rust/notes

const is a thing
const convention is all upper with _
const evaluation info: https://doc.rust-lang.org/reference/const_eval.html

you can add arbitray scopes to modify local variables or for other purposes!
	{
	some random shit;
	}

https://doc.rust-lang.org/book/ch03-02-data-types.html

scalars:
	ints
	floats
	bools
	chars
integer types:
	8-bit	i8	u8
	16-bit	i16	u16
	32-bit	i32	u32
	64-bit	i64	u64
	128-bit	i128	u128
	arch	isize	usize

number literals
decimal	1_024
hex	0xff
oct	0o77
binary	0b1100_1011_0100_0001
byte	b'E'

release builds have no overflow wrap checking
don't rely on this behavior

explicitly use
`wrapping_*` methods to do this
	such as wrapping_add
Return the None value if there is overflow with the checked_* methods
Return the value and a boolean indicating whether there was overflow with the overflowing_* methods

wtf is this:
  Saturate at the value’s minimum or maximum values with saturating_* methods

there are f32 and f64 floats. f64 is default cause they are about the same speed

normal math operators
int division is floor
remainder % exists

all operators:
https://doc.rust-lang.org/book/appendix-02-operators.html


type annotation:

let var: type = val;

Rust’s char type is four bytes in size and represents a Unicode Scalar Value

Compound types

  primitive compound types:
  	tuples
	arrays

Tuples:
	fixed length combo of types
	type is ()

	pulling out the elements of a tuple into individual variables is called destructuring

Arrays:
	fixed type fixed length
	[]

	init:
		let a: [1, 2, 3];
		let a: [3, 0]; // set every element to same value
	reference:
		let first = a[0];
	they are allocated on stack

https://doc.rust-lang.org/book/ch03-03-how-functions-work.html

all function parameters must be annotated
functions consist of statements and expressions
statements perform an action and have no return value
expressions do return something

a scope block is an expression
expressions do not end with a ";", if you add a ";" it will be statement
return is explicit if the last statement in a function is an expression

https://doc.rust-lang.org/book/ch03-04-comments.html
comments

// is a comment
/* is also a comment
b*/

for some reason the doc didn't mention the second type..


https://doc.rust-lang.org/book/ch03-05-control-flow.html
control flow

there is `if``

block of code within the "if" are _arms_.
just like the match

if must recieve a bool
no bad python
if num {}

if (thing) {
    else if (other thing) {
}   else if (yat) {
}   else {
}

use `match` for too many else ifs

if is an expression!

you can loop with `loop`
loop is an expression!

break can return a value (not for for loops though they are a statement)
break can select nest level with 'label

thats called a loop label

while loop exists
for loop exists

syntax: for x in y {}

(start..end) is a Range
(1..4).rev() is a thing


https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html?search=
ownership

stack - lifo in order memory storage, stack of PLATES
	pushing / popping
	all data stored here must have a FIXED size

heap - rando shit goes here
	allocating / deallocating
	pointer to data structure goes on the stack, the actual data goes on the heap

each value in Rust has an _owner_
there can be only one owner at a time
when the owner goes out of scope, the value goes out of scope

a string has 3 parts

name | val
-----------
ptr  |  ------> index | val
len  |  5 |     -------------
cap  |  5 |     | 0   | 'h' |
-----------     | 1   | 'e' |


string2 = string1;
create a new string data structure
have the pointer point to the same data as string1

invalid:

s2 = s1;
println!("{s1}");

there can't be two pointers to the same value!

shallow copy is a move because the first pointer is invalidated

clone is "deep copy"

s2 = s1.clone();

stack based vars don't need to clone, they `copy`, it's automatic

drop is called to return memory from the heap when it's owner goes out of scope

any type that implements the copy trait will auto copy.
a type can not implement copy and drop...

tuples will copy if all of their types support it, it will not if any one of them does not

a function can take an immutable heap mounted variable and "recast" it is mutable

https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html
references

rust has a method to let a function use a variable without moving / reassigning
ownership: references

& is a reference
* is a dereference

pass a reference to avoid _moving_ the value
references are immutable by default

&mut var // makes a mutable reference

there can be one or multiple r/o references or only one mutable reference at a time

https://doc.rust-lang.org/book/ch04-03-slices.html
slices

reference to a contiguous sequence of elements

enumerate returns a tuple with counter and reference to thing (counter, &thing)

slice is a pointer to a string, with a length

let s = String::from("a a a a");
slice = &s[0..2];

you can drop the first number if it's zero: let slice = &s[..2];
or the last number if it's the end of the string: let slice = &s[4..];
or both numbers to slice the whole thing: let slice = &s[..];

you can not create a slice that starts or ends within multibyte unicode parts

String: a heap allocated vector of bytes that is stored on the heap. It is potentially mutable.
&str: an immutable borrowed string slice.

let s = "string"; // string literal (it's a slice)