bind fwds shared_ptr twice, invokes memfn with nullptr

[Jason Mancini <jayrusman@…>]

Behavior started in 1.60, due to bind/bind.hpp changes around forwarding and rvalues. Short sample is shown below. This limitation needs to be mentioned in the boost docs, or somehow alter bind to work like before. Bind 1.59 would print the ptr address twice. Bind 1.60 gets a nullptr on the second memfn call. Quick fix for this sample is to change tFunc to use shared_ptr<...>const& such that it can't be forwarded.

#include <stdio.h>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <boost/bind.hpp>
#include <boost/function.hpp>

using namespace boost;
using tFunc = function<bool(shared_ptr<const Obj>)>;

struct Obj { bool MF() const { printf("this %p\n", this); return true; } };

int main() {
  shared_ptr<const Obj> sptr = make_shared<Obj>();
  tFunc BB;
  BB = bind(&Obj::MF, _1);
  BB = bind(BB, _1) && bind(&Obj::MF, _1);
  BB(sptr);
}

Boost 1.59

this 0x117fc39
this 0x117fc39

Boost 1.60

this 0x117fc39
this (nil)

[Jason Mancini <jayrusman@…>]

Let's try that code sample again. :^{) Slightly adjusted for clarity.}

#include <stdio.h>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <boost/bind.hpp>
#include <boost/function.hpp>

using namespace boost;
struct Obj { bool MF() const { printf("this %p\n", this); return true; } };
using tFunc = function<bool(shared_ptr<const Obj>)>;

int main() {
  shared_ptr<const Obj> sptr = make_shared<Obj>();
  tFunc AA, BB;
  AA = bind(&Obj::MF, _1);
  BB = bind(AA, _1) && bind(&Obj::MF, _1);
  BB(sptr);

[Jason Mancini <jayrusman@…>]

}

[Peter Dimov]

Thanks for the report; should be fixed in ​https://github.com/boostorg/bind/commit/6616add21dff43f573d51503ebad4d3fcbcb2619

[Jason Mancini <jayrusman@…>]

Wow quick turn-around! Confirmed fix works for both the sample and the actual application. Thanks!

[Peter Dimov]

Merged to master.