Re: [boost] [future] direct construct from value

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-05-16 10:13:09

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Friday 16 May 2008 05:14 am, Johan Torp wrote:
> Frank Mori Hess wrote:
> > I've just noticed that neither Anthony's or Braddock's future libraries
> > seem
> > to support construction of a future directly from a value, like
> >
> > future<int> fut_int(5);
> >
> > Adding such a constructor gives support for implicit conversion of a
> > value of
> > type T to a future<T>.  So a function which takes futures as arguments
> > can also seamlessly accept values:
> >
> > future<void> my_func(future<int> f1, future<int> f2);
> >
> > my_func(fut_int, 3);
>
> Adding an explicit constructor is one thing. Allowing implicit type
> conversions is more dangeous and needs to be thought through carefully.
> Could you make do with explicit constructing?
>
> my_func(fut_int, future<int>(3));

Can you come up with any specific examples of how implicitly constructing a 
ready future from a value would be dangerous?  It's not like implicity 
constructing a shared_ptr from a raw pointer, which might cause the raw 
pointer to be accidentally deleted.  It's certainly less dangerous than going 
the other direction (which has generated some controversy): implicit 
conversion of a future to a value, which can block.  Note, I'm not suggesting 
adding support for direct assignment from the template type.  I certainly 
wouldn't make the poet::future constructor explicit and diminish useability 
without a concrete reason for doing so.

- -- 
Frank
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQFILZZ15vihyNWuA4URAnJIAJoDjRHtgNAAQ4Bm15AislS4kzg1tgCdG2pg
DG/tpcYd4QldDsViLlL9/hw=
=jdVL
-----END PGP SIGNATURE-----