boost::packaged_task has invalid variadic signature

[Alexander Karzhenkov <karzhenkov@…>]

The following code doesn't compile:

#define BOOST_THREAD_VERSION 4

#include <boost/thread/future.hpp>

void func(int) { }

int main()
{
	boost::packaged_task<void(int)> task{func};
}

Compilation error is caused by the misuse of BOOST_THREAD_RV_REF macro. Constructor expects argument of type void(int&&) and can't accept func. There is similar issue with operator (). The file future.hpp needs to be patched:

diff --git a/include/boost/thread/future.hpp b/include/boost/thread/future.hpp
index e6e2236..e477535 100644
--- a/include/boost/thread/future.hpp
+++ b/include/boost/thread/future.hpp
@@ -2715,3 +2715,3 @@
 #if defined BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK && defined(BOOST_THREAD_PROVIDES_VARIADIC_THREAD)
-              typedef R (*CallableType)(BOOST_THREAD_RV_REF(ArgTypes) ... );
+              typedef R (*CallableType)(ArgTypes ... );
 #else
@@ -2946,3 +2946,3 @@
 #if defined BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK && defined(BOOST_THREAD_PROVIDES_VARIADIC_THREAD)
-            typedef void (*CallableType)(BOOST_THREAD_RV_REF(ArgTypes)...);
+            typedef void (*CallableType)(ArgTypes...);
 #else
@@ -3269,3 +3269,3 @@
 #if defined BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK && defined(BOOST_THREAD_PROVIDES_VARIADIC_THREAD)
-        void operator()(BOOST_THREAD_RV_REF(ArgTypes)... args) {
+        void operator()(ArgTypes... args) {
             if(!task) {

[viboes]

Hi, you are surely right. I will take a look soon.

[viboes]

It seems that the last change is not really needed.

-        void operator()(BOOST_THREAD_RV_REF(ArgTypes)... args) {
+        void operator()(ArgTypes... args) {

Please, could you confirm?

[Alexander Karzhenkov <karzhenkov@…>]

It's needed. Just try slightly modified test:

#define BOOST_THREAD_VERSION 4

#include <boost/thread/future.hpp>

void func(int) { }

int main()
{
	boost::packaged_task<void(int)> task{func};

	task(0);	// ok

	int x = 0;
	task(x);	// compile error: can't bind to rvalue reference
}

[viboes]

Agreed and applied ​https://github.com/boostorg/thread/commit/aafd5ca7265e9edea1f100df88eb90c7653a70fc

[viboes]

​https://github.com/boostorg/thread/commit/a3497e1ffceb14318ff09e339a53293926351057