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Chapter 1

(omitted for brevity)

Chapter 2: Tour of Rust

  • Typical for function's return value to "fall off the end of the function"

  • Tests marked with #[test] attribute

  • Trait is a collection of methods that types can implement

  • Iterators common in rust

  • Rust doesn't have exceptions; handle using Result or panic.

  • By conventions modules named prelude mean its exports are intended to be used together, provide what you need.

  • _ tells rust that a variable will be unused, so it doesn't complain.

  • r#"..." is rusts "raw string" syntax. can use matching numbers of hash marks.

  • cargo run does everything: fetches crates, compiles, builds, links, and starts

  • if your program compiles, it's free of data races

  • Result and Option are the two maybe-ish data types that rust mostly uses

  • /// to start a documentation comment

  • common to init a structs fields with variables of same name. similar to typescript.

  • "[fallible functions in Rust should return a Result, which is Ok(x) on success, or Err(e) on failure]"

  • ? operator checks and panics. don't use in main function

  • |thing| { ... } is a Rust closure expression - value that can be called as if it were a function

  • use move keyword in front of closures to let closure take ownership of variables it uses

Chapter 3: Basic Types

  • Rust pushes everything it can to ahead-of-time compilation for safety

  • Can use generics, and can infer a lot of things for you so you don't have to spell everything out

  • can use underscores in long digits for legibility: 1_000_000

  • can convert integer types between each other using the as operator

  • method calls have higher precedence that unary prefix operators

  • "rust performs no numeric conversions explicitly"

  • tuple is number of values of assorted types - like python

  • tuples accessed via index: t.0 or t.8 etc

  • rust often uses tuples when returning multiple types from a function

  • zero tuple is () and called a "unit type"

  • three pointer types: reference, boxes, and unsafe pointers

  • "reference is a pointer to any value anywhere"

  • references are never null

  • &T is an immutable reference

  • &mut T is a mutable reference

  • boxes allocate a new value to the heap

  • when boxes go out of scope the memory is freed immediately, unless they get moved

  • raw pointers are unsafe, and they might be null so be careful

  • use raw pointers only in unsafe block where safety is up to you

  • rust has three types for representing sequences of values in memory: arrays, vectors, and slices

  • array: constant size determined at compile time; can't append or shrink

  • vector: dynamically allocated, growable

  • slice: series of elements apart of some other value, like array of vector

  • slices are considered shared or mutable: not both.

  • rust has no notation for an uninitialized array.

  • create vectors with the vec! macro

  • vectors are made of: pointer to heap allocated buffer, capacity, and length

  • slices are a region of array or vector, made of a fat-pointer (two word value: pointer to first element, number of elements)

  • strings are stored as UTF-8: Vec

  • &str is really just a ref of some utf-8 text owned by another thing

  • String is different from &str. String is basically Vec

  • when String goes out of scope buffer is freed, unless it was moved and is still owned, which brings us to....

Chapter 4: Ownership

  • every single value has an owner that determines lifetime

  • no garbage collection, or just throwing values around

  • when value is freed it is "dropped" -> allows us to look at code to see lifetime instead of guessing or inspecting comments, etc.

  • "[variables own their values, structs own their fields, tuples, arrays and vectors own their elements]"

  • basically trees: value's owner is parent, values owned are children

  • so when dropping values, Rust is removing it from tree to free it

  • you can "move" values from one owner to another

  • no multiple owners, which Rc and Arc being exceptions

  • you can "borrow" references though; references are non-owning pointers with limited lifetimes

  • in Rust; most of the time assigning, passing, and returning don't copy the value, they move it

  • compiler will complain about moving it more than once unless you returned it

  • "[price you pay is that you have to explicitly as for copies if you need/want them]"

  • if you have a mutable variable however, rust drops prior value on reassignment

  • in general: "[passing arguments to functions moves ownership to the functions parameters; returning a value from a function moves ownership to the caller]"

  • same for building tuples, etc.

  • things to remember about moves: 1) moves apply to value proper, NOT heap storage, 2) Rust's compile sees through moves, so they're pretty efficient

  • in general: if you move something into a function, move it back if you want it back

  • moving index content gets rejected: vectors and arrays for example. what you usually want is a reference

  • ownership applies to scope too; for loops for example take ownership

  • "[if you need to move value out of owners that compilers can't track, you should probably change the owners type to something that can dynamically track whether it has a value or not]"

  • while most types are moved, some values are Copy types; source of assignment stays the same,

  • passing Copy types to constructors behaves similarly: source stays the same

  • "Only types for which a simple bit-for-bit copy can be Copy"

  • in general: any any type that needs something special to be done when the value is dropped, can't be Copy.

