CHANGE

A RustFest Carol

impl'ementing

A Ghost Story of RustFest

by

Felix S. Klock II (@pnkfelix)

with apologies to

Charles Dickens, David Foster Wallace, and Mark Z. Danielewski

This is a work of fiction. Names, characters, businesses, places, events and incidents are either the products of the author’s imagination or used in a fictitious manner. Any resemblance to actual persons, living or dead, or actual events is purely coincidental.

Matsakis' Ghost

IRC snippets

<manishearth> RIIR!
<pnkscrooge> Bah! Humbug!

Scrooge's optimism about Rust's future had faltered

<pnkscrooge> What’s Rust to you but a language
<pnkscrooge> for writing types without deploying apps;
<pnkscrooge> a language for finding yourself a compile-cycle older,
<pnkscrooge> but not an object file richer?
<pnkscrooge> If I could work my will,
<pnkscrooge> every idiot who goes about with "RIIR" on their lips
<pnkscrooge> should be nailed up in their own crate
<pnkscrooge> and buried with a bicycle gear through their heart
* pnkscrooge was kicked by &manishearth: eeew

and Scrooge was unkind to his comrades as well

<pnkscrooge> Crichit! Cargo is broken!
<acrichto> Are you talking to me?

The Why of Scrooge

<pnkscrooge> why invest in adding feature after feature?
<pnkscrooge> forcing people to learn new idioms
<pnkscrooge> they'll just leave and learn Java or C++ instead
<pnkscrooge> change is *death*
* pnkscrooge was kicked by &manishearth: off-topic philosophizing

Boo boo

After Crichit Crichton had gone home, Scrooge pondered over the borrowck error on his screen.

Boo boo

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
10 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error: aborting due to 6 previous errors

Scrooge decided he needed a larger screen to get perspective

Booooooo

 --> errmsg.rs:5:9
  |
5 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
  |         ^
  |
  = note: #[warn(unused_assignments)] on by default

warning: value assigned to `x` is never read
 --> errmsg.rs:6:9
  |
6 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
  |         ^

warning: value assigned to `x` is never read
 --> errmsg.rs:7:9
  |
7 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
  |         ^

warning: value assigned to `x` is never read
 --> errmsg.rs:8:9
  |
8 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
  |         ^

warning: value assigned to `x` is never read
 --> errmsg.rs:9:9
  |
9 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
  |         ^

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
5  |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
...
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
6  |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
...
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
7  |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
...
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
8  |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
...
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
9  |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
10 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error[E0597]: `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` does not live long enough
  --> errmsg.rs:11:5
   |
10 |         x = &yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss;
   |              ---------------------------------------------------------------------------------------------------------------------------------------------------------- borrow occurs here
11 |     }
   |     ^ `yyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss` dropped here while still borrowed
12 |     println!("x: {}", x);
13 | }
   | - borrowed value needs to live until here

error: aborting due to 6 previous errors

Boooooo!

