Lin, Yi-Li wrote:

I found that boost::value_factory did not accept rvalues in some case.

In my case, temporary value is produced and passed to value factory directly.

The documentation for Boost Functional/Factory states: 'For technical reasons the arguments to the function objects have to be LValues. A factory that also accepts RValues can be composed using the boost::forward_adapter or boost::bind.' Your suggestion of using const lvalue (passing in non-const reference wrappers where needed) seems to be the workaround for the C++03 perfect forwarding problem that was employed by Boost smart_ptr::make_shared, not sure why Functional/Factory took a different approach? Tom.