  • you can derive from Copy if all the fields of a struct are Copy

  • Copy types are more flexible, but they're also strict about which types they can contain: only Copy-able

  • important! -> if you use Copy, but need to change it later, it'll be difficult to re-write the code to do non-copy stuff.

  • for shared ownership there is: Rc: reference counted, and Arc for atomic reference counted. let you do thread-safe ownership sharing.

  • cloning Rc doesn't create a new one, just a new pointer

Chapter 5: References

  • references are non-owning pointers that have no effect on their referents lifetimes

  • a reference to a value is borrowing the value, and you must eventually return it to its owner

  • shared reference: read but not modify. eg: &T, think: multiple readers at compile time

  • mutable reference: both read and modify: eg: &mut T, think: single writer at compile time

  • mutable borrow = pass by value

  • reference = pass by reference

  • assigning to a reference makes it point at a new value

  • "[the . follows as many references as it takes to find its target]"

  • references are never null (no NPE!)

  • another kind of fat pointer is a trait object: a reference to a value that implements a certain trait

  • "[Rust tries to assign each reference type in your program a lifetime that meets the constraints imposed by how it is used]"

  • basically; a variable's lifetime must contain that of the reference borrowed from it. so start by understanding the constraints from references, then find lifetimes that satisfy those constraints

  • static = rust's global variable, created when the program starts, lasts until termination

  • lifetime parameters = specify lifetimes in generics and traits using f<'a>(p: &a' i32){...} which lets Rust track lifetimes explicitly. only need to do in definitions, not in usage.

  • A function's signature always exposes the body's behavior

  • Lifetimes in functions signatures are so Rust's compiler can ensure safety

  • when a reference type appears inside another type's definition, you need to write out the lifetime

  • "[for a lifetime, a shared reference makes its referent read-only; you can't assign the referent or move its value]"

  • a mutable reference borrow, and a shared reference borrow cannot have overlapping lifetimes (can't borrow a mutable reference to a read-only value)

  • shared access is read-only access, mutable access is exclusive access

  • all of this ensures that a concurrent Rust program is free of data races by construction (at compile time)

  • rust is an expression language: for example, if and match can produce values

  • blocks can also produce values, and can be an explicit way to marking lifetimes inside another function or block

  • variables can be redeclared, but probably don't do it.

  • item declarations: any declaration that could appear globally, like fn

  • match expressions are like switches but better because you can do patterns, they return things

  • in match a value is checked against each pattern in order; must match one pattern

  • four types of loops: while, while let, loop, for

  • for loops use iterable Range: eg: 0..9

  • can use break but it only works in loops

  • can use continue to advance to the next iteration of loop

  • can label loops with lifetimes

  • expressions that don't finish have special return type ! but it's rarely used - divergent functions

  • "[ the . operator automatically dereferences or borrows as many references as needed ]"

  • static methods: Vector::new or if it's typed, use "turbo fish" : Vector::<Thing>new

  • fields accessed via dot name, elements in tuples accessed via index

  • lvalues = access array or slice by index like thing[i]

  • using range .. operator allows open on either end: 0..4 or ..4 or 0.. or ..

  • * operator is used to access value pointed to by a reference

  • dividing by zero triggers a panic. you can do it safely by other means

  • assignment not as common in rust since stuff is immutable

  • if a value has a non-Copy type, then assignment moves it to the destination.

  • Rust doesn't have increment and decrement operators. Good.

  • numbers may be cast to/from any of the built-in numeric types for the most part

  • closures are lightweight function like values, sort of like anonymous functions

Chapter 7: Error Handling

  • most ordinary errors are handled by Result which is either Ok<T> or Err<E>

  • panics are another type of error that should never happen or at least represent something so bad that your program should just be done

  • panics can be handled though. by unwinding: dropping values in the reverse order of creation, all the way up the stack, finally exiting the thread

  • it's not like panics are undefined. panics are defined behavior, they just straight up shouldn't happen. but they are safe.

  • panics happen per thread

  • if, in the process of an unwind, rust panics on a drop, the whole unwinding process is aborted; you messed up while trying to clean up your mess, and you're done, go home.