ssyyyhhhhhhhhhhyyyhhhhhddhhhdddddddhhhdddddddddddddhhhhdddddddddddmmmmddmmmmdddddddddddddddddddddddddmmdddddddmmdddhhhyssooooooooooooosssssssyyyyyyyyyyyyyhhhhyys+:-````````````````````````````````````
yyyyhhhhhhhhhhhhhyyyyyhddhhhddddddddhhdddddddddddddddhddddddddddddmmmddddmmddddddddddddddhhhhhhddddddddddddddmmmddhhyyssooooo++++++ooooosssssssyyyyyyyyyyyyyyyyyso/-.```````````````````````````````````
yyhhhhhhhhhhhhhhhyyyyyhddhhhdddhddddddddddddddddddddddddddmdddhhddddddddddddddddddddddhhhhhhhhhhhhdddddddddddddddhyyssoo++++++++++++++ooooooosssssssssssssyyyyyyyo+:..``````````````````````````````````
hhhhhddhhhhhhdhhhyyyyyhhhhhdddhhhdddddddddddddddddddddddddddddhhhdddddddddddddddddddhhhhhhhhhyhhhhhdddddddddddhhhyssso++++++++++++++++++++++ooossssoooooosssyyyyyso/-.``````````````````````````````````
yhhhdddddddddhhyyyyyyyyhhhhddddhddddmddddddddddddddddddddddddddhddddddddddddddddhhhhhhyyyyyyyyyyyhhhdddddhhhhyyyssooo++++++++++/++++++++++++++ooooo++++++oosssyyyyo/:.``````````````````````````````````
yyhhddddddddddhyyyyyyyyhhhddmmdddddmmddddddddddddddddddddddddddhhdddddddddddhhhhhyyyyyssssssssssyyyhhhhhhhyyysssoo++++++++++/////////+++++++++++++////////++ooosyso+:-``````````````````````````````````
yyyhhddddddmddhyyyyyyyyhhdddmmmdddddmddddddddddddddddddddddddddhhhddddddhhhhhhhyyyyyssssoosssssssssyyyyyyysssooo+++++++++++//////////////////////////////////+++oso+/-.`````````````````````````````````
ssyyhhdddddmmddhyyyyyyhhdddmmmmmmdddddddddddddddddddddddddddddhhhhhhhhhhhhhhhhyyyyssssooooooooooooooosssssoooo++++/////++++//////////////////////////////::::/:/++++/-.`````````````````````````````````
ssssyyhhhddddddhyyyyyyhhddddmmmmddddddmdddddddddddddddhdddhhhhhhhhhhhhhhyyhhhyyysssssooooooooooo++++++ooo+++++++++//////++++/////////////////////////////::::::::/+++:...```````````````````````````````
yysssyyhhhhddddhyyyyyyyhdddddmmmddddddmddddddddddddddhhhhhhhhhhhhhhhhyyyyyyyyyyssoooooooooooooo++++++++++++/+++++++//++++///////////////////////////////::::::::::/++:-..`````````...```````````````````
yyyssyyyyyhhdddhhyyyyyyhhddddddddddddddddhhddddddddddhhhhhhhhhyyyyyyyyyyysssssssoooooooooooooo+++++++++++++////+/+++++++++/////////////////////////////////:::::::://:-..```````````````````````````````
yyyssyyyyyhhddhhhyyyyyhhhdddddddddddmddddhhdddddddddhhhhhhhyyyyyyyyyysssssssooooooooooooooooo++++++++++++++///////++++++++/////////////////////////////////::::::::::::-..``````.```````````````````````
yssssyyysyhhhhyhhhhyyyhhdddddddddddddddddhhdddddddddhhhhhyyyyysssssssssssoooooooooooooooooooo++++++++++++++/////++++/+++++////////////////////////////////:::::::::::::-..``````.....```````````````````
sssssyyyssyhhyyyhhhhhhhhhhdddddddddddddddddddddddddhhhhhyyyyysssssssssooooooooooooooooooooooo+++++++++++++++++++++++/+++++///////////////////////////////::::::::::::::-.``````````..```......``````````
ssssssyyyyyyyyyyyyhhhhhyhhhhddddddddddddddddddddddhhhhhhyyyyssssssssooooooooooooo++oooooooooo++++++++++++++++++++++++++++/////////////////////////////////::::::::::::--.`````````...........```````````
sssssssyyyyyyyyysyyhhhhyyhhhddddddddddddddddddddddhhhhhyyyyysssssssooooooooooooooooooooooooooo++++++++++++++++++++++++++////////////////////////////////////:::::::::::-.````..```..````.```````````````
ssssssssyyyssyyyssyyyhhyyhhdddddddddddddddddddddddhhhhyyyyysssssssoooooooooooooooooooooo+ooo+++++++++++++++++++++++++///////////////////////////////////////:::::::::::-..```..`````````````````````````
ssssssosyyysssssssssyyyyhhddddddddddhhddddddddddddhhhhyyyysssssssooooooooooooooooooo+o++++++++++++++++++++++++/+//////////////////////////////////////////////:::::::::--..``..`````````````````````````
ssssssssyyssssssssyyyyyyyhddhhddddddhhdddddddddddddhhhyyyysssssssooooooooooooooooooo+oo++ooooo++++++++++++++++/////////////////////////////////////////////////////:::::---..```````````````...`````````
ssssssssssssssssssyyyyyyyhdhhhddmmdddddddddddddddddhhhhyyyysssssssooooooooooooooooooooooooooooo+++++++++++++++/////////////////////////////////////+////////+++++///////::--..``..```..`````...`````````
oosssssssssssoosssyyyyyyyhhhhhdmmddddddddddddddddddhhhhyyyyssssssssooooooooooooooooooooooo++ooo++++++++++++++//////////////////////////////////+++++++++++++oooooo++++/////:-..`.``...........``````````
+osyyyssssssssssssyyyyyyyhhhhhddddhhdddddddddddddddhhhhyyyssssssssssoooooooooooooooooooooo+++o+++++++++++++++++/++++++//////////+++++++++++++++++++++ooooooossyyyssssooo++++/:-..`....``.......`````````
oosyyysssooosssssssysssyyhhhhhhhhhhddddddddddddddddhhhhyyyssssssoooooooooooooooooooooooooooooo++++++++++++++++++++++++++++++++++++++++++++++++++oooosssssssyyhhhhhhhyyyyyssooo+:.......`````....```...``
oosyyssooooossssossysssyhhhhhhhhhhhddddddddddddddddhhhhyysssssssooooooooooooooooooooooooo+++++++++++++++++++++++++++++++++++++++oooooooooooooooosssyyyyyyyhhhddddhhhdhhhhhyyyyo/-..``....```..``````.```
ooossssooossssssossyssyyhhhhdhhyyyhhhddddddddddddddhhhyyysssssssoooosoooooooooooooooo++++++++++++++++++++++++++++oooo++++ooooooooooooooooooooooossyyyhhhhhddddddddddddddhhhyyys+/:-..-----..-......```..
ooossssooosyysssssssyyyhhhhhhhyyyyyhhhddddddddddddhhhhyyyssssssooooooooooooooooooo+++++++++++++++++++++oooooooosssssssoooossssssssssssssssoooooossyyhhhhdddddddddddhhhhhyyyyyyssoo+++++++ooo+++/:--.``..
