Refactor core::char::EscapeDefault and co. structures by mina86 · Pull Request #105076 · rust-lang/rust (original) (raw)

Change core::char::{EscapeUnicode, EscapeDefault and EscapeDebug}
structures from using a state machine to computing escaped sequence
upfront and during iteration just going through the characters.

This is arguably simpler since it’s easier to think about having
a buffer and start..end range to iterate over rather than thinking
about a state machine.

This also harmonises implementation of aforementioned iterators and
core::ascii::EscapeDefault struct. This is done by introducing a new
helper EscapeIterInner struct which holds the buffer and offers simple
methods for iterating over range.

As a side effect, this probably optimises Display implementation for
those types since rather than calling write_char repeatedly, write_str
is invoked once. On 64-bit platforms, it also reduces size of some of
the structs:

| Struct                     | Before | After |
|----------------------------+--------+-------+
| core::char::EscapeUnicode  |     16 |    12 |
| core::char::EscapeDefault  |     16 |    12 |
| core::char::EscapeDebug    |     16 |    16 |

My ulterior motive and reason why I started looking into this is
addition of as_str method to the iterators. With this change this
will became trivial. It’s also going to be trivial to implement
DoubleEndedIterator if that’s ever desired.