  • Result<T, E> is best understood with matches, but has easier ways of defaulting, getting values and references, panicking, and so on

  • errors are printable: they have a description and cause (if cause is provided)

  • Rust has ? operator to get a value from a Result, and propagate the error up the stack if any occurs

  • can't use ? in main

  • can use .unwrap() to deal with errors that "can't happen" :)

  • "[.unwrap() is for a condition so severe or bizarre that you don't know what do to.]"

  • use let _ = ... to silence unused var warnings from compiler

  • on the whole; Rust forces you to make decisions about what to do with errors, rather than just throwing them. since they're a part of the return type with Result you have to do something with them

Chapter 8: Crates and Modules

  • "[A crate is a Rust project: all source code for a single library or executable, plus any associated tests, examples, tools, configs]"

  • extern create xyz is like an import statement, but for crates that aren't a part of this project

  • Cargo.toml is the project file: cargo command runs on this, basically doing anything you need to do with a crate

  • crates are bin or lib

  • cargo build builds, cargo build --release builds for release, cargo test tests. those are probably the only ones you need

  • modules are namespaces; containers for functions, constants, and so on. used for organization within a project. can nest them

  • mark things as pub or not. anything not marked pub is private

  • files are modules with their file name. sub-directories are modules of their dir name

  • use to control sub-directory module

  • when you build a rust crate you are compiling all its modules

  • :: operator accesses items inside a module

  • use thing::whatever to use a module

  • each module starts blank, need to import everything it uses

  • super is alias to parent module, self is for this module

  • items: building blocks of rust. are 1) functions, 2) types, 3) type aliases, 4) impl blocks, 5) constants, 6) modules, 7) imports

  • attributes: Rust's catch-all syntax for writing miscellaneous instructions for the compiler. sort of like decorators or annotations in other languages.

  • eg: conditional compilation with #[cfg]

  • can use #! to start attribute to tell Rust to attach it to enclosing item, like module. usually used at the beginning of a file

  • tests use attributes like #[test] to tell cargo which functions are tests so they're conditionally compiled

  • tests usually use macros like assert_eq!(expected, actual)

  • "[by convention keep tests inside same file they're testing, until they get big, then split them into and mark the whole file with #[cfg(test)] so they don't get compiled]"

  • integration tests usually live alongside your /src directory of your project: for testing surface area of your code, as a user would

  • cargo doc creates html documentation from your code from the pub features of your code with any doc comments

  • can use doc comments like /// or you can put them as annotations with #[doc = "comment here"]

  • can use markdown for comments, and they'll get translated to html

  • can also put in fenced code blocks

  • "doc-tests" are checked by rust when generating docs, to ensure that they compile, and run

  • goal is to get you to write the best possible documentation

  • can mark code snippets as no-run to if they're not complete

  • dependencies in Cargo.toml can use the name, a path to a local crate, or a git link to something like GitHub

  • uses semantic versioning

  • Cargo.lock keeps versions the same across installation so deps change only when you want them do

  • cargo update updates versions for crates

  • can also do workspaces, which is just a collection of crates, each with their own .toml

Chapter 9: Structs

  • three: named-field, tuple-like, unit like

  • named-field structs: camel case names, snake case fields. can do shorthand {x, y} to populate fields on construction

  • fields on structs are private by default

  • creating a struct value requires all fields to be initialized

  • can use something like a "spread" syntax, {x=0, ..other}

  • tuple-like structs: camel case name, fields are accessed by index

  • tuple elements private by default, but can be marked public

  • "[good for new-types; structs with a single thing that you use to get stricter type checking]"

  • eg: struct Ascii(Vec<u8>)

  • unit-like structs: struct type with no elements. basically just type MyThing

  • methods on a struct appear in a different block: impl

  • impl block just a collections of fn definitions that become methods on the struct type

  • if they need it, methods are passed self as the first argument, or &self, or &mut self if needed. use only what you need.