oooosssoosyyyysssssyyyyhhyyyyyysyyyhhhhddddddddddhhhhyyssssssooooooooooo+oooooooo++++++ooooo+++++++oooooossssyyyyhhyyyyssssyyyyyyyssssssssssoooossyyhhhhddddddhhhhhyyyyyyysssyyyyyyhhhhyhhhdddhhso/-.```
oooooooossyyyyyyyyyyyyyhhyyyyyssyhhhhhhddddddddddhhyyysssssooooooooo+++++++++o+oooooooooooooooooooosssyyyhhhhhddddddddhhhyyhhhhhyyyssssssssssssosssyhhhhhhhhhhhhhhhhhhyyyyysssssyyyyyhyyyyyhdmmdhy+:.``.
+++oo++osyyyyyyyyyhyysyyhhyyysssyyhhhhdddddddddhhhyyysssoooooooooo+++////++++++ooooooooooooosssyyyyyhhhddddmmmddddddddddhhhhhhhhhyyssssssssooooossyhhhddddhhddhhhhhhhhyyhhysssssyyhhhhhhyssydmmdhyo:.`..
+++ooooossssyyyyhhhhyyyyyyyssssyyhhhyhdddddddhhhhyysssooooooo++++++//////+++oooooosssssssssyyyhhhhhddddddmmmdddddmmdddddddhhhhhyyyssssoooooooooosyyhdddddddddddhhyyyyyhhhhhysso+++ooossssssydmmmhy+:.``.
ooooooossssssyyhhhhhyyyyyyssossyhhhhhhddddddhhhyyysssoooo++++++++///::///++ooooossyyyyyhhhyhhhhddddddddddddddddddddddddddddhhhhyyysssooooooo++osyhhddddddddddddhyssossyhhdhyso/:-----:/ooosydmmdyo:-....
sso++oosssssyyyhhhhyyyyyyssoosyyhhhhhdddmdddhyyysssooo++++++++/////::://++oosssyyyhhhhhhhhhhhddddhhhhdddddddddhhhhhhhhhdddddhhhhhyysssooo++++ooyhhdddddddddhhhhyyso++osyhhhyo/:-....`.-+oooyddhs/-......
ssoooooosssyysyyhhhhhhhhyyssssyhhhhhhddddddhhyyssooo++++++++++//::::://++ossyyyhhdddddddddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhdddddddddhyyssoooooosyhhdddddddddddhhhhyyo++osyyyso+/--......:+oooydho:......``
oosssoooossssssyyhhhhhhhhyyyyyhhdddhhddddhhhyyssoo++++++++++++/::://///+osyyhhhdddhhhhhhhhhhhyyhhhhhhhhhhhhhhhddddhhhhhhhhhhhhhddddddhhhhhhhhhdddddddddddddhhhhhyyssssyyyso+/:-.......:+ooosys/.`.......
ssssssooossssssyyhhhhhhhhhhhhhdddddhhhddhhhyyysoo+++++++++++//:::////++osyyhhhhhhhhhhhhhhhhhhhhhhdddddhhyyyyyhhdddhhhhyyyyyyyyhhddddddmmmmmmddddddddhhhhhhhhyyyyyysssssssoo+/:-......-/+ossso+:.`..``...
yyysssssssssyyyyyyhhyyyhhhhhhhhhhhhhyhhhhyyyssoo++///////////////+++oossssyyyhyyyhhhhhdddddddddddddddhhhysssssyyhhhhhhyyyyyyyyhhhddddddmmmddhyyyyhddhhyyyyyyyyssssssssooooo+/:-....-:///+syo/:-.`.`.....
yyyssssssyyhhyysoooooooooooooooosssooossoooo+++///::////++++oooosssssyyysssyyhhdddddddddddddddddddddhhyyysooosssyyyyyyyyyyyyyyyhhhddddddhhysoo+++oshhhyssyyyyyyssssssssoooo+/::--..-:///+syo:..........`
yyyssyyyyyhhhso+/:::::::::::--:::::::::::::://///////++oossssyyhhhhhhhhhyyyyhddddmmmddddddddddddddddddhhys+oossyyyyyyyysssssyyhhhhdddddhysooo++//++oyyyssyyyyyyyysssssssoo++//:-...-:/+osyys/::----.....
sso+++ooossssoooooooo++++++++++++++//////////+++++++ooossyyyyhhddddhhhhhhyyhhddmmmmmmdddddddddddddddddhhysossyyyyyyyyyssssssyyyhhhhddddhysooo+++///++osssssssssssssooooooo+++/:---:/+osyyyssoo++++//////
///////+++oooossyhhhhhhhhhyhhhhhhhyyyyysssssssssssssssyyyyhhhhdddddddhhhhhhhhddmmmmmmmddddddddddddddhhhyyyyyyyyyyyyyyysssssssyyhhhhddddhyssoo++++////++oooooooooooooo++++oooo+++++ossyyyysssssssssoooooo
-::/++oooooooooosyhhddddddddmmmdddddddddddhhhyyyyssssyyyyyyhhhhhhddddddhhhhhhddmmmmmmddddhhhhhhhhhhhhyyyyyyyyyyyyyyyyysssssssyhhhhddddhysssoo+++++//////+oooooooooooooooooooosssssssyyssssssyssssssoosss
//+oossssssssooossyyhhddddddmmmmddddddddddhhhyssooooooooooosssssyyhhddhhhhhhdddmmmmmmddhhhhhhhhyyyyyyysssssssssyyyyysssssssssyyhhhdddhyysssoo+++++//////+oosssssssssyyyyssssso++//+osyyssssyyyysssssssss
oossyyyyyyyyyysssssyyhhhdddddmmmdddddddddhhhhysoo+++++++ooooooossyyyhhhhhhhhhhhddddmdhhhhhyyyyyyyyyysssssssyyyyyyysssssssssssyhhhhhhhysssssoooo++++//////+oossssssssssooooo+++//::/+oyyssssyyyyyssssssss
ssyyyyyyyyyyyyyyyyyyyyyhhhdddddddddddddddhhhyysoo++++++++ooooooossyyyyyyyyhhhhhhhhhddhhhhhhyyyyyyyyyyyyyyyssysssssssssssoosssyhhhhhhyysssssoooo+++++///////+ooooooo+++++++//////:::/ossssssyyyyyssssssss
syyyyysssssssyyyhhyyyyyyhhhddddddmdddddddhhhyssoo+++++++++oo+++oossyyyyyyyyyyyyyyyyhhdhhyyyyyyyyyyyyyyyyyssssssoooooooossssyyyhhhhyyysssoooooooo+++++/////:///+++++++///++///////::/+osssssyyyyyssssssss
ssyyysssooooossyyyyyyyyyyhhhhhhddmmmdddddhhyyssoo+++++++++++++++osssyyyyyyyyyyysssssyhdhyyyyyyyyyyysssssssssssssssssssssyyyyhhyyyyssssoooooooooooo+++++///////////+++/////////////:/+oosssssyyyyysssssss
ssyyyssooo+oooossyyyyyyyyhhhhhhhddmmddddhhhyyssoo+++++++++++++++oosssyssssssyssssssssyhhhhyyysssssssssssssssssssyyyyyhhhhhhhyyyssssooooooooooooooo++++++//////////++++////////////://+osysssyyyyysssssss
ssyyysooooooooossyyhhhhhhhhhhhyhhdddddddhhyyysooo+++++++++++++++ooossssssssssssssssssyyhddhhhhyyyyyyyyyyyyyyyhhhhyyyyyyyyyyyyssssssooooooooooooooo++++++////:::////++////////////:::/+osyyssyyyyyyssssss
ssyyysooooooosssyyhhhhhhhhhhhyyyyhhddddddhhyysooo+++++++++++oooooooosssssssssssssssssssyyhyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssoosossooooooooooo++++++/////:://////////////////:::/oyyyssyyyyyyysssss
ssyyysooooooosssyhhhdddhhhhhhyyyyyhhdmmmddhyyssooo+++++++++oooooooooossssssssssssssssssssssssssssssssssssssooooooooooooooooooossssssssssssoooooooooo+++++++////////////////////////::/oyhyssyyyyyyysssss
ssyyysooooooosssyyyhhhhhhhhhhyyyyyyhddmmmddhyyssoooo+++++++oooooooooooooossssssssssssssooooooooooooooooooooooooooooooooooooooossssssssssssooooooooooo+++++++/////::://++++/////////::/oyhyssyyyyyyyyssss
