path: root/why-rust.md

# About me

* Been programming since April, 1984

* BASIC, Pascal, a lot of C, a little C++, various Unix shells, AWK, a
  taste of FORTRAN77, a smidgen of Perl, a lot of Python, a bit of
  Lisp, a little Haskell, a little Go, and now Rust

* I really like Rust

-----------------------------------------------------------------------------

# About Rust

* systems programming

* emphasis on safety, performance

* a bit like C and Haskell had a baby

* Cargo build tool and dependency manager

* long-term stability: editions

* a lively ecosystem of libraries ("crates")



-----------------------------------------------------------------------------

# Why I like Rust: strong, static, versatile typing

* prevents entire classes of bugs: NULL pointer errors, unchecked
  error returns, implicit but wrong value conversions, data races

* "if a program compiles, it usually works" (not really)

-----------------------------------------------------------------------------

# Why I like Rust: type inference

* less typing, more power

* mostly only need to specify function signatures, structs, and
  similar parts and the compiler deduces the rest

* also infers lifetimes when it's unambiguous

-----------------------------------------------------------------------------

# Why I like Rust: memory management

* manual, a la C: malloc, free

  - error prone: easy to leak (no free), easy to break (more than one
    free, or use after free), hard to debug

* automatic, with garbage collection

  - Lisp, Python, Go, Java, ...
  - requires a runtime
  - despite decades of research, inevitably there is overhead and
    short pauses

* Rust: automatic, with borrow checker, lifetimes

  - all heap values heap are tied to values on the stack
  - when on-stack value is freed, the heap value is dropped
  - requires making sure stack values have the right lifetimes
  - compiler can prove lack of data races
  - bonus: mutability must be declared explicitly

-----------------------------------------------------------------------------

# Why I like Rust: random bits 

* not controlled by a mega-corporation
* the `?` operator and the `Result` type
* the `Option` type
* enums are powerful, not just names for integers
* pattern matching is powerful and exhaustive
* no OOP, but traits
* zero cost abstractions actually work
* binaries execute quickly
* excellent concurrency support

-----------------------------------------------------------------------------

# Why I like Rust: tooling, ecosystem, community

* `cargo` works well and avoids most pitfalls other language package
  managers have

* culture of good documentation, with doctests

* things keep getting better, without breaking things

* avoids the 20/80 principle: problems are solved thoroughly
  - culture avoids "pragmatic shortcuts" to allow implementation to be
    simpler, if the shortcut would be likely to bite users

* the community is friendly and constructive and lively

-----------------------------------------------------------------------------

# Not everything is perfect: Rust is not finished

* language and libraries change

  - rustup install/update preferred over distro packages
  - new language release every six weeks

* fairly young

  - Rust: 2010 (1.0 in 2015)
  - Go: 2009
  - C#: 2000
  - PHP, Java, JavaScript: 1995
  - Python: 1991
  - Haskell: 1990
  - Perl: 1987
  - C: 1972
  - Lisp: 1958
  - Fortran: 1957
  - Plankalkül: 1948


-----------------------------------------------------------------------------

# Not everything is perfect: portability, etc

* supports a fraction of the targets of C

  - but all the big mainstream ones are supported

* de facto static linking only
  - dynamic linking works, but Rust ABI is not yet stable, so static
    is the default

* compilation is slow

-----------------------------------------------------------------------------

# Example: hello.rs (self-standing)

```{.rust .numberLines}
fn main() {
    println!("Hello, world!");
}
```

Compiled with the Rust compiler directly:

~~~{.sh .numberLines}
$ rustc hello.rs
$ ./hello
Hello, world!
$
~~~

-----------------------------------------------------------------------------

# Example: hello with Cargo

* `cargo` is the Rust build tool and dependency manager

* `cargo init`

* minimum files

  * `Cargo.toml`
  * `src/main.rs`

-----------------------------------------------------------------------------

# Example: hello with Cargo: `Cargo.toml`

~~~{.toml .numberLines}
[package]
name = "hello"
version = "0.1.0"
authors = ["Lars Wirzenius <lwirzenius@wikimedia.org>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
~~~

-----------------------------------------------------------------------------

# Example: hello with Cargo: `src/main.rs`

~~~{.rust .numberLines}
fn main() {
    println!("Hello, world!");
}
~~~

-----------------------------------------------------------------------------

# Example: hello with Cargo: commands

~~~{.sh .numberLines}
$ cargo init --bin hello
$ cd hello
$ cargo run
   Compiling hello v0.1.0 (/home/liw/wmf/talks/x/hello)
    Finished dev [unoptimized + debuginfo] target(s) in 0.37s
     Running `target/debug/hello`
Hello, world!
$ cargo run -q
Hello, world!
$
~~~

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# Long example: summain

A real program. Outputs a _manifest_ with metadata about files named
on the command line. Testing tool for backup software. Uses
concurrency (threads) for speed.