  • calling a method on a struct is implicit mutable ref in many cases

  • conventional to have a constructor called new

  • if you want you can attach your own methods to other types

  • methods are separated to: 1) make it easy to find data members, 2) allow single syntax for all struct types, 3) allow implementation of traits

  • rust has generics :)

  • similar to other generic languages: use <T> for type parameters

  • can use Self instead of always spelling out the type

  • for static method calls, used turbo-fish using ::<>

  • if a struct type contains references you must name the references' lifetimes


struct Position<'p> {
 x: & 'p i32,
 x: & 'p i32,
  • which means "for lifetime 'p, you can have a Position that holds references to that lifetime"

  • this lets rust do lifetime constrain checking

  • traits are implemented on an impl block, or defined by themselves

  • think of it as an easier way to do Java abstract classes

  • use #derive[Clone] to derive traits without having to write them

  • for most traits, you can depend on trait inheritance -> as long as all members of a struct impl trait X, you can derive trait X

  • interior mutability is when a struct is immutable, but it has fields that need to be mutable

  • interior mutability is usually done with Cell<T> and RefCell<T> but you can do it with Box<T> too

  • Cell<T> struct that contains a single value of T. can set and get T even if you don't have access to Cell itself

  • Cell<T> doesn't left you call mut methods on the shared value

  • RefCell<T> is like Cell but you can borrow T

  • RefCell does runtime checks, but not compile time checks, so if you break rules it panics

  • neither is thread safe

Chapter 10: Enums and Patterns

  • rust enums can contain data, and data of varying types

  • rust enums offer type safety (something that is really hard if you're doing some types of polymorphic stuff in java, for example)

  • drawback is that you only access them using pattern matching

  • can do numbered enums, or enums that contain fields like structs

  • enums can have methods like structs, just use impl

  • enums can also have struct variants, which have named fields

  • enums can be primitive, tuple-like, or struct-like, or all three

  • classic case for enums is doing polymorphism, or tree-like structures

  • enums can also be generic, type params used on enum cases, etc

  • Rust won't let you access data stored in enums unless you check with match

something like

match x {
 Ok(v) => println!("{}", v)
 Unknown(err) => println!("{}", err),
 _ => panic!("uh oh")
  • patterns consume values, expressions produce values

  • patterns are to the left of =>, expressions are on the right of =>

  • match must be exhaustive. you need to do something for any given match

  • _ is a wildcard pattern and matches everythig

  • you can create variables in patterns, or use literals, but you can use existing variables

  • you can use tuples in patterns, you can use structs in patterns

  • ref patterns borrow parts of a matched value

  • & patterns match references

  • "[patterns and expressions are opposites. eg: (x, y) as a pattern consumes tuple - pulling values, (x, y) as expression creates a tuple]"

  • pattern guards are boolean evaluations added to patterns. but only when you're not moving values

@ pattern matches the pattern, but it moves or copies the entire value into the produced variable

  • irrefutable patterns are patterns that always match

  • "[patterns are a tool designed to get data into the right shape]"

Chapter 11: Traits and Generics

  • traits are Rust's way of doing interfaces or abstract base classes

  • declare traits like an interface:

trait Write {
 fn write() -> Result<usize>;
  • trait generics are related

  • bound is a way of declaring the trait requirements of type params in generics

  • "[trait represents a capability: something a type can do]"

  • (similar to Go's "if it can do that, you can use it here"?)

  • in order for trait to be used, the trait itself must be in scope

  • "[two ways to do polymorphic code: traits and generics]"

  • trait object: reference to a trait type

  • combine trait types using + sign like fn thing<T: Debug + Hash + Eq>() {...}

  • can also use where clause so the type param doesn't get too unreadable

  • also define lifetimes in generic type defs using 'a

  • (side note that lifetimes have no impact on machine code - just tell rust how to check when compiling)

  • individual functions can be generic, even when the type they're defined on is not

  • "[use trait objects when you need a collection of values of mixed types all together]"

  • generics have the advantage of speed: don't need dynamic dispatch

  • another advantage of generics is not every trait can work on trait objects

  • defining traits is basically defining an interface: just types

  • extension traits: adding methods to existing types, similar to java's extending other classes, but without rename

  • can use Self in types as shorthand

  • can define traits that extend other traits, like this:

trait Thing: Other {
  • traits can have static methods and constructors

  • fully qualified method calls can be called right off of the type: str::to_string("Hello")

  • use these when: 1) two methods have the same name, 2) when the type of the self-arg can't be inferred, 3) calling traits in macros

  • associated types: sort of like scoped types, or related types. used iterables. similar to java's "T extends E" in an abstract class

  • useful when placing bounds in a where clause

  • "[associated types perfect for cases where implementation has one specific related type]"

  • buddy traits: traits designed to work together

  • overall: generics and traits stop you from braking other code. as long as types are the same, implementation can change

Chapter 12: Operator Overloading

  • (side note: this isn't in the book, but operator overloading is hard, a little confusing, and probably something you should read a whole book about before you ever consider doing it. get some domain specific knowledge, and a solid use case, and maybe then you should do it.)

