According to #7887, we've decided to use the syntax of `fn map<U>(f: &fn(&T) -> U) -> U`, which passes a reference to the closure, and to `fn map_move<U>(f: &fn(T) -> U) -> U` which moves the value into the closure. This PR adds these `.map_move()` functions to `Option` and `Result`.
In addition, it has these other minor features:
* Replaces a couple uses of `option.get()`, `result.get()`, and `result.get_err()` with `option.unwrap()`, `result.unwrap()`, and `result.unwrap_err()`. (See #8268 and #8288 for a more thorough adaptation of this functionality.
* Removes `option.take_map()` and `option.take_map_default()`. These two functions can be easily written as `.take().map_move(...)`.
* Adds a better error message to `result.unwrap()` and `result.unwrap_err()`.
Change the former repetition::
for 5.times { }
to::
do 5.times { }
.times() cannot be broken with `break` or `return` anymore; for those
cases, use a numerical range loop instead.
Implement RAI where possible for iterator adaptors such as Map,
Enumerate, Skip, Take, Zip, Cycle (all of the requiring that the adapted
iterator also implements RAI).
Drop the "Iterator" suffix for the the structs in std::iterator.
Filter, Zip, Chain etc. are shorter type names for when iterator
pipelines need their types written out in full in return value types, so
it's easier to read and write. the iterator module already forms enough
namespace.
With the recent fixes to method resolution, we can now remove the
dummy type parameters used as crutches in the iterator module.
For example, the zip adaptor type is just ZipIterator<T, U> now.
This implements the trait for vector iterators, replacing the reverse
iterator types. The methods will stay, for implementing the future
reverse Iterable traits and convenience.
This can also be trivially implemented for circular buffers and other
variants of arrays like strings and `SmallIntMap`/`SmallIntSet`.
The `DoubleEndedIterator` trait will allow for implementing algorithms
like in-place reverse on generic mutable iterators.
The naming (`Range` vs. `Iterator`, `Bidirectional` vs. `DoubleEnded`)
can be bikeshedded in the future.
flat_map_ produces an iterator that maps each element to an iterator,
and yields the elements of the produced iterators.
This is the monadic bind :: M a -> (a -> M b) -> M b for iterators.
Named just like the vec method, but with a trailing underline until the
method resolution bug is resolved.
We discussed the name chain_map, but I decided to go with flat_map_ for consistency with vec.
Since it.map(f).flatten() would be the same as it.flat_map(f), we could choose
to just implement a flatten method instead. Either way the possibilities are the same but flat_map is more convenient.
flat_map_ produces an iterator that maps each element to an iterator,
and yields the elements of the produced iterators.
This is the monadic bind :: M a -> (a -> M b) -> M b for iterators.
Named just like the vec method, but with a trailing underline until the
method resolution bug is resolved.