ssyyysooooooosssyyyyhhhhhhhyyyyyyyyyhddmmddhhhysssooo++++++oooooo++++ooooossssoooooooooooooooooooooooooooooo++++ooooooooooooooossssyssssssssoooooooooo++++++//////:::/+++++//++///////oyhyssyyyyyyysssss
ssyyyysooooooossyysyyyhhhhyyysyyyyyyhhdmmdddhhhyyssooo+oooooooooo++++++ooooooooooooooooooooooooooooo++++++++++++++++++oooooooosssssysssssssoooooooooooo++++++/////:::://++++++++++////oyhyysyyyyyyyyssss
sssyyyysooooooosssssyyhhhyyssssyyyyyyhddmddddhhhyyssooooooooooooo++++++oooooooooooooooo+++++oooo+++++++++++++++++++++ooooooossssssssssssssoooooooooooooo+++++///////::::/++oo+++o+++//oyhyyyyyyyyyyyssss
hhyssyyssooooossssssyyhhhhyysssyyyyyyhddddddddhhhyyssooooooooooooo+++++ooooooooooooo++++++++++++++++++++++++++++++++oooooosssyyysssooooooooooooooooooooo++++/////////:::/+ooo+++ooo+++oyhhyyssyyyyyyysss
ddhsssyyssoooooooossyyhhdhhysssyyyyyyyhddddddddhhyyyssooooooooooooooooooooooooooooooo+++++++++++++++++++++++++++++ooooooossyyyyssoooooooooooooooooooooooo++++///////////++ooo++++ooo++syhhyyssyyyyyyysss
mmdhyysyyysoooooosssyyhdddhyssssyyyyyyhhddddddhhhyyyssssoooooooooooooooooooooooooooooo+++++++++++++++++++++++++ooooooooossyyyyysooooooooooooooooooooooooooo++++++++////+++oooooo+++++osyhhyyyssyyyyyysss
mmmmdhysysssoooooossyyhhhhhyysssyyyyyyyyhhhhhhhhyyyyssssssooooooooooooooooooooooooooooo+++++++++++++++++++ooooooooooooosssyhhyyssooooooooooossssssssssssssoooo++oo+++++++++oooooo++++osyhhyyyssyyyyyysss
NNNNmdhyssssssooooossyyyyyyyyyyhhyyyyyyyyyyyyyyyyysssssssssssoooooooooooooooooooooooooooooooooooooo+oooooooooooooooossssssyhhhyyysssssssosssssyyyyyyyyyyyssssoooooo+++/++++++++ooo++osyyhhyyyyysyyyyssss
NNNNNmdhysssssssooooossssssyyhhdhhhhyyyyyyyyyyyyyyssssssssssssooooooooooooooooooooooooooooooooooooooooooooooooooosssssossssyyyyyyyyyyyyyyyyyyyyyhhhhhhhhyyyyssssooo+++//////+++ooo++osyyhhyyyyyyyyyyssss
mmNNNNmmdyysssssssoosssssooossyhhhhhhhyyyyyyyyyyyysssssssssssssssooosssssssoooooooooooooooooooooooooooooooooooosssssssoossssyyyyyyyyyyhhhyyyyyyhhhhhhhhhhyyyysssooo++//////++++oo++oosyhhyyyyyysyyysssss
mmmNNNNmmdhyssoooooosssssooooossyyyyyhyyyyyyyyyyyyyysssssssssssssssssssssssssssssssooooooooooooooooooosososssssssssossosssssssssssyyyyyyyyyyyyyyyyhhhhhyyyyssssoooo++++///+++++++++osyyyyyyyyyyyyyysssss
mmNNNNNNmmdhyssoooooossssooooooosssyyyyhyyyhyyyyyyyyysssssssssssssssssssssssssssssssssssoooooooooososssyyyyysssssssssssssssssssssssssssssssssssssssssssssssssssyyssssoo+++++++++oooosyyyyyyyhyyyyyysssss
mmNNNNNNmmdhyyyssoooooooooooooooossssyyyyyhhyyyyyyyyyysssssssssssssssssssssyssssssssssssooooossssssososyyyyysssssssssssssssssssssssssssssssssssssssssssssoossssssssssoooo+++++//ooossyyyyyyyhhyyyyysssss
mmmNNNNNmmdhhyyyssssoooooooooooooooossyyyhhyhhhhyyyyyyyssssssssssssssssssyyyyysssssssssssooossssssssssyyyyyyssssssssssssssssssssssssssssssssssssssssssssssoooossssssooooo++++///ooosssyyyyyyhhhyyyssssss
mmmmNNNNmmdhhyyyyyyyyssoooooooooooooossyyhhhhhhhyyyyyyyyssssssssssssssssyyyyyyysssssssssssssssssssssssyyyyyssssssssssssssssssssssssssssssssssssssssssssssoooooooooooooooo++++///+oosssyyyyyyyhhhyyssssss
mmmmmNNNNmddhyyyyhhhhhysssoooooooooooossyhhhhhhhhyyyyyyyyysssssssssssysyyyyyyyyysssssssssssssyysssssssyyyyssssssssssssssssssssssssssssssssssssssssssooooooooooooooooooooo++++///+ossssyyyyyyyhhhyyssssss
mmmmmmNNNNmdhyyyyyhhdddhyysssooooooooossyhdddhhhhhyyyyyyyyysyysssssyyyysyyyyyyyyyyyysssssssssyyssssssssysssssssssssssssssssssssssssssssssssssssssssssssoooooooooooooooooo++++///osssssyyyyyyyhhhhyssssss
ddddmmmNNNmdhhyyyyyhdmmmddhyyysssssssssyhdddddhhhhhyyyyyyyyyyyysyyyyyyyyyyyyyyyyyyyyssssssssyysssssssssssssssssssssssssssssssssssyyyysssssysssssssssssssssoooooooooooooo++++////sssssssyyyyyyhhhhyysssss
dddddmmNNNmmdhyyyssydmNNNmmddhhyyyyyyyhhhdddddhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssyyyssssssssssssosssssssssssssssssssyyyyhyysssssyssooosssssoooooosssssoooooooo+++/////ssssssssyyyyyhhhhyysssss
hddddmmmNNmmddhyyysyhmmNNNNmmddddhhhhhhhdddddddhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssyyyssssssssssosssssssssssssssyyyyyyyyyyhhyssoossso+++oooo+++++++++++++ossssooo++/////yyssssssyyyyyhhhhhyysssy
hhhdddmmNNNmmdhhyysyhdmNNNNNmmmdddddddddddddddddhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssyyysssssssssssssssysssssyyyyhhhhhhhyyyyhyyssoosso++++oooo++////++++///++osssso+++////yyssssssyyyyyhhhhhyyssss
hhhdddmmmNNNmmdhhysyyhdNNNNNNmmdddhddddhhhhhhhdhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssyyyyysssssssssssssyyyyyyyyhhhhhhhhhhyyyyyyyyysssssoooossssoo++++++++/////++ooooo++////yysssssssyyyyhhhhhyyssss
dddddddmmmNNmmddhyyyyhdmNNNNNmmmddhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssyyyyyyyhhhhhhhyyyyyyyyyyyyyyyyyyyyssyyysssssssssooo++////++osoo++///yysssssssyyyyhhhhhhyssss
dddddddmmmNNNmmdhhhyyyhdmNNNNNmmdddhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyysssoossssssssyyyyyyyyyyyssssssssssssssssssssssssssssyysssssssssoo++//+ossso++//yysssssssyyyyhhhhhhyssss
mmddddddmmmNNNmddhhhyyhdmNNMNNNmmddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyysssssssssssssssssssssssssssssssssoooooooooooooooooooooooooossssooo++ossssso+++syssssssssyyyhhhhhhyssss