  • useful for comparing complex structs using ordered comparisons

  • PartialEq or Eq or Ordering

  • can specify how index operations like a[i] work using Index and IndexMut

  • be careful: overloading can be difficult to debug

Chapter 13: Utility Traits

  • big ones are Drop, Sized, Clone, Copy, Deref, DerefMut, AsRef, AsMut, Borrow, BorrowMut, From , Into, ToOwned

  • traits can let you break/bend rust's rules. they can also let you use them properly, depending on how you implement them or derive them

  • eg: customize how rust drops values of your type by implementing Drop

  • Copy: can only do if you're doing shallow copy. no OS handles or anything exotic .

  • (other individual ones reviewed are good example, but not note-worthy here. look up the docs.)

Chapter 14: Closure

  • closure: anonymous function expression

  • capture: use data that belongs to enclosing function by passing it in. eg: |x| println!(x)

  • borrow, or steal: borrow automatically by reference, steal by moving with move keyword

  • eg: move |x| println!(x)

  • can do same things with closures that you do with other expressions, but they don't have the same types as functions

  • "[all closures have their own type because they may contain data... so code that works with closures usually needs to be generic]"

  • Fn plain closure: call multiple times without restriction

  • FnOnce ensures called once

  • FnMut contains mutable data or mut references. not safe across threads.

  • callback: function provided by the user. in Rust these are usually done as closures, usually with lifetimes

Chapter 15: Iterators

  • iterator: value that produces a sequence of values

  • Rust ones are "flexible, expressive, efficient"

  • any value that implements the std::iter::Iterator trait, and/or IntoIterator

  • code that receives the items is a consumer

  • most collections types provide methods to produce: 1) shared reference, 2) mutable reference, 3) value

  • most have drain: takes mutable reference, returns iterator that passes ownership of each element to consumer

  • adapters: consume one iterator, producing another (eg: map and filter)

  • adapters are zero-overhead abstraction - cost nothing

  • (too many examples to list here)

  • many collections implement the extend trait, allowing one iterable to be combined with another

Chapter 16: Collections

  • collections: generic types for storing data in memory

  • mostly use moves to avoid deep-copying values

  • don't have invalidation errors: can't change collection while operating on it because of Rusts borrowing mechanisms

  • access by reference, or access by copy

  • Rust lets you borrow mutable references to two or more parts of an array, slice, or vector. safe because Rust dives them into non-overlapping regions.

  • two slices are equal if they're the same length, and their corresponding elements are equal

  • notable: Vec<T>, VecDeque<T>, LinkedList<T>, BinaryHeap<T>, HashMap<K, V>, BTreeMap<K, V>, HashSet<T> , BTreeSet<T>,

  • Hash, and Hasher work via buddy-trait; "pluggable hashing"

Chapter 17: Strings and Text

  • String and str are well-formed UTF-8 sequences

  • ASCII subset of UTF-8

  • char is 32-bit value holding a Unicode code point

  • String is just a wrapper around Vec

  • String supports operator overloading with the Add and AddAssign traits

  • can use patterns to search, manipulate text

  • converting other types to human-readable formats through Display trait, then format! macro can format without instruction

  • (side note: use Cow when you may or may not need to modify text that is borrowed)

  • string templates must be constant (or be created through macros) in order to be type checked at compile time

  • (see text formatting online for more details about all formats, arguments, etc.)

  • debug: {:?}, pretty-print: {:?#}

  • rust's regex uses matches and patterns, so it's safe for untrusted expressions/text

  • regular expression compilation is expensive; do once, keep out of loops

Chapter 18: Input and Output

  • I/O organized around Read, BufRead, Write

  • Reader -> values that you can read bytes from

  • Writer -> values you can write bytes to.

  • UTF-8 is the de facto standard in most Rust code

  • BufRead basically same as Read but uses chunks, more configurable

  • readers and writers are closed automatically when dropped - hold them if you want them open

  • File API uses builder-like pattern to open, create reader, and read

  • other reader + writer types: io::stdin, io::stdout, io::stderr

  • (a lot of Path, OS, File, Dir stuff. none of it particularly unique to rust. lookup docs.)

Chapter 19: Concurrency

  • "[Rust offers a better concurrency model, by not forcing all programs to adopt single style. Unwritten rules are written down, enforced by compiler.]"

