On Mon, Aug 23, 2010 at 7:48 AM, Pierre Morcello <pmorcell-cppfrance@yahoo.fr> wrote:
Lorenzo Caminiti wrote :
Is there interest in a library that implement local functions for C++?
One year ago, I made a proposition for a boost.breakable. Some people were interested in the library, if I could widen it a little. David Abraham & Vicente Botet expressed interest in a macro local function that would work like scope exist.
So I wrote a first implementation. But I have not posted back on this subject, because I was unsure about the macro interface, since a few variations on its interface (ex: passing this or not) could be done.
Here I send 2 little examples of my tests. The 'V3' is almost the same as the one you posted. The 'V4' is a try wich uses only 1 macro call. Unfortunately, these 2 use currently __VA_ARGS__, and were only tested on visual 2008.
But yes, there is an interest in a local function.
I can implement Boost.LocalFunction macros, which are similar to your 'V3' macros, in pure C++ ISO standard (no __VA_ARGS__). I will study your code more. On Sun, Aug 22, 2010 at 9:27 PM, Jeffrey Lee Hellrung, Jr. <jhellrung@ucla.edu> wrote:
On 8/22/2010 6:01 PM, OvermindDL1 wrote:
On Sun, Aug 22, 2010 at 11:18 AM, Mathieu -<ptr.jetable@gmail.com> wrote:
I might be totally wrong here but I don't see how it's different from lambdas...
What can it do differently from boost::phoenix? I am guessing you just create and instance a struct right there, but boost::phoenix would be more succinct.
Except Boost.Phoenix isn't as expressive as "real" C++, is it? E.g., local variables are somewhat clumsy (opinion) in the current incarnation of Boost.Phoenix.
Also, it seems reasonable to implement BOOST_LOCAL_FUNCTION in terms of lambdas if they exist, but perhaps one would want to use local functions on non-lambda-enabled compilers.
I am NOT an expert of Boost.Phoenix and Boost.Lambda so *please correct me if I am wrong*. I think the main different between using Boost.Phoenix or Boost.Lambda and using Boost.LocalFunction is that in Boost.LocalFunction the local function body completely retains C++ syntax (a part from using `this_` instead of `this`... which is not ideal...). Now this might or it might not be a problem. For example, in my Boost.Contract application I need the users to write the local function body and pass it to a macro so it is a requirement for that body to be written in usual C++ because I cannot request Boost.Contract users to learn Boost.Phoenix or Boost.Lambda. However, for other applications using Boost.Phoneix or Boost.Lambda might be fine. I think C++0x lambdas will be a valid option in replacing Boost.LocalFunction but they are only part of *new* C++ standard and not supported by all compilers. -- Lorenzo