mmddhhdddmmmNNmmddhhyyhhdmNNNNNmmdddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssooooooooooooooooo+++ooooo+oooooooossssso+++ssssssssssyyyhhhhhhyysss
mmdhhhhddmmmmNNmmddhhhhhdmNNNNNNmmddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssoooooooooooooo++++ooo+++++++++oooooooo+++osssssssssyyyyhhhhhyysss
mmdhhhhhdddmmNNNNmmddhhhhdmNNNNNmmddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssoooosssssssssssssssssssoooooooooossooooooooooo++++++++++++++++++oossssssssyyyyhhhhhyysss
mmddhhhhdddmmmNNNNmmddhhhddmNNNNmmdddhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssososssssssssssssssssssoossssssssssoooooooooo+++++++++/+///+++ossyyssssyyyyyhhhhyysss
mmddhhhhhdddmmmNNNNNmdhhhhhdmNNNmmmdddhhhhhhhhhhhhhhhhhdddhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssssssssssssssssssssssssooooo++++++/////++ossyyysssyyyyyhhhhyysss
mmddddhhhhddmmmNNNNNmddhhhhdmmdddmmddddhhhhhhhhhhhhhhhhhdddhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssssssssssssoossssyyyysssoo+++++++///++/+ossyyysssyyyyyhhhhyysss
dddmmdhhhhdddmmNNNNNmmdhhhhdddysydmmdddhhhhhhhhhhhhhhhhhhhddddhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssssssssssssssssyyyyyyssoo++++++//++++++ossyyysssyyyyyhhhhyysss
dddmmmddddddmmmNNNNNNNmdhhhhhhoosdmmddddhhhhhhhhhhhhhhhhhhdddddddhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssssssssssssssyyhhhyysso++++++//+++oooooossssysssyyyyyhhhyysss
hhdmmmmmddddmmmmNNNNNNmmdhhhhy+/ohmmdddddhhhhhhhhhhhhhhhhhhddddddddhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyysssssssssssssssssssssssssssssssssssssssssosssyyhhhhhyso++++++//+++ooooossssssyssyyyyhhhhyysss
hhddmmmmmdddmmmmNNNNNNNmddhhhy+/ohmmdddddhhhhhhhhhhhhhhhhhhhdddddddddhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssssssssssssssssosssyyhhhhyyso+++++//++oooooooosssyyysssyyyhhhhyssss
hhhddmmmmddmmmmmmNNNNNNmddhhhy+/oydmmmdddhhhhhhhhhhhhhhhhhhhhdddddddddddhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyysssssssssssssssssssssssssssssssssoosssssssssyyyyssooo+++////+oossssoooossssssssyyyyhhhyysss
hhhhdmmmmmmmmmmmmNNNNNNmmddddho+oyhdmmdddhhhhhhhhhhhhhhhhhhhhhhddddddddddddhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyysssssssssssssssssssssssssssssoooooooooooooooooooo++++++++//+ossyyyssssoooooosssyyyhhhyysss
hhhhddmmmmmmmmmmmNNNNNNNmdddmhsooshdddddddhhhhhhhhhhhyyyhhhhhhhhhddddddddddddhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyssssssssssssssssssssssssssoooooooooo+++++++++++++++++++///+ossyyyyyyssooooooosssssssssss
hhhhhdmmmmmmmmmmmmNNNNNNmmddmdysosyhddddddhhhhhhhhhhyyyyyyyyyhhhhhhddddddddddddddhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyysssssssssssssssssssssoooooooooo+++++++++++++++++++///+ossyyyyyyyyyssoooooooooooooooo
hhhhhdmmNNmmmmmmmmmNNNNNNmddddyssoshddddddhhhhhhhhhyyyyyyyyyyyyhhhhhhhddddddddddddddhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyyyysssssssssssssssssooooooooo++++++++++++++++++++//++syyyyyyyssyyyyysssssssoooo+ooo
ddhhdddmNNmmmmmmmmmmNNNNmmdddhhysoshddddddhhhhhhhhyyyyyyyyyyyyyyyhhhhhhhddddddddddddddhhhhhhhhhhhhhhhhyyyyyyhhyyyyyyyyyyyysssssssssssssssooooooooo++++++++++++++++++++++++syhhhhyyyssssyyyyyyssssssssooo
dddddddmNNmmmmmmmmmmNNNNmddhhhhhysshddddddhhhhhhhhyyyyyyyyyyyyyyyyyyhhhhhhhddddddddddddddddddhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyssssssssssssooooooooooo+++++oo++++++o+++++++oshhhhhhyyyyyssyyhhyyyyyyyyysoo
ddddddmmNNmmmmmmmmmmNNNmmdhhhdddhyyhddddddhhhhhhhhyyyyyyyyysssssyyyyyyyhhhhhhdddddddddddddddddddhhhhhhhhhhhhhhhhhhhhyyyyyyyyyysssssssssssoooooooooooo++++ooo+++++o++ooooosyhhhhhhhhhyyyssyyyyyyyyyyyysoo
ddddddmmmNmmmmmmmmmmNNNmmdhhddddhyyhddddddhhhhhhhhyyyyyyyysssssssssyyyyyyyyhhhhhhddddddddddddddddddddhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyysssssssssoooooooooooooooooooooooooossyyhhhhhhhhhhyyyyyyyyyhhhhyyysoo
ddddddmmmNmmmmmmmmmmmNmmdhhhddddhyyhddddddhhhhhhhyyyyyyyyssssssssssssssyyyyyyyyhhhhhhhddddddddddddddddddddhhhhhhhhhhhhhhhhhhhhyyyyyyyyyssssssssooosooooooooooooooooooossyyyyyhhhhhhhhhhhyyyyyyyhhhhyssoo
ddddddmmmNmmmmmmmmmmmmmmddhhdddhhyyhdddddhhhhhhhhyyyyyyyysssssssssssssssssyyyyyyyhhhhhhhhhhhhhhhdddddddddddddddhdhhhhhhhhhhhhhhhhhyyyyyyyyyssssssssssssssssssssssssssssyyyssyyhhhhhhhhhhhhyyyyyhhhhysooo
mmmdddmmmmmmmmdddddmmmmmmdhhhhhhhyhhdddddhhhhhhhhyyyyyyyyssssssssssssssssssssssyyyyyyyhhhhhhhhhhhhdddddddddddddddddddhhhhhhhhhhhhhhhhhhyyyyyyyyysssssssssssyyssssssyyyyyyyyyyyyyhhhdddhhhhhyyyyyhhyssooo
mmmddddmmmmmmddddddddmmmddhhhhhhhhhdddddhhhhhhhhhyyyyyyyyssssssssssssssssssssssssssyyyyyyyhhhhhhhhhhdddddddddddddddddddddddhhhhhhhhhhhhhhhhhhyyyyyyyyyyyyyyyyyyyssssyyyyyyyyyyyyyyhhhdddddhhhyyyyyysooss
mmmddddmmmmmmddhhddddmmmddhhhhhhhhhdddddhhhhhhhyyyyyyyyyysssssssssssssssssssssssssssssyyyyyyyhhhhhhhhhhhhhhhhhhhhhhhhhhhdhhhhhhhhhhhhhhhhhhyyyyhhhyyyyyyyyyyyyyysssssssyyyyhhyyyyyyyhhddddddhhyyyyysssss
mmmdddddmmmmmdhhhhddddmdddhhhhhhhhhdddddhhhhhhhyyyyyyyyyyssssssssssssssssssssssssssssssssyyyyyyyyyyhhhhhhhhhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyssssssyyyyyyyyyyyyyyyyyyyyyssssyyyyyhhhhyyyhhhddddddhhhyyysssss
mmmdddddmmmmdhhhhhhdddddddhhhhhhhhhdddddhhhhhhyyyyyyyyyyysssssssssssssssssoooooosoosssssssssssyyyyyyyyhhhhhhhhhhhhhhhhhhhhyyyyyyyyyyyssssoooooosyyyyyyyyyyyyyyyyyyyyyyysssssyhhhhhhhhyhhhhddddddhyssyyss

