social.noyu.me

exciting programming problem in touchHLE: supporting inheritance for instance variables. look at how gnarly this is:

https://github.com/hikari-no-yume/touchHLE/commit/ae5b7a8d6513e3204d3c2eab1f250cdcf8930ee5

i have an idea for a neater solution, but it will involve descending further into the land of Anys and 'statics and 'as and dyns :3

THE BAD NEWS: i have ran head-first into the borrow checker struggling with mutable borrows in loops again ;_;
THE GOOD NEWS: unsafe { &mut *(a as *mut _) } is my friend and would never hurt me :3

@hikari are you running Miri on this to find out if it would hurt you

@porglezomp but it's simple enough that i know it must be safe. there is never an actually overlapping mutable borrow, and the lifetimes are all identical

@hikari
• use miri it’s also your friend
• if it’s so obvious surely you can make it obvious to the compiler also

@porglezomp AIUI it's a known limitation of the borrow checker, it simply cannot handle a loop that updates mutable borrows with early returns, or something like that :(

@porglezomp I've run into it multiple times before and this time I just don't have any patience for it. I do not want to play the game of making my code comically inefficient just to work around this limitation of rustc.

@hikari @porglezomp for some reason I'm suspicious this is related to split borrows or something. and might work with deleting the wrapper functions. don't know it for certain though.

@hikari @porglezomp a little rustc fairy suggests the original code will probably compile with -Z polonius, and it is indeed a current-rustc limitation. but it won't be a future one, at some point! https://crates.io/crates/polonius-the-crab/0.3.1