Preston Maness ☭

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  • 2 Posts
  • 94 Comments
Joined 3 years ago
Cake day: March 2nd, 2022
  • Preston Maness ☭@lemmygrad.mltoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"English
    1·
    2 months ago

    I’ll try :) Looks like I still have my code from when I was grinding through The Book, and there’s a couple spots that might be illuminating from a pedagogical standpoint. That being said, I’m sure my thought process, and “what was active code and what was commented out and when,” will probably be hard to follow.

    My first confusion was in deref coercion auto dereferencing (edit: see? it’s still probably not 100% in my head :P), and my confusion pretty much matched this StackOverflow entry:

    https://stackoverflow.com/questions/28519997/what-are-rusts-exact-auto-dereferencing-rules

    It took me until Chapter 15 of The Book (on Boxes) to really get a feel for what was happening. My work and comments for Chapter 15:

    use crate::List::{Cons, Nil};
use std::ops::Deref;

enum List {
    Cons(i32, Box<List>),
    Nil,
}

struct MyBox<T>(T);

impl<T> Deref for MyBox<T> {
    type Target = T;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<T> MyBox<T> {
    fn new(x: T) -> MyBox<T> {
        MyBox(x)
    }
}

#[derive(Debug)]
struct CustomSmartPointer {
    data: String,
}

impl Drop for CustomSmartPointer {
    fn drop(&mut self) {
        println!("Dropping CustomSmartPointer with data `{}`!", self.data);
    }
}

fn main() {
    let b = Box::new(5);
    println!("b = {}", b);

    let _list = Cons(1, Box::new(Cons(2, Box::new(Cons(3,Box::new(Nil))))));

    let x = 5;
    let y = MyBox::new(x);

    assert_eq!(5,x);
    assert_eq!(5, *y);

    let m = MyBox::new(String::from("Rust"));
    hello(&m);
    hello(m.deref());
    hello(m.deref().deref());
    hello(&(*m)[..]);
    hello(&(m.deref())[..]);
    hello(&(*(m.deref()))[..]);
    hello(&(*(m.deref())));
    hello((*(m.deref())).deref());

    // so many equivalent ways. I think I'm understanding what happens
    // at various stages though, and why deref coercion was added to
    // the language. Would cut down on arguing over which of these myriad
    // cases is "idomatic." Instead, let the compiler figure out if there's
    // a path to the desired end state (&str).

    // drop stuff below ...
    let _c = CustomSmartPointer {
        data: String::from("my stuff"),
    };
    let _d = CustomSmartPointer {
        data: String::from("other stuff"),
    };

    println!("CustomSmartPointers created.");
    drop(_c);
    println!("CustomSmartPointer dropped before the end of main.");

    // this should fail.
    //println!("{:?}", _c);
    // yep, it does.

}

fn hello(name: &str) {
    println!("Hello, {name}!");
}

    Another thing that ended up biting me in the ass was Non-Lexical Lifetimes (NLLs). My code from Chapter 8 (on HashMaps):

    use std::collections::HashMap;

fn print_type_of<T>(_: &T) {
    println!("{}", std::any::type_name::<T>())
}

fn main() {
    let mut scores = HashMap::new();
    scores.insert(String::from("Red"), 10);
    scores.insert(String::from("Blue"), 20);

    let score1 = scores.get(&String::from("Blue")).unwrap_or(&0);
    println!("score for blue is {score1}");
    print_type_of(&score1); //&i32
    let score2 = scores.get(&String::from("Blue")).copied().unwrap_or(0);
    println!("score for blue is {score2}");
    print_type_of(&score2); //i32

    // hmmm... I'm thinking score1 is a "borrow" of memory "owned" by the
    // hashmap. What if we modify the blue teams score now? My gut tells
    // me the compiler would complain, since `score1` is no longer what
    // we thought it was. But would touching the score of Red in the hash
    // map still be valid? Let's find out.

    // Yep! The below two lines barf!
    //scores.insert(String::from("Blue"),15);
    //println!("score for blue is {score1}");

    // But can we fiddle with red independently?
    // Nope. Not valid. So... the ownership must be on the HashMap as a whole,
    // not pieces of its memory. I wonder if there's a way to make ownership
    // more piecemeal than that.
    //scores.insert(String::from("Red"),25);
    //println!("score for blue is {score1}");

    // And what if we pass in references/borrows for the value?
    let mut refscores = HashMap::new();
    let mut red_score:u32 = 11;
    let mut blue_score:u32 = 21;
    let default:u32 = 0;
    refscores.insert(String::from("red"),&red_score);
    refscores.insert(String::from("blue"),&blue_score);

    let refscore1 = refscores.get(&String::from("red")).copied().unwrap_or(&default);
    println!("refscore1 is {refscore1}");

    // and then update the underlying value?
    // Yep. This barfs, as expected. Can't mutate red_score because it's
    // borrowed inside the HashMap.
    //red_score = 12;
    //println!("refscore1 is {refscore1}");

    // what if we have mutable refs/borrows though? is that allowed?
    let mut mutrefscores = HashMap::new();
    let mut yellow_score:u32 = 12;
    let mut green_score:u32 = 22;
    let mut default2:u32 = 0;
    mutrefscores.insert(String::from("yellow"),&mut yellow_score);
    mutrefscores.insert(String::from("green"),&mut green_score);
    //println!("{:?}", mutrefscores);

    let mutrefscore1 = mutrefscores.get(&String::from("yellow")).unwrap();//.unwrap_or(&&default2);
    //println!("{:?}",mutrefscore1);
    
    println!("mutrefscore1 is {mutrefscore1}");

    // so it's allowed. But do we have the same "can't mutate in two places"
    // rule? I think so. Let's find out.