Tonight You Will Be Visited

<pnkscrooge> its the ghost of nmatsakis!
<nmatsakis> the chains of stability and backwards compat are heavy!
<nmatsakis> you must change your way of thinking
<nmatsakis> tonight you will be visited by three spirits

Footnote

Niko is not dead

(Well, maybe he is in this story)

(Or at least overwhelmed)

What's going on in this talk?

Tonight

You will be visited by Three Spirits

  • The Ghost of Epochs Past
    Changes running up to 1.0
  • The Ghost of Epochs Present, and
    Changes since 1.0 up to now
  • The Ghost of Epochs Yet To Come
    Changes anticipated for future releases

The First of the Three Spirits

IRC

<epochspast> I am the Ghost of Epochs Past
<pnkscrooge> Long past?
<epochspast> No. Rust's past.
<pnkscrooge> What business brought you here?
<epochspast> Rust's welfare!

The run-up to 1.0

Rust 1.0 alpha 9 January 2015
six weeks later Rust 1.0 alpha.2 20 February 2015
six weeks later Rust 1.0 beta 3 April 2015
six weeks later Rust 1.0 15 May 2015

What big changes happened back then?

1.0 alpha: the int-pocalypse

(RFC 544)

Once had int and uint. It was confusing.

Many renaming initiatives (rust-lang/rust#9940 in 2013, RFC 464 in 2014); all met with resistance

Team almost launched 1.0 with int/uint.

Core team learned important lessons about community input and interaction.

After considering many options {imem/umem, offset/size, intp/uintp, ...} finally settled on isize/usize we have today.

1.0.0-alpha.2: Drop Check

(RFC 769)

Rust used to not allow this:

pub struct A<'a, X>(&'a i32, X);
impl<'a, X> Drop for A<'a, X> {
    fn drop(&mut self) { println!("dropping A"); }
}

(rustc did not know/require the &'a i32 be valid while destructor was running)

dropck rules fixed that, ...

... and, yes, caused some code to start being rejected.

<epochspast> You were once willing to accept breakage
<pnkscrooge> "I was young and foolish then; ...
<pnkscrooge> ... I feel old and foolish now."

Footnote on Drop Check

The full and true history is probably a 45 minute talk in itself.

1.0 beta: catch_panic

(PR 23651)

Was not possible to recover from a panic on the thread that caused it. (Forced monitor/worker split in separate threads, due to the API's in place.)

Initially landed as catch_panic in rust-lang/rust/pull/23651.

