24 May
2010
24 May
'10
1:15 p.m.
On Sun, May 23, 2010 at 10:53:59PM -0400, Paul Davis wrote:
On Sun, May 23, 2010 at 10:03 PM, Joshua D. Boyd
<jdboyd(a)jdboyd.net> wrote:
yeah. the functors are a point where c++ needs a language extension.
but the c++0x lambda is that.
and it really makes closures pretty painless and straight forward.
i dont really understand why a lambda is some obscure type that needs to
be converted to a std::function if you want to store them in a
container (this sounds a bit like java before generics ;)
but this probably to allow compiler to optimize something like this:
int total = 0;
std::vector<int> vec;
auto sum_up = [&](int v) { total += v; };
std::for_each( vec.begin(), vec.end(), sum_up );
std::cout << total;
--
torben Hohn
I think it isn't difficult to read because it is C++ or Boost. It is
difficult to read because it involves concepts like promises and futures,
which are advanced topics that a lot of people (myself included) aren't
adequately familiar with (at least not without referring to a cheat sheet).
If we rewrote that with C types using a C type future/promise system, I'm
not sure it would be any easier to read for those of us who don't
intuitively grok promises and futures.
what he said. we can extend this to a lot of boost-covered stuff. a C
implementation of boost::optional would be similarly opaque and clumsy, i
think.
i also can't begin to imagine how to implement scoped-lifetime objects in C.
even without exceptions (which admittedly do cause some conceptual pain in
C++), the ability to know that wherever you return from within a function,
relevant local objects will be cleaned up has a significant simplifying
effect on the design of a function.
so yes, you can certainly get along without these ideas and write very
sophisticated software. the issue is really about whether you want to. when
i went to write a functor class a few months ago, i got about 90% of the way
there in a few hours. then i went and read the boost headers and realized
there was an entire universe of semantic details that i was overlooking and
that to get all the way "there" would take me weeks, assuming i ever got
there. so i could (a) do without functors or (b) use the boost
implementation. i chose (a).