    // yep. same failure as before. makes sense.
    //yellow_score = 13;
    //println!("mutrefscore1 is {mutrefscore1}");

    // updating entries...
    let mut update = HashMap::new();
    update.insert(String::from("blue"),10);
    //let redscore = update.entry(String::from("red")).or_insert(50);
    update.entry(String::from("red")).or_insert(50);
    //let bluescore = update.entry(String::from("blue")).or_insert(12);
    update.entry(String::from("blue")).or_insert(12);


    //println!("redscore is {redscore}");
    //println!("bluescore is {bluescore}");
    println!("{:?}",update);

    // hmmm.... so we can iterate one by one and do the redscore/bluescore
    // dance, but not in the same scope I guess.
    let mut updatesingle = HashMap::new();
    updatesingle.insert(String::from("blue"),10);
    for i in "blue red".split_whitespace() {
        let score = updatesingle.entry(String::from(i)).or_insert(99);
        println!("score is {score}");
    }

    // update based on contents
    let lolwut = "hello world wonderful world";
    let mut lolmap = HashMap::new();
    for word in lolwut.split_whitespace() {
        let entry = lolmap.entry(word).or_insert(0);
        *entry += 1;
    }

    println!("{:?}",lolmap);

    // it seems like you can only borrow the HashMap as a whole.
    // let's try updating entries outside the context of a forloop.

    let mut test = HashMap::new();
    test.insert(String::from("hello"),0);
    test.insert(String::from("world"),0);
    let hello = test.entry(String::from("hello")).or_insert(0);
    *hello += 1;
    let world = test.entry(String::from("world")).or_insert(0);
    *world += 1;

    println!("{:?}",test);

    // huh? Why does this work? I'm borrowing two sections of the hashmap like before in the update
    // section.
    
    // what if i print the actual hello or world...
    // nope. barfs still.
    //println!("hello is {hello}");

    // I *think* what is happening here has to do with lifetimes. E.g.,
    // when I introduce the println macro for hello variable, the lifetime
    // gets extended and "crosses over" the second borrow, violating the
    // borrow checker rules. But, if there is no println macro for the hello
    // variable, then the lifetime for each test.entry is just the line it
    // happens on.
    //
    // Yeah. Looks like it has to do with Non-Lexical Lifetimes (NLLs), a
    // feature since 2018. I've been thinking of lifetimes as lexical this
    // whole time. And before 2018, that was correct. Now though, the compiler
    // is "smarter."
    //
    // https://stackoverflow.com/questions/52909623/rust-multiple-mutable-borrowing
    //
    //   https://stackoverflow.com/questions/50251487/what-are-non-lexical-lifetimes
    //let 
}
  • Preston Maness ☭@lemmygrad.mltoPrivacy@lemmy.ml•Signal Is More Than Encrypted Messaging. Under Meredith Whittaker, It’s Out to Prove Surveillance Capitalism WrongEnglish
    3·
    2 months ago

    If that were the case Molly FOSS wouldn’t exist

    I’m not speaking of hard dependence as in “the app can’t work without it.” I’m speaking to the default behavior of the Signal application:

    1. It connects to Google
    2. It does not make efforts to anonymize traffic
    3. It does makes efforts to prevent anonymous sign-ups

    Molly FOSS choosing different defaults doesn’t change the fact that the “Signal” client app, which accounts for the vast majority of clients within the network, is dependent on Google.

    And in either case – using Google’s Firebase system, or using Signal’s websocket system – the metadata under discussion is still not protected; the NSA doesn’t care if they’re wired into Google’s data centers or Signal’s. They’ll be snooping the connections either way. And in either case, the requirement of a phone number is still present.

    Perhaps I should restate my claim:

    Signal per se is not the mass surveillance tool. Its dependence on Google design choices of (1) not forcing an anonymization overlay, and (2) forcing the use of a phone number, is the mass surveillance tool.

  • Preston Maness ☭@lemmygrad.mltothe_dunk_tank@hexbear.net•Lemmy.world offically enshrines the siteadmins' right to futher remove "misinformation" at will after an admin overthrew its vegan comm.English
    4·
    2 months ago

    READ THE STUDY!

    No need to shout. I did.

    So you’re saying that vegan cats had roughly the same health as non vegan cats

    No. That is not what the study is saying. The study is saying that “we took a look, and couldn’t tell if there was a difference or not.” Which is understandable, given the methodology. Internet-based questionnaires/surveys are easy to conduct, but tend to have big error bars. It’s a common trade-off made when first beginning to investigate a hypothesis.

    It’s your typical “absence of evidence” versus “evidence of absence” conundrum. The authors note this in their comments on the limitations of their study and on avenues for further research:

    As we’ve noted previously [30], large-scale cross-sectional or ideally, longitudinal studies of cats maintained on different diets, utilising objective data, such as results of veterinary clinical examinations and laboratory data, as well as veterinary medical histories, should yield results of greater reliability, if sufficient funding could be sourced.

    and we’re not destroying our planet in industrial livestock murder. Sounds great!

    Comrade, I’m not trying to argue that cats are “obligate carnivores,” or that cats should or should not have vegan diets. I’m not arguing about whether or not cats can meet their nutritional needs from vegan diets. I am only stating that the particular study linked does not provide any usable evidence in support of a conclusion. That’s literally what “no reductions were statistically significant” means: that the collected data is not sufficient to draw reliable conclusions.

    Other studies may very well have more rigorous methodologies that convincingly demonstrate the nutritional completeness of vegan diets for cats. But not this study.