feat/rust

Memory Management.md

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+# Memory Management
+
+[Stack vs. Heap quick comparison](https://stackoverflow.com/questions/79923)
+
+## Stack
+
+-   LIFO (Last in, first out) approach, with `push` and `pop` paradigm of addition and removal.
+-   All stored data has fixed sizes that are always known.
+-   Pushing to stack is faster than allocation to heap—no process is needed to locate where data could be placed.
+-   Popping from the stack is faster than accessing from the heap because no lookup process is needed.
+-   Integrated tightly into code.
+    When a function is called, values passed to the function, and local variables are pushed onto the stack.
+    When the function is complete, this data is popped off.
+
+## Heap
+
+Significantly less structured way of storing data. Anything with unknown or changeable size must be stored on the heap.
+
+High level approach to putting data on the heap:
+
+-   Request an amount of space.
+-   Memory allocator will find an empty spot that's big enough for your request.
+    -   Marked as being used.
+-   Pointer to address of memory is returned.
+    -   (This pointer can then be stored in the stack).
+-   Data with unknown size at compile time, or that may change is stored on the heap.
+
+https://www.metservice.com/publicData/rainRadar/image/Otago/120K/2024-01-03T12:36:00+13:00
+https://www.metservice.com/publicData/rainRadar/image/Otago/120K/2024-01-03T13:07:00+13:00

Rust.md

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+# Rust
+
+## Ownership
+
+[Ownership](https://doc.rust-lang.org/book/ch04-01-what-is-ownership.html) involves managing accessing, cleaning up, and tracking data stored in the heap.
+Rules of ownership:
+
+-   Each value has an owner.
+-   Only one owner allowed simultaneously.
+-   Owner goes out of scope = value is dropped.
+
+```rust
+{
+    let s = String::from("hello."); // s is valid from this point forward
+}
+```
+
+At the end of the scope, denoted by the braces, `s` is no longer valid and is deallocated from the heap, as Rust internally calls [`drop`](https://doc.rust-lang.org/std/ops/trait.Drop.html#tymethod.drop).
+This can also be seen with heap-allocated variables being duplicated (only one owner allowed).
+
+```rust
+let s1 = String::from("hello.");
+let s2 = s1;
+```
+
+In this scenario `s1` and `s2` both are values that contain a pointer to the _same address in memory_ for the heap-stored data.
+
+When `s2` is assigned, `s1` becomes invalid because if both were to go out of scope simultaneously, they will both be freed from memory simultaneously—despite pointing to only one location in memory.
+This is known as a _double free error_ and rust prevents this.
+
+Thus, Rust nearly always _shallow copies_ data, also known in Rust terms as a "move". The underlying data on the heap is not touched, only the pointer and metadata to it.
+To perform what would be called a _deep copy_ in Rust, the `clone` method exists:
+
+```rust
+let s1 = String::from("hello");
+let s2 = s1.clone();
+```
+
+Both `s1` and `s2` are valid at the end of this code example.
+
+## Strings
+
+**`String`** is a dynamic vector of bytes (`Vec<u8>`) and is heap-allocated, growable, UTF-8 encoded, and not [null-terminated](https://en.wikipedia.org/wiki/Null-terminated_string).
+It is an _owned type_ (as it owns the underlying bytes representing the string) and is frankly the easiest to understand data type here.
+It consists of a pointer to the string on the heap, its length, and its capacity.
+It can be [defined](https://doc.rust-lang.org/src/alloc/string.rs.html#365-367) at a high level as:
+
+```rust
+pub struct String {
+    vec: Vec<u8>
+}
+```
+
+(With an addition that the bytes of the `vec` are guaranteed to be valid UTF-8).
+
+**`&str`** is a _string slice_, also known as a "view into a string".
+It consists of a pointer to the string, and the string length, offering a view into a string.
+It is called a _borrowed type_, because it doesn't own the underlying data, and is immutable (and is therefore not growable).
+
+```rust
+let my_string: String = String::from("Hello!":);
+let my_string_slice: &str = &my_string;
+```
+
+The pointer can point to _either_ data on the heap, data in the compiled binary (in the case of string literals), or on the stack.
+
+The string slice is made up of two parts:
+
+-   The `str` type. This cannot be used directly because its size is not known at compile time.
+-   The reference operator (`&`). We use this to get a pointer to the bytes of the string and its length.
+
+A **string literal** is a `&str` that is stored within the compiled binary itself:
+
+```rust
+let my_string_literal = "Hello, world!"; // Type is `&str`, which is syntactic sugar for `&'static str`.
+```
+
+When declared like this, they are hardcoded into the final executable as they are known at compile-time.
+String literals have a "static lifetime", which is to say their lifetime persists for the duration of the program execution.
+
+-   [Summary comparison from StackOverflow](https://stackoverflow.com/a/24159933)
+-   [All Rust string types explained (Let's Get Rusty)](https://www.youtube.com/watch?v=CpvzeyzgQdw)
+
+## Pointers
+
+Types:
+
+-   "Reference"
+
+## `Box`
+
+`Box` data types are pointers that store data in the heap.
+
+## `dyn` keyword
+
+If instead of returning a known concrete object, a function returns a `trait`; then the size of the object cannot be known at compile-time; as even though each concrete implementation will adhere to the trait, the object size will differ.
+
+Thus, the return type is said to be "dynamic", and the `dyn` keyword is needed to prefix the trait name in the return type
+([before Edition 2021 though, this keyword could be omitted](https://doc.rust-lang.org/reference/types/trait-object.html)).
+Additionally, this will be wrapped in a `Box` to heap-allocate it.
+Thus, the return type is actually a pointer reference to memory on the heap.
+
+```rust
+fn get_random_traitable() -> Box<dyn MyTrait> {
+    // ...
+}
+```
+
+[Rust by example](https://doc.rust-lang.org/rust-by-example/trait/dyn.html) reference.
+
+## `Copy` trait
+
+## `pub(crate)` for struct members
+
+## Attributes
+
+### `derive(Debug)`
+
+## "Dynamic dispatch"
+
+## Apostrophes (related to types)
+
+## Lifetimes
+
+## Self vs self
+
+https://stackoverflow.com/questions/32304595/whats-the-difference-between-self-and-self