This switches out the `<variant/optional.hpp>` implementation of the
optional monad to the one from Boost.
The following trick makes sure we keep compile times down:
- use `<boost/optional/optional_fwd.hpp>` to forward declare the
optional type in header, then include the full blown optional header
only in the implementation file.
- do the same for the files we touch, e.g. forward declare osmium types,
allowing us to remove the osmium header dependency from our headers:
`namespace osmium { class Relation; }
and then include the appropriate osmium headers in the implementation
file only. We should do this globally...
References:
- http://www.boost.org/doc/libs/1_59_0/libs/optional/doc/html/index.html
- https://github.com/osmcode/libosmium/issues/123
This caches iterators, i.e. especially the end iterator when possible.
The problem:
for (auto it = begin(seq); it != end(seq); ++it)
this has to call `end(seq)` on every iteration, since the compiler is
not able to reason about the call's site effects (to bad, huh).
Instead do it like this:
for (auto it = begin(seq), end = end(seq); it != end; ++it)
caching the end iterator.
Of course, still better would be:
for (auto&& each : seq)
if all you want is value semantics.
Why `auto&&` you may ask? Because it binds to everything and never copies!
Skim the referenced proposal (that was rejected, but nevertheless) for a
detailed explanation on range-based for loops and why `auto&&` is great.
Reference:
- http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3853.htm
* Adds a data structure, RasterSource, to store parsed + queryable data
* Adds bindings for that and relevant data structures as well as source_function and segment_function
* Adds relevant unit tests and cucumber tests
* Bring-your-own-data feature
