::*method)())
_Deferred<Future<R>()> defer(const UPID& pid, F&& f)
{code}
Here all overloads but the last require that the first argument is (in a LSP
sense) either a {{Process<T>}} or a {{PID<T>}}, and only member functions of
{{T}} are supported. Consider the following setup,
{code}
struct Base : public Process<Base> {
double b() { return 0; } // non-const due to MESOS-XXXX
};
struct Derived : public Base {
double d() { return 0; } // non-const due to MESOS-XXXX
};
{code}
We can then {{defer}} for a {{Base}} like
{code}
defer(base, &Base::b);
{code}
which invokes an overload taking {{const Process<T>&}} and {{R
(T::*method)()}}, but on the other hand use of {{Derived}} is more cumbersome,
{code}
defer(derived.self(), &Derived::d);
{code}
This effectively performs an explicit cast of the {{Derived}} to a
{{PID<Derived}} so the overload taking {{const PID<T>&}} and {{R
(T::*method)()}} can be taken. The overload taking for the {{Base}} case cannot
be taken here since while {{Derived}} is a {{Process<Base>}}, there exists no
{{&Base::d}} (like one would have expected).
We should investigate ways to allow the same {{self}}-less {{defer}} syntax for
both {{Base}} and {{Derived}}-like classes. This might be possible by
decoupling the types {{T}} for the first and second arguments.
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