`max_by` method returns the element that gives the maximum value from the specfied function.
`max_by`/`min_by` are convenient when you want to get the value which has greatest/smallest scores.
Inspired by [ruby's Enumerable module](http://ruby-doc.org/core-2.0/Enumerable.html).
Add method .move_from() to MutableVector, which consumes another vector
and moves elements into the receiver.
Add new trait MutableCloneableVector with one method .copy_from(), which
clones elements from another vector into the receiver.
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.
Reopening of #7031, Closes#6963
I imagine though that this will bounce in bors once or twice... Because attributes can't be cfg(stage0)'d off, there's temporarily a lot of new stage0/stage1+ code.
This adds a `#[no_drop_flag]` attribute. This attribute tells the compiler to omit the drop flag from the struct, if it has a destructor. When the destructor is run, instead of setting the drop flag, it instead zeroes-out the struct. This means the destructor can run multiple times and therefore it is up to the developer to use it safely.
The primary usage case for this is smart-pointer types like `Rc<T>` as the extra flag caused the struct to be 1 word larger because of alignment.
This closes#7271 and #7138
This sets the `get_tydesc()` return type correctly and removes the intrinsic module. See #3730, #3475.
Update: this now also removes the unused shape fields in tydescs.
