WILR2: Rust Beginnings (minigrep)

• 20 June 2022
• rust,
• what-i-learned-recently

I learned some basic Rust by following the Rust Book's Chapter 12, where they show us how to build a minigrep command-line application.

What you see below are very rough notes I took as I went through this for the first time. Hopefully this, along with the video walkthrough, is helpful to you in some way.

Timestamps

• 0:00 Intro
• 0:32 Installation
• 0:45 Discussing the Rust Book
• 2:13 The finished code
• 2:44 What it does
• 3:56 Code walkthrough

Installing Rust

https://www.rust-lang.org/tools/install

• Just use script:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

• If having trouble on proxy, use minimal installation
  • (I was having trouble with rust-docs)

Rust Book Ch. 12

https://doc.rust-lang.org/book/ch12-00-an-io-project.html

• Importing standard libraries: you can import std::env::args if you want, but it's not recommended. Better to import std::env to prevent name conflicts
  • Either way, use seems to take the last thing and make it accessable. use std::env makes env accessible, use std::error::Error makes Error accessible
• env::args() returns an iterator, and collect() turns it into a vector (basically a list) so that we can use it
• expect() fails out and prints a rust backtrace (ugly)
• First: Can simply return a tuple
• Then, abstract the tuple to struct Config - this way, you can name your fields
• Adding impl Config, and new method: Allows you to "instantiate" the Config object using args
• Checking for errors: Can panic!(), which is like expect! in that it prints a backtrace (ugly)
• Alternative: Return a Result and let the caller handle it. Ok() with return value or Err() with message
  • What is &'static ?? something to do with reference/memory ownership I think
  • It says to see Chapter 10 on "Lifetimes": https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html
• unwrap_or_else: Alternative to expect()
  • expect() gives you the return value in Result, or panics
  • unwrap_or_else gives you the return value if ok, otherwise lets you handle it in a block of code
  • "custom, non-panic error handling"
  • Uses a Closure, or anonymous function
• std::process lets you exit with error code, much like python's sys.exit
• Box<dyn Error> is a trait object
  • Basically means what it returns must be a subclass of Error
  • Ending a line with ? instead of expect(): Returns the error automatically instead of panicking
• if let syntax?? Similar to unwrap_or_else?
• We move our code to separate lib.rs file - it calls this a separate crate? This way, it can be tested. Added pub everywhere
• Tutorial uses TDD! My heart!
• Lifetime 'a marks the argument with matching lifetime of return value. So return value will live as long as the contents variable
  • Again, see Chapter 10 on "Lifetimes": https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html
• Topics covered: file input and output, lifetimes, testing, and command line parsing.
• Env to add case sensitivity
• Print to stderr with eprintln!

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