  • fork-join parallelism: simple, avoids bottlenecks, straightforward, easy to reason about

  • std::thread::spawn new OS thread, just like other languages

  • move key, or workload via move in spawn: spawn(move || do_process(unit))

  • moves are cheap; ok to do.

  • join back together std::thread::Result that has err if child panicked

  • since panics are per-thread; this is ok.

  • rust checks closure of spawn: "[has no way of knowing how long child will run, assumes forever. requires lifetime.]"

  • can have child thread access across thread with Arc<T> ("Atomic Ref. Counter")

  • other libraries use scoped threads, worker pools, work-stealing to push out more efficiency

  • channel: one-way conduit for sending values from one thread to another. sorta like Go.

  • channels are thread-safe queues

  • use .send() and .recv(): fail if the other end of channel has been dropped

  • use move to pass channel to threads. channels are thread safe because they're for threads

  • usually loop on the receiver; exit when sender drops

  • std::sync::mpsc for multi-producer, multi-consumer

  • implement Sender and Receiver

  • std::sync::mpmc::sync_channel -> lets you do back pressure so the producers don't overwhelm consumers

  • types that implement Send are safe to pass by value to another thread

  • types that implement Sync are safe to pass by non-mut reference to another thread

  • struct or enum is Send if its fields are Send, same for Sync

  • mutex -> lock forces threads to take turns; one thread has access at a time

  • "support programming w/ invariants: rules that protect data by construction"

  • commonly Arc for sharing things across threads, Mutex for mutable data shared across threads

  • mut and Mutex: "mut means exclusive access, non-mut is shared access"

  • "[Mutex provides exclusive (mut) access, even though some threads might have shared (non-mut) access.]"

  • Rust can't protect you from being dumb; can't stop deadlock

  • if a thread panics while holding mutex, it's marked as "poisoned", attempts to lock will get error

  • RWLock like mutex but two locks; one for reading, one for writing: "one writer, or many readers, not both"

  • std::sync::Convar conditional variables for waiting, notifying, when threads need something

  • std::async::Atomic atomic types for lock-free concurrent programming

  • when it comes to global state: don't do it: "[tends to make parts of a program more tightly coupled]"

  • can use static keyword

  • can use lazy_static macro, usually with mutex

Chapter 20: Macros

  • let you extend the language via pseudo-code-gen

  • each macro call is "expanded" - replace with Rust code

  • matching patterns to templates

  • usually use macro_rules! but you could use other ways, or other macros

  • in Rust compilation process, it expands macros before looking at rest of program

  • macro patterns are basically regular expressions; use tokens

  • hard to debug because of expansion, but use rustc to look at code after expansion, use log_syntax! to print macro args

  • rust has hygienic macros; auto-names variables during expansion so you don't need to worry about collisions, naming.

  • any identifiers you need inside a macro should be passed in as parameters

  • macros always visible to child modules

  • macros visible to parents through use of "#[export_macro]" to export, or "#[macro_use]" on module import

  • exported macros shouldn't rely on anything in scope; macros should use absolute path names to anything they use

  • syntax errors in macros are fatal, only happen when trying to match fragments. avoid by putting more specific rules first

Chapter 21: Unsafe Code

  • unsafe code lets you tell Rust to trust you on this one.

  • use unsafe as keyword, us in fn or block

  • can use raw pointers and methods to allow unconstrained access to memory, access mutable static variables, use foreign function interface

    1. bugs that occur before unsafe block can break contracts, 2) consequences might occur outside unsafe block
  • good set of rules for Rust programs:

    • must not read uninitialized memory
    • must not create invalid primitive values
    • no references outlive referents shared access is read only, mutable access is exclusive
    • must not dereference null, or dangling pointers
    • must not use pointers to access memory outside allocation of association
    • free of data races
    • must not unwind across a call made from another language
    • comply with contracts from std library functions
  • raw pointer unconstrained pointer - Rust can't tell if you're using them safely. deref only in unsafe block

  • two types of raw pointers: *mut T, *const T

  • . operator doesn't auto-deref. have to be explicit with (*thing).field

  • comparison operators use addresses; only equal if they share same address location

  • "[complete, exact contract for raw pointers is not easily state, and might change]"

  • null raw pointer is a zero address

  • foreign function interface -> lets rust call functions written in C, or C++

  • extern block: declares functions or variables defined in some other library that Rust is linked with

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