September 2006 - Boost - lists.boost.org

Re: [boost] Work that has been done on Unicode
by Hartmut Kaiser 21 Sep '06

21 Sep '06

> Peter Dimov wrote: > > > You need the C standard to get the complete picture; it states that > > USHRT_MAX is at least 65535. > > The corresponding section of the C Standard you're referring > to states [Appendix E:1, implementation limits (informative)]: > > The contents of the header <limits.h> are given below, in > alphabetical order. The minimum magnitudes shown shall be > replaced by implementation-defined magnitudes with the same sign. > > So no restriction imposed from the Standard here, AFAIU. Ok, I found it. You're right. It's in the C Standard: 5.2.4.2.1 Sizes of integer types <limits.h>: maximum value for an object of type unsigned short int USHRT_MAX 65535 // 2^16 - 1 Sorry for the noise. Regards Hartmut

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[fusion] Extension docs
by David Abrahams 21 Sep '06

21 Sep '06

They could be made simpler (avoiding a few specializations) if you didn't try to do an nonintrusive example. E.g., this stuff: template <class Iterator> struct apply; // never defined template <class Struct, int index> struct apply<foobar<Struct,index> > { ... }; -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[Boost Conference] Save the Date
by David Abrahams 21 Sep '06

21 Sep '06

================================ Save the Date: May 14-18, 2007 ================================ We're pleased to issue this pre-announcement of the first annual Boost Conference, BoostCon 2007. The conference will take place in Aspen, Colorado, May 14-18. This promises to be the main face-to-face event for all things Boost, from from using Boost libraries to writing them, from evangelizing Boost to deployment within your organization, from infrastructure and process to vision and mission, and from TR1 to TR2. Given the range and interests of the participants, this event promises to be intense and in-depth. Due to the breadth of our community, the conference will be organized into two primary tracks: one directed mostly at hard-core Boost developers, and the other focused on the practical interests of Boost end-users. In the spirit of Boost, however, the conference will be planned to foster collaboration and interaction both within *and* across these tracks, with an emphasis on hands-on, participatory sessions. More details, including a call for session proposals, will be forthcoming in the next few weeks. Enrollment for this event will be limited, so we're issuing this notice to the Boost community well in advance. In the meantime, we have set up a page on the Boost Wiki where we're doing an informal, preliminary survey of interest (http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?BoostCon) If you want to be a part of the inaugural BoostCon and are likely to attend, we'd appreciate it if you'd add yourself (or an alias) to the list there, to help us with event planning. Thanks, The BoostCon 2007 Organizers ------------------------------------------------------------------ David Abrahams Beman Dawes Jeff Garland Kevlin Henney Scott Meyers Eric Niebler Sean Parent Rene Rivera Jeremy Siek Matthias Troyer ------------------------------------------------------------------

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[fusion] Easier extension
by David Abrahams 21 Sep '06

21 Sep '06

Wouldn't extension be a lot easier if iterator_base and sequence_base took (optional) 2nd arguments that specify the tag? Then you wouldn't need that whole dance that enables tag dispatching (right?) http://boost-consulting.com/boost/libs/fusion/doc/html/fusion/extension.htm… -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[fusion] more doc nits
by David Abrahams 21 Sep '06

21 Sep '06

http://boost-consulting.com/boost/libs/fusion/doc/html/fusion/support/categ… doesn't make it clear which namespace or header the traversal tags can be found in. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[fusion] defining tags
by David Abrahams 21 Sep '06

21 Sep '06

Is it intentional that http://boost-consulting.com/boost/libs/fusion/doc/html/fusion/extension.html suggests defining the new sequence tag in namespace boost::fusion? If so, why are you doing that? Inviting people to add definitions in the library's namespace is usually a bad idea. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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Re: [boost] Geometry/Vector Lib
by james.jones＠firstinvestors.com 21 Sep '06

21 Sep '06

From: "Olivier Grant" <olivier.grant(a)gmail.com> On 9/20/06, Walter Landry <wlandry(a)ucsd.edu> wrote: > > This seems wrong. If I want to add a vector2d to a vector3d, then I > > should have to do it manually. Otherwise, it should be a type error. > > it depends how you see the problem I suppose. A 2D vector is just a 3D > vector with z == 0. A 3D vector is a 4D vector with w == 1. And so on by > extension. Since these vector classes are not supposed to be used in a > polymorphic way, each argument of a function call is well-known by the user > - or at least should be :) - so I would not raise an exception in the case > of the use of two vectors with different dimensions. But a 2D vector is NOT just a 3D vector with z = 0!! It might sit in a subspace of a 3D vector space, but not necessarily in the z=0 plane. It could just as easily be a 2D vector in the x - 2y + 3z = 0 plane. Certainly do it this way if you want to - maybe it makes perfect sense for your particular application. But I'd never want to see something like this standardized in BOOST. It just ain't right. :) Also, if a 2D vector is a 3D vector with z=0, and a 3D vector is a 4D vector with w=1, "and so on by extension", then how would a 4D vector compare with a 5D vector? I don't get the extension. When you first posted your example, I assumed you'd made a typo when you set w=1, but now I think you did that on purpose. Why wouldn't w=0? - James Jones Administrative Data Mgmt. Webmaster 375 Raritan Center Pkwy, Suite A Data Architect Edison, NJ 08837

