Find a good syntax for expressing ranges

[dsharlet]

The current interval/range syntax is pretty verbose. It would be great to be able to write something like a(x0:x1, y0:y1, z) to crop x, y and slice z, similar to numpy style. In C++ we are more limited. The current syntax is something like a(interval(x0, x1), interval(y0, y1), z), or a(range<>(x0, x1 - x0), range<>(y0, y1 - y0), z).

Possible options I can think of are:

• Some single-letter helper function V(begin, end): a(V(x0, x1), V(y0, y1), z). If you have an active imagination, V is kind of like the for-all symbol...
• If x0, y0 where some kind of class, we could do some crazy (and possibly expensive) trick with operator->: a(x0 -> x1, y0 -> y1, z). It is unreasonable to require x0, y0 to be a particular type though.

Some additional thoughts:

• Both intervals and ranges are important. Ranges are useful because compile-time constant extents are possible (hence the template for range<>).
• Global operators can't be overloaded for index-like types, so we couldn't do something like make x0 > x1 return a bool_or_range implicitly convertible type. Nor should we...

[jiawen]

How about:

• nda::range(begin, end) for the verbose version.
• using nda::r = nda::range as a shorthand. It will harken to R"" for raw strings.

nda::all() or nda::slice() can also be shorthands the equivalent of ":" in Python when reading.

[dsharlet]

I decided to go ahead and use your suggestion. I already had a function interval that was exactly your suggestion, and range was the object that interval produced. I basically swapped those names, and added r to make it less verbose.

I also added all, which is an alias for _, which already existed.

[dsharlet]

I'm going to close this because this is C++ and I don't see any realistic and not ultra-hacky way to make this any better than short function names.