Later renamed to panic::recover as part of RFC 1236; but today we know it as ...

panic::catch_unwind

it was finally stabilized in 1.9 release (May 2016); much discussion on rust-lang/rust#27719

1.0: mem::forget is safe

(RFC 1066)

Represented firming up of collective thinking about what unsafe is meant for.

IRC

<epochspast> You see? Rust can change!
<pnkscrooge> That was all madness running up to 1.0.
<pnkscrooge> It proves nothing about where we are now.

The Second of the Three Spirits

IRC snippets

<epochspresent> I am the Ghost of Epochs Present
<pnkscrooge> Spirit, conduct me where you will
<pnkscrooge> I went forth last night on compulsion,
<pnkscrooge> and I learnt a lesson which is working now.
<pnkscrooge> if you have aught to teach me, let me profit by it.

What are changes that mattered for Rust today

Poll

Compared to 1.0

  • some things falling outside lang/libs

IDE support, rustup, nicer diagnostics (noted by many)

  • some features in Rust nightly channel today

never_type: match x: Result<T, Void> { Ok(_) => ... }

  • some features in Rust beta channel today

Rc<str> (RFC 1845)

  • some features in stable Rust today

if let, ?-syntax, pub(crate), impl Trait

macros 1.1 / Custom Derive / Serde (noted by many)

Procedural macros, custom #[derive]

Lets hack some code

/// Measure number of heap-allocated values owned by self.
trait Weight {
    // default: most values laid inline, not separate `malloc`'ed
    fn weight(&self) -> isize { 0 }
}

Some base cases:

impl Weight for i32 { }
impl Weight for i64 { }
// (et cetera)

impl<'a, T: ?Sized> Weight for &'a T { }     // someone else owns `T`
impl<'a, T: ?Sized> Weight for &'a mut T { } // not us
// (`?Sized` marker allows things like `str` or `[i32]` as the `T`.)

The first interesting cases

Heap-allocated things like String and Box must be accounted for.

impl Weight for String {
    fn weight(&self) -> isize { 1 } // just a single heap allocation
}

Box has a heap allocation ...

plus its contents may own others! 

impl<T: Weight> Weight for Box<T> {
    fn weight(&self) -> isize { 1 + (**self).weight() }
}

#[test]
fn test_box_chain() {
    assert_eq!( Box::new(Box::new(Box::new("hi"))).weight(), 3 );
}

Over Weight Demo

pub fn breakfast() {
    let f = FrenchToast;
    assert_eq!(f.weight(), 0);
    let p1 = Pancakes { topping: "syrup", atop: None };

Pop quiz: what's p1.weight()?

    assert_eq!(p1.weight(), 0);
    let p3 = Pancakes {
        topping: "butter",
        atop: Some(Box::new(
            Pancakes { topping: "berries",
                       atop: Some(Box::new(
                           Pancakes { topping: "syrup",
                                      atop: None })) }))};

How about p3.weight()?

    assert_eq!(p3.weight(), 2);

("just count the boxes!")

}

Well...

I just lied to you. Code like

    let p1 = Pancakes { topping: "syrup", atop: None };
    p1.weight()

doesn't work yet; why not?

Likewise, Option<Box<T>> won't work either.

But we want it to work, like this:

#[test]
fn test_option_box() {
    let s: Option<Box<i32>> = Some(Box::new(10));
    assert_eq!( s.weight(), 1 );

    let n: Option<Box<i32>> = None;
    assert_eq!( n.weight(), 0 );
}

("just count the boxes")

The first annoying cases

impl<T: Weight> Weight for Option<T> {
    fn weight(&self) -> isize {
        match *self {
            Some(ref t) => t.weight(),
            None => 0,
        }
    }
}

(bog standard recursion)

impl<T: Weight, E: Weight> Weight for Result<T, E> {
    fn weight(&self) -> isize {
        match *self {
            Ok(ref t) => t.weight(),
            Err(ref e) => e.weight(),
        }
    }
}

(yadda yadda yadda)

Implementations from previous slide were entirely mechanical, derived directly from structure of Option and Result types, respectively.

In fact, one might suggest that a program could generate them for us.

So lets do that

(working from the hypothesis that its easier to transcribe a type definition into a macro invocation...)

use weight_derive::impl_weight_for;
impl_weight_for!(enum Option<T> { Some(T), None });

expands to (after some human adjustment of whitespace):

impl<T> Weight for Option<T> where T: Weight, {
    fn weight (&self) -> isize { match *self {
        Some(ref x_0) => 0 + x_0.weight(), None => 0, } } }

(Okay, less readable than previous slide. But who cares, its a macro!)

What does the macro implementation look like?

You don't want to see it.

Since you asked

#![feature(proc_macro)]
extern crate proc_macro;
extern crate syn;
#[macro_use] extern crate quote;

use proc_macro::TokenStream;

#[proc_macro_derive(Weight)]
pub fn weight(input: TokenStream) -> TokenStream {
    let s = input.to_string();
    let ast = syn::parse_derive_input(&s).unwrap();
    let gen = impl_weight(&ast);
    gen.parse().unwrap()
}

#[proc_macro]
pub fn impl_weight_for(input: TokenStream) -> TokenStream {
    let s = input.to_string();
    let ast = syn::parse_derive_input(&s).unwrap();
    let gen = impl_weight(&ast);
    gen.parse().unwrap()
}

fn impl_weight(ast: &syn::DeriveInput) -> quote::Tokens {
    let name = &ast.ident;
    let weight_body = match ast.body {
        syn::Body::Struct(ref variant_data) =>
            generate_match_for_cases(
                ::std::iter::once((&ast.ident, variant_data))),
        syn::Body::Enum(ref variants) =>
            generate_match_for_cases(
                variants.iter().map(|v| &v.ident)
                    .zip(variants.iter().map(|v| &v.data)))
    };
    let (impl_params, ty_args, where_clause) = ast.generics.split_for_impl();
    let mut added_bounds: quote::Tokens = quote! { };
    for bound in ast.generics.ty_params.iter()
        .map(|ty_param| &ty_param.ident )
        .map(|ident| quote! { #ident: Weight, })
    {
        added_bounds = quote! { #added_bounds #bound };
    }
    return quote! {
        impl #impl_params Weight for #name #ty_args 
            where #where_clause #added_bounds {
                fn weight(&self) -> isize { #weight_body }
        }
    };
}
fn generate_match_for_cases<'a, I>(iter: I) -> quote::Tokens
    where I: Iterator<Item=(&'a syn::Ident, &'a syn::VariantData)>
{
    let mut arms = quote! { };
    for (variant_ident, variant_data) in iter {
        let (field_names, code) = generate_variant_code(variant_data);
        let arm = match *variant_data {
            syn::VariantData::Unit =>
                quote! { #variant_ident => #code },
            syn::VariantData::Struct(..) =>
                quote! { #variant_ident { #(ref #field_names),* } => #code },
            syn::VariantData::Tuple(..) =>
                quote! { #variant_ident(#(ref #field_names),*) => #code },
        };
        arms = quote! { #arms #arm, }
    }
    return quote! { match *self { #arms } };
}