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Re: [boost] Geometry/Vector Lib
by Olivier Grant 21 Sep '06

21 Sep '06

On 9/20/06, Walter Landry <wlandry(a)ucsd.edu> wrote: > > "Olivier Grant" <olivier.grant(a)gmail.com> wrote: > > Hi, > > > > I have written a bit of code to handle geometric vectors in a generic > way, > > abstracting their dimension. The idea behind this code is to be able to > > apply one operation between two vectors, or a vector and a scalar, > whatever > > their dimension, and writing it in an expandable way without having to > > modify any manipulation functions if a new geometric vector class is > > created. The other advantage is that the resulting assembly code is just > as > > fast as if the functions had all been explicitly written. > > Does this hold true if the equations get complicated (e.g. products of > products)? Not yet, currently the code was really a test to find a way to allow any type of binary function to be applyed between vectors of different dimensions and/or scalar values. > Right now I have three simple vector classes - ranging from vector2d to > > vector4d - that are not templetized since I like the idea of being able > to > > access coordinates directly by their name > > > > vector3d vec; > > vec.x += 10.0f; > > > > to give you an example of the syntax, here is how you would add two > vectors > > of different dimensions : > > > > vector2d v1(1.0f, 2.0f); > > vector3d v2(-1.0f, 3.0f, 2.0f); > > vector4d res; > > > > vector_add(v1, v2, res); > > /* res now contains (0.0f, 5.0f, 2.0f, 1.0f) */ > > This is a bit clunky. What about using the operator+() and operator=()? You could just wrap vector_add in an operator+, but the original intension was to provide not only a generic way of handling any type of binary operation between vectors and/or scalars, but also to have it compile to the most efficient code possible. I also wanted to allow the user to know exactly what he is doing when performing function calls : res = v1 * scalar + v2; I think the following syntax really makes you sure you control what is happening : vector_mul(v1, scalar, v1); vector_add(v1, v2, res); In highly sensitive software that needs to perform very fast, I think developers would prefer this kind of syntax. The other advantage I see is to easily allow developers to use this function as a default implementation eventually replacing it with a architecture specific version if necessary/possible. > the result is determined by the dimension of the third vector passed to > > vector_add. > > v1 is auto-promoted to act like a vector3d. > > This seems wrong. If I want to add a vector2d to a vector3d, then I > should have to do it manually. Otherwise, it should be a type error. it depends how you see the problem I suppose. A 2D vector is just a 3D vector with z == 0. A 3D vector is a 4D vector with w == 1. And so on by extension. Since these vector classes are not supposed to be used in a polymorphic way, each argument of a function call is well-known by the user - or at least should be :) - so I would not raise an exception in the case of the use of two vectors with different dimensions. > v2 does not change. > > res gets (v1.x + v2.x, v1.y + v2.y, v1.z + v2.z , default_w_value). > > > > I didn't seem to find any information on a lib currently under > development > > that provides geometric vector manipulation in that way - maybe apart > from > > uBLAS - so I thought I would share this if anyone seems to be > interested. > > What are the advantages of this library over tvmet[1]? No idea! :) I didn't know of that library's existance but will definitely study it with much interest and give you that answer after if you're still interested. Cheers, > Walter Landry > wlandry(a)ucsd.edu > > [1] http://tvmet.sourceforge.net/ > Thanks for your comments/questions, Olivier.

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Re: [boost] shared_ptr : how to build object chain shared_ptr down and weak_ptr up in object ctor?
by Sebastian Redl 20 Sep '06

20 Sep '06

On Wed, September 20, 2006 11:48 am, Tom Titchener wrote: > > I'd like to build a chain of objects with an upper layer holding a > shared_ptr to a lower layer and the lower layer holding a weak_ptr back > to the upper layer. The upper layer users the shared_ptr for control. The > lower layer uses the weak_ptr for callbacks (first calling lock to > convert it to a shared_ptr). And ... I'd like to do it in my class ctors. > That's the kicker. It *seems* like the shared_from_this framework should > give me what I want... > I can't solve your particular problem, but it seems to be that using a weak pointer is the wrong solution in your example code. The callback is a member of the control, and thus cannot outlive it. In other words, the weak pointer ought to be superfluous - use an ordinary pointer. If the callback can actually outlive the control, then it shouldn't be the control that creates it. External code should create the callback and pass it the shared_ptr to an existing control. Sebastian Redl

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[mpl] Crossing More Runtime Boundaries
by Eric Lemings 20 Sep '06

20 Sep '06

Currently, the integral constant wrappers (integral_c, int_, etc.) have a function call operator that returns the runtime value of the type. Naturally, the metafunctions for arithmetic operations inherit these operators. Example: typedef plus< int_<1>, int_<2> > t1; assert (t1() == 3); What if MPL took this a step further and extended the placeholders concept to account for runtime parameters? The plus class template would then have a function call operator that accepts zero or more arguments depending on the number of placeholders. Some examples: typedef plus< int<1>, _ > t2; assert (t2(2) == 3); typedef plus< _, _ > t3; assert (t3(1, 2) == 3); typedef plus< _, plus< _, int_<-1> > > t4; assert (t4(1) == 1); With a metafunction to count placeholders in a lambda expression and some template specialization, I believe this is quite feasible. It would be useful for combining MPL arithmetic operations into more complex metafunctions that mix integral constants with runtime arguments. Thoughts? Thanks, Eric.

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