Re: [boost] [range] [extensions] Default values for range access adaptors?

7 Jun 2013

      Hi Michel, Akira,

I think simpler solution would be to add range support for
boost::optional in additional header (e.g.
).
i.e. boost::optional will become random access range.

// OK
#include 
for (T x : r | optional_front()) {
  std::cout << x << std::endl
}

// also OK
if (optional<T> x = r | optional_front()) {
  std::cout << x.get() << std::endl;
}

// another example:
#include 
optional<int> x = 100;
assert(boost::size(x) == 1);
optional<int> y = boost::none;
assert(boost::size(y) == 0);

Thanks.

2013/6/6 Akira Takahashi :
...
Hi Michel,
2013/6/6 Michel Morin 
...
Akira Takahashi wrote:
...
My Boost.Range Extension has `front` accessor.
"Range Access" adaptors in your extensions are interesting.
For the consistency of range adaptors, shouldn't `front` adaptor
return `single` range?
I see. `optional_front` usage is following:
if (optional<T> x = r | optional_front()) {
  std::cout << x.get() << std::endl;
}
If `front` return signle range, the usage is following:
for (T x : x | front) {
  std::cout << x << std::endl;
}
If `front` is error, the return value is empty range.
I think single range approach is better. However, I think now `front` and
`optional_front` is useful.
I would like to add `optional_front` and `front_range`.
Thanks!
Akira
--
' Yusuke Ichinohe
' yusuke.ichinohe@gmail.com