flyweight: multiple default constructors with real perfect forwarding

[tore.halvorsen@…]

Flyweight gets two default constructors, since it has a direct default constructor

flyweight():h(core::insert()){}

and one based on variable template arguments, which can be zero.

#define BOOST_FLYWEIGHT_PERFECT_FWD_CTR_BODY(args) \
  :h(core::insert(BOOST_FLYWEIGHT_FORWARD(args))){}

  BOOST_FLYWEIGHT_PERFECT_FWD_WITH_ARGS(
    explicit flyweight,
    BOOST_FLYWEIGHT_PERFECT_FWD_CTR_BODY)

#undef BOOST_FLYWEIGHT_PERFECT_FWD_CTR_BODY

which can expand to:

template<typename... Args>
explicit flyweight(Args&&... args) 
:h(core::insert(std::forward<Args>(args)...)){}

[Joaquín M López Muñoz]

As far as I understand C++ rules, this should not raise any kind of ambiguity as the default ctor should be preferred over the templated ctor (called with no args). Are you having warnings with some compiler?

[tore.halvorsen@…]

Replying to joaquin:

As far as I understand C++ rules, this should not raise any kind of ambiguity as the default ctor should be preferred over the templated ctor (called with no args). Are you having warnings with some compiler?

I get warnings from MS Visual Studio 2013.

You are probably right in that the default ctor is preferred. It's probably just a cosmetic warning.

[Joaquín M López Muñoz]

OK, I'll fix it then tonight if I have a moment to spare. Can I count on your support to verify that the warning goes away after I do the commit?

[tore.halvorsen@…]

Replying to joaquin:

OK, I'll fix it then tonight if I have a moment to spare. Can I count on your support to verify that the warning goes away after I do the commit?

Sure :)

[Joaquín M López Muñoz]

Here you are:

​https://github.com/boostorg/flyweight/commit/8f5bbd5d57780fd33e3b527a3d406e14a4d0fd9d

Could you please report back if the warning is gone?

[Joaquín M López Muñoz]

I've decided to revert the previous fix as it changes (theoretically at least) boost::flyweight public interface, and used #pragma warning(disable:4520) instead:

​https://github.com/boostorg/flyweight/commit/095dcfb812ab8670af70912419e129d9ad656927

Can you check this works also? Thank you.

[tore.halvorsen@…]

The first worked - I'll check the second :)

[tore.halvorsen@…]

The pragma works as well.