Question

Possible Duplicate:
Clang, std::shared_ptr and std::less/operator<

So yeah, the title is pretty much the whole problem. As you can see from the snippet below i did implement operator< so i have no idea of what’s going on.

Here is the code:

namespace {

struct Transition {
    string name;
    StatePtr toState;

    Transition(string s = string(), StatePtr state = nullptr)
      : name(move(s))
      , toState(move(state))
    {}

    friend bool operator==(Transition const& lhs, Transition const & rhs) {
      return lhs.name == rhs.name && lhs.toState == rhs.toState;
    }

    friend bool operator<(Transition const & lhs, Transition const & rhs);
  };

  struct State {
    string name;
    set<TransitionPtr> transitions;

    explicit State(string s = string())
      : name(move(s))
    {}

    void addTransition(string s, StatePtr sp = nullptr){
      TransitionPtr new_t = make_transition(s, sp);
      for(auto& t : transitions){
        if(t == new_t){
          return;
        }
      }

      transitions.insert(move(new_t)); // This is where the error happens.
    }

  };
}

bool operator<(StateMachine::Transition const & lhs, StateMachine::Transition const & rhs) {
 return lhs.toState.get() < rhs.toState.get();
}

and the error message is:

In file included from ../llvm_opt_pass/cgd.cpp:3:
In file included from /srv/scratch/sigubufo/clang/stable/3.1_src/llvm/include/llvm/Instructions.h:23:
In file included from /srv/scratch/sigubufo/clang/stable/3.1_src/llvm/include/llvm/ADT/ArrayRef.h:13:
In file included from /srv/scratch/sigubufo/clang/stable/3.1_src/llvm/include/llvm/ADT/SmallVector.h:24:
In file included from /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/memory:85:
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:486:14: error: no matching function for call to object of type ‘std::less<_CT>’
return std::less<_CT>()(__x.get(), __y.get());
^~~~~~~~~~~~~~~~

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/stl_function.h:237:20: note: in instantiation of function template specialization ‘std::operator<<::StateMachine::Transition, std::default_delete<::StateMachine::Transition>, ::StateMachine::Transition, std::default_delete<::StateMachine::Transition> >’ requested here
{ return __x < __y; }
^

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/stl_tree.h:1285:13: note: in instantiation of member function ‘std::less::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > >::operator()’ requested here
__comp = _M_impl._M_key_compare(_KeyOfValue()(__v), _S_key(__x));
^

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/stl_set.h:424:9: note: > in instantiation of function template specialization ‘std::_Rb_tree::StateMachine::Transition, std::default_delete<::StateMachine::Transition> >, std::unique_ptr<::StateMachine::Transition, std::default_delete<::StateMachine::Transition> >, std::_Identity::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > >, std::less::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > >, std::allocator::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > > ::_M_insert_unique::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > >’ requested here
_M_t._M_insert_unique(std::move(__x));
^

../llvm_opt_pass/cgd.cpp:72:17: note: in instantiation of member function ‘std::set::StateMachine::Transition, std::default_delete<::StateMachine::Transition> >, std::less::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > >, std::allocator::StateMachine::Transition, std::default_delete<::StateMachine::Transition> > > >::insert’ requested here
transitions.insert(move(new_t));
^

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/stl_function.h:236:7: note: candidate function not viable: no known conversion from ‘pointer’ (aka ‘::StateMachine::Transition *’) to ‘::StateMachine::Transition *&&&’ > for 1st argument;
operator()(const _Tp& __x, const _Tp& __y) const

Answer 1

Ok, so the solution is the same as to this question: Clang, std::shared_ptr and std::less/operator< .

Basically it’s a bug in type_traits from libstdc++.