\ 

Actual source code: [`https://gitlab.com/larswirzenius/summain`](https://gitlab.com/larswirzenius/summain)

-----------------------------------------------------------------------------

# Summain output, sample

~~~{.yaml .numberLines}
---
path: "./COPYING"
mode: "-rw-rw-r--"
mtime: 1613482516
mtime_nsec: 369325267
nlink: 1
size: 35147
sha256: 8ceb4b9ee5adedde47b31e975c1d90c73ad27b6b165a1dcd80c7c545eb65b903
target: ~

---
path: src
mode: drwxrwxr-x
mtime: 1613482516
mtime_nsec: 369325267
nlink: 3
size: ~
sha256: ~
target: ~

~~~

-----------------------------------------------------------------------------

# Example: summain: main program, part 1

~~~{.rust .numberLines}
fn main() -> anyhow::Result<()> {
    let mut opt = Opt::from_args();
    opt.pathnames[..].sort();
    let v: Vec<anyhow::Result<ManifestEntry>> =
        opt.pathnames
		.par_iter().map(|p| manifest(&p))
		.collect();
    for m in v {
        let m = m?;
        println!("{}", serde_yaml::to_string(&m)?);
    }
    Ok(())
}
~~~

-----------------------------------------------------------------------------

# Example: summain: main program, part 2

~~~{.rust .numberLines}
#[derive(StructOpt, Debug)]
struct Opt {
    #[structopt(parse(from_os_str))]
    pathnames: Vec<PathBuf>,
}

fn manifest(
  path: &Path
) -> anyhow::Result<ManifestEntry> {
    ManifestEntry::new(path)
	  .with_context(|| format!("{}", path.display()))
}
~~~

-----------------------------------------------------------------------------

Example: summain: `struct ManifestEntry`

~~~{.rust .numberLines}
#[derive(Serialize, Debug)]
pub struct ManifestEntry {
    path: String,
    #[serde(with = "mode")]
    mode: u32,
    mtime: i64,
    mtime_nsec: i64,
    nlink: u64,
    size: Option<u64>,
    sha256: Option<String>,
    target: Option<PathBuf>,
}
~~~

-----------------------------------------------------------------------------

# Example: summain: `impl ManifestEntry`, part 1

~~~{.rust .numberLines}
impl ManifestEntry {
    pub fn new(path: &Path) -> std::io::Result<Self> {
        let m = symlink_metadata(path)?;
        let hash = if m.is_file() {
            Some(file_checksum(path)?)
        } else {
            None
        };
        let target = if m.file_type().is_symlink() {
            Some(read_link(path)?)
        } else {
            None
        };
~~~

-----------------------------------------------------------------------------

# Example: summain: `impl ManifestEntry`, part 2

~~~{.rust .numberLines}
        Ok(Self {
            path: path.to_string_lossy().into_owned(),
            mode: m.st_mode(),
            mtime: m.st_mtime(),
            mtime_nsec: m.st_mtime_nsec(),
            nlink: m.st_nlink(),
            size: if m.is_dir() {
			  None 
		    } else { 
			  Some(m.st_size()) 
		    },
            sha256: hash,
            target,
        })
    }
}
~~~

-----------------------------------------------------------------------------

# Example: summain: `file_checksum`

~~~{.rust .numberLines}
fn file_checksum(path: &Path) -> std::io::Result<String> {
    let mut hasher = Sha256::new();

    let file = File::open(path)?;
    let mut reader = BufReader::new(file);
    let mut buf = vec![0; BUF_SIZE];
    loop {
        let n = reader.read(&mut buf)?;
        if n == 0 {
            break;
        }
        hasher.update(&buf[..n]);
    }
    let hash = hasher.finalize();
    Ok(format!("{:x}", hash))
}
~~~

-----------------------------------------------------------------------------

# Example: summain: `mod mode`

~~~{.rust .numberLines}
mod mode {
    use serde::{self, Serializer};

    pub fn serialize<S>(
	  mode: &u32, 
	  serializer: S
	) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let s = unix_mode::to_string(*mode);
        serializer.serialize_str(&s)
    }
}
~~~

-----------------------------------------------------------------------------

![](htop-summain.png)

-----------------------------------------------------------------------------

# SEE ALSO

**Rust**  
[`https://www.rust-lang.org/`](https://www.rust-lang.org/)

**crates.io**  
[`https://crates.io/`](https://crates.io/)

**Summain**  
[`https://gitlab.com/larswirzenius/summain`](https://gitlab.com/larswirzenius/summain)

**Subplot**  
[`https://gitlab.com/larswirzenius/subplot/`](https://gitlab.com/larswirzenius/subplot/)

**These slides:**  
[`http://git.liw.fi/wmf-talks`](http://git.liw.fi/wmf-talks)

-----------------------------------------------------------------------------


# Legalese


Copyright 2021 Wikimedia Foundation

This content is licensed under the Creative Commons
Attribution-ShareAlike 4.0 International ([CC BY-SA 4.0][]) licence.

[CC BY-SA 4.0]: https://creativecommons.org/licenses/by-sa/4.0/

---
title: "Why Rust?"
subtitle: "A brief introduction"
author: Lars Wirzenius
date: 2021-02-16
...