fn generate_variant_code(vd: &syn::VariantData) -> (Vec<quote::Tokens>, quote::Tokens)
{
    let bind_names: Vec<_> = match *vd {
        syn::VariantData::Unit => vec![],
        syn::VariantData::Struct(ref fields) => fields.iter()
            .map(|f|f.ident.as_ref().unwrap()) // reuse names for struct fields
            .map(|i| quote!{ #i })
            .collect(),
        syn::VariantData::Tuple(ref fields) => fields.iter()
            .enumerate() // make fresh names for tuple fields
            .map(|(num, _)| { quote::Ident::new(format!("x_{}", num)) })
            .map(|i| quote!{ #i })
            .collect(),
    };
    let code = generate_sum_of_var_weights(&bind_names);
    (bind_names, code)
}

fn generate_sum_of_var_weights(names: &[quote::Tokens]) -> quote::Tokens {
    let mut body = quote! { 0 };
    for field_access in names {
        body = quote! { #body + #field_access .weight() };
    }
    return body;
}

(Told you so!)

Sad News

Procedural macros like impl_weight_for! are not yet available in the Rust stable channel...

... except for one special case: #[derive]!

Stable custom #[derive]

#[derive(Weight)] struct FrenchToast;

yields:

impl Weight for FrenchToast where {
    fn weight (&self) -> isize { match *self { FrenchToast => 0, }}}

and

#[derive(Weight)]
struct Pancakes {
    topping: &'static str, atop: Option<Box<Pancakes>>,
}

yields:

impl Weight for Pancakes where {
    fn weight (&self) -> isize {
        match *self {
            Pancakes { ref topping, ref atop } => 
                0 + topping.weight() + atop.weight(),
        }
    }
}

derive is the important special case

While it is painful to write out the implementations for standard library types like Option and Result, at least the author of a crate providing trait Weight has the option of doing that work.

But that is useless when it comes to supporting downstream crates of their clients.

That is why support for derive is so important: It enables crates to to provide a trait and then give clients a zero-cost way to get impl's on their own types.

Serde

By implementing Serde's Serialize and Deserialize traits (or using derive to do it automatically), data structures acquire the ability to serialize and deserialize themselves.

The serializaton works with many data formats: JSON, CBOR, YAML, TOML, Pickle (common in Python), BSON (used by MongoDB), URL, et cetera.

They do this via code generated at compile-time; no need for reflection nor runtime type introspection!

In many situations Serde serialization performs at same speed as a handwritten serializer.

Other crates

derive isn't special-cased around Serde; see also e.g. Deisel crate.

Insight

"Small" language additions can enable huge library/ecosystem wins

The Last of the Spirits

IRC

* epochsyettocome enters the room
<pnkscrooge> ... aren't you going to say something?

Graveyard

* epochsyettocome points

Graveyard

* epochsyettocome points

Graveyard

* epochsyettocome points

Graveyard

* epochsyettocome points

Graveyard

* epochsyettocome points
<pnkscrooge> I can change, and Rust can too!

Footnote

I am not actually worried about Rust "dying."

  • "Work of Fiction" yadda yadda yadda

Our community is super-charged

and we have "Friends in High Places"

The End of It

Acccepting Change

<pnkscrooge> Cratchit, I now see: *life* is change!
<acrichto> ... again, that's not my name.

All recognized that this was a new Scrooge, reformed in his thinking (though not his memory)

Fundamentally different from the man from a year before

One might even call him: a Scrooge for 2018

Epilogue

<aturon> what has pnkscrooge been ranting about?
<aturon> we aren't going to break any code

What's today, my fine fellow?

Already have:

  • nightly/stable split
  • rapid release cycle, and
  • support for deprecation of outdated API's.

Allow Rust to evolve over time, while keeping old code working

However:

  • insufficient for some kinds of changes.

  • allowed changes come at their own pace; Rust evolves gradually and each release is "a somewhat ho hum affair."

Epochery

(RFC 2052)

Rust project will declare an epoch every two or three years

Each epoch provides

  • coherent set of new features and APIs, stabilized since last epoch

  • where tooling, docs and stdlib are updated to mesh with new features

Having compatibility cake and eating it too

Backwards incompatible changes only available if crate opts into epoch in its Cargo.toml, e.g.

epoch = "2019"

Otherwise tools assume 2015 epoch.

Rust compilers must support all extant epochs

Crate graph may involve many epochs at once; must be able to link code and preserve semantics.

Each epoch can introduce hard error only if preceding epoch issued a deprecation warning for same input.

Epochs do not split ecosystem, nor do they break existing code.

Epochs let us consider new changes

  • catch (currently implemented as do catch)

  • deduce module hierarchy from filesystem

  • dyn Trait

  • visibility (crate fn foo instead of pub(crate) fn foo)

Note: epochs will largely focus on syntactic changes

  • syntax change can enable semantic change
  • still need to link old and new code together with coherent result
  • how you read/write code may change, but mental model should not

impl Future for Rust

None of this can happen without our awesome community!

We're encouraging everyone (at every level of knowledge) to get involved during our 2017 impl-period. This is the perfect time to dive in and get some mentorship on a bug.

CHANGE

Conclusion

Don't be like Scrooge { epoch = 2015 }

(yes, we know change is hard)

Be like Scrooge { epoch = 2018 }

change can be hard fun

lets get impl'ing! (but first we fest!)

CHANGE