* TODO trait to separate visibility of methods from visibility of data (https://github.com/sfackler/rust-postgres/blob/master/src/lib.rs#L1400)
* TODO Deref on Vec/String to treat like a smart pointer/borrowed view of such data
* TODO leak amplification ("Vec::drain sets the Vec's len to 0 prematurely so that mem::forgetting Drain "only" mem::forgets more stuff. instead of exposing uninitialized memory or having to update the len on every iteration")
* TODO dtor for finally
* TODO interior mutability - UnsafeCell, Cell, RefCell
* TODO closures and lifetimes (coupling to lifetime)
* TODO platform-specific sub-modules (https://github.com/rust-lang/rfcs/blob/master/text/0517-io-os-reform.md#platform-specific-opt-in)
* TODO affine types/session types
* TODO Entry API vs insert_or_update etc.
* TODO visitor
* TODO fold
* TODO small crates and semver
* TODO extension traits
* TODO destructor bombs (ensure linear typing dynamically, e.g., https://github.com/Munksgaard/session-types/commit/0f25ccb7c3bc9f65fa8eaf538233e8fe344a189a)
* TODO convertible to Foo trait for more generic generics (e.g., http://static.rust-lang.org/doc/master/std/fs/struct.File.html#method.open)
* TODO late binding of bounds for better APIs (i.e., Mutex's don't require Send)
* TODO 'shadow' borrowed version of struct - e.g., double buffering, Niko's parser generator
* TODO composition of structs to please the borrow checker