Questions[rust]

I was experimenting with strings and the library std::io, so I tried to make a program that would print all the characters of a string to the screen one by one:

use std::io;

fn main() {
    
let mut expresion = String::new();

    io::stdin()
        .read_line(&mut expresion)
        .expect("No se pudo leer la linea");

    if expresion.trim() == "exit" {
        print!("el plan ha fallado con exito");
    }

    for i in 0..expresion.len(){
        println!("{}", &expresion[i-1..i] );
    }
}

I don't get any syntax errors, the program compiles without problem, but at runtime, I get the following error:

"thread 'main' panicked at 'attempt to subtract with overflow', src/main.rs:16:35"

How could I make a hash in vector format, with a vector of bytes? (without crypto-hash library)

I have a u8 vector with bytes and I would need a u8 vector with sha256 .

use sha2::{Sha256, Digest};

pub trait Hashable {
    fn bytes (&self) -> Vec<u8>;

    /// NEED TO IMPLEMENT THE HASH
    fn hash (&self) -> Vec<u8>{
        let mut hasher = Sha256::new();
        hasher.update(&self.bytes);
        let result = hasher.finalize();
        println!("{:?}", result);
    }
}

Rust has a feature that allows you to branch the way you compare objects through the and traits .PartialEqEq

Deducing from the documentation, the only difference between the two would be that it Eqadds the reflexive property to the formula.

But then, are there cases of objects that implement PartialEqwith custom code and that require Eq?

That is, if creating my own implementation of PartialEqto compare both objects, in what case would it be advisable and even mandatory to use Eq?

#[derive(PartialEq, Eq)]
enum Color {
    Red,
    Blue,
}

#[derive(PartialEq, Eq)]
enum Category {
    Hatchback,
    Truck,
}

struct Car {
    color: Color,
    category: Category,
}

impl PartialEq for Car {
    fn eq(&self, other: &Self) -> bool {
        self.category == other.category
    }
}


fn main() {
    let my_hatch = Car {
        color: Color::Blue,
        category: Category::Hatchback,
    };
    
    let my_truck = Car {
        color: Color::Red,
        category: Category::Truck,
    };
    
    println!("Are those two cars equals? {}", my_hatch == my_truck);
}

I'm just starting out with Rust and trying to program a list with pure pointers.

The code I have so far is the following:

struct Lista<T>{
    root: *mut NodoLista<T>,
    nodos: u32,
}

pub struct NodoLista<T>{
    pub value: T,
    pub child: *mut NodeLista<T>,
}

impl<T> NodoLista<T>{
    
    fn new(value:T)->NodoLista<T>{
        NodoLista::<T>{value, child:None}
    }

}

impl<T> Lista<T>{

    fn new(){
        Lista::<T>{root:None, nodos: 0};
    }

    fn len(self)->u32{
        return self.nodos;
    }
        
