What is Rust doing behind the curtains?

This is an hands-on talk, showing a journey from code with a lot of syntactic sugar to plain, veeery explicit Rust code.

Rust allows for a lot of syntactic sugar, that makes it a pleasure to write. It is sometimes hard, however, to look behind the curtain and see what the compiler is really doing with our code. "It is good to know what these conveniences are, to avoid being mystified by what's going on under the hood... the less magical thinking we have of the world, the better." (Tshepang Lekhonkhobe). In this hands-on talk, we will go from code with a lot of syntactic sugar to extremely verbose Rust code.

We will use a little tool called `cargo-inspect`, which was built for teaching Rust internals. The goal is to make the compiler more approachable to mere mortals.

Transcript

1. What Is Rust Doing
   Behind the Curtains?
   

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2. Matthias Endler
   !2
   Hi! I am
   You might know me from...
   My YouTube channel! My Blog! Not at all!
   

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3. • Hotel Search Platform
   • 2.5m+ Hotels/Accommodations
   • IT departments in Düsseldorf, Leipzig, Palma, Amsterdam
   • Java, Kotlin, Go, PHP, Python (, Rust?)
   • tech.trivago.com
   

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4. Why should I care?
   !4
   

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5. Rust is a systems programming language that runs
   blazingly fast, prevents segfaults, and guarantees thread
   safety. It aims to bring modern language design and an
   advanced type system to systems programming. Rust
   does not use a garbage collector, using advanced static
   analysis to provide deterministic drops instead.
   

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6. Rust is a systems programming language that runs
   blazingly fast, prevents segfaults, and guarantees thread
   safety. It aims to bring modern language design and an
   advanced type system to systems programming. Rust
   does not use a garbage collector, using advanced static
   analysis to provide deterministic drops instead.
   

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7. Empowering everyone
   to build reliable and
   efficient software.
   

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8. Be curious.
   Try crazy things.
   Don't be afraid.
   

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9. !9
   

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10. Being curious is an amazing trait!
    We should embrace it,
    and help people be curious.
    Pascal Hertleif –

    Rust’s approach of getting things right
    

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11. Julia Evans
    

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12. Why's Poignant Guide to Ruby
    

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14. The Rust Compiler
    !14
    

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15. !15
    RUST SOURCE
    HIR
    Parsing

    Desugaring
    MIR
    Borrow-checking

    Optimization
    LLVM IR
    Optimization
    MACHINE CODE
    Optimization
    

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16. !16
    RUST SOURCE
    HIR
    Parsing

    Desugaring
    MIR
    Optimization
    LLVM IR
    MACHINE CODE
    Optimization
    Borrow-checking

    Optimization
    HAIR
    Optimization
    

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17. Desugaring...
    Candy designed by Freepik, Vegetables by Macrovector
    

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18. Code examples!
    At last...
    !18
    

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19. Example1
    

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20. fn main() {}
    

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21. #[macro_use]
    extern crate std;
    #[prelude_import]
    use std::prelude::v1::*;
    fn main() {}
    

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22. std::boxed::Box
    std::option::Option::{self, Some, None}
    std::result::Result::{self, Ok, Err}
    std::string::String;
    std::vec::Vec
    std::borrow::ToOwned
    std::clone::Clone
    std::cmp::{PartialEq, PartialOrd, Eq, Ord }
    std::convert::{AsRef, AsMut, Into, From}
    std::default::Default
    std::iter::{DoubleEndedIterator, ExactSizeIterator}
    std::iter::{Iterator, Extend, IntoIterator}
    std::marker::{Copy, Send, Sized, Sync}
    std::ops::{Drop, Fn, FnMut, FnOnce}
    std::slice::SliceConcatExt
    std::string::ToString
    std::mem::drop
    Types:
    Traits:
    Functions:
    

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23. Box, Option, Result, String, Vec
    PartialEq, PartialOrd, Eq, Ord

    AsRef, AsMut, Into, From, ToOwned, Clone, ToString

    Default

    DoubleEndedIterator, ExactSizeIterator
    Iterator, Extend, IntoIterator

    Copy, Send, Sized, Sync

    Drop, Fn, FnMut, FnOnce

    SliceConcatExt
    Types:
    Traits: Ordering things
    Converting things
    Default values
    Marker traits
    Calling/Dropping objects
    Concatenate objects

    (like strings or vectors)
    Iteration
    

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24. Example2
    Ranges
    

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25. for i in 0..3 {
    // do something with i
    }
    

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26. let range = 0..3;
    for i in range {
    // do something with i
    }
    

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27. let range = Range {0, 3};
    for i in range {
    // do something with i
    }
    

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28. let range = Range {0, 3};
    for i in range {
    // do something with i
    }
    

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29. use std::ops::Range;
    let range = Range { start: 0, end: 3 };
    for i in range {
    // do something with i
    }
    

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30. use std::iter::IntoIterator;

    use std::ops::Range;
    let range = Range { start: 0, end: 3 };
    let mut iter =
    IntoIterator::into_iter(range);
    while let Some(i) = iter.next() {
    // do something with i
    }
    

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31. use std::iter::IntoIterator;
    use std::ops::Range;
    let range = Range { start: 0, end: 3 };
    let mut iter =
    IntoIterator::into_iter(range);
    loop {
    match iter.next() {
    Some(i) => { /* use i */ },
    None => break,
    }
    }
    

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32. cargo inspect
    

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33. !33
    cargo-install cargo-inspect

    cargo inspect foo.rs
    

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34. Example3
    Ranges - Part II
    

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35. for i in 0..=3 {
    // do something with i
    }
    

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36. use std::iter::IntoIterator;
    use std::ops::RangeInclusive;
    let range = RangeInclusive::new(0, 3);
    let mut iter =
    IntoIterator::into_iter(range);
    loop {
    match iter.next() {
    Some(i) => { /* use i */ },
    None => break,
    }
    }
    

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37. cargo inspect --diff foo.rs,bar.rs
    !37
    

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38. Example4
    Opening Files
    

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39. use std::fs::File;
    use std::io::Error;
    fn main() -> Result<(), Error> {
    let f = File::open("file.txt")?;
    Ok(())
    }
    

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40. use std::fs::File;
    use std::io::Error;
    fn main() -> Result<(), Error> {
    let f = match File::open("file.txt") {
    Ok(file) => file,
    Err(err) => return Err(err),
    };
    Ok(())
    }
    

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41. use std::fs::File;
    use std::io::Error;
    use std::convert::From;
    fn main() -> Result<(), Error> {
    let f = match File::open("file.txt") {
    Ok(file) => file,
    Err(err) => return Err(From::from(err)),
    };
    Ok(())
    }
    

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42. cargo-inspect-vscode
    

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43. More cargo tools!
    !43
    • cargo-expand
    • cargo-asm
    • cargo-bloat
    

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44. Rust Playground
    !44
    

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45. !45
    play.rust-lang.org
    

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46. Compiler Explorer
    !46
    

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47. !47
    godbolt.org
    

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48. Lessons Learned
    • Rust allows for lots of syntactic sugar
    • It's good to be reminded about that sometimes
    • Tools help us understand what's going on
    behind the curtains.
    !48
    

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49. !49
    Now go and build cool things!
    

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51. Credits
    •Stage background from freepik.com designed by
    starline
    •Lucy with a Rocket engine
    •Rustlang MIR documentation
    •Rust compiler guide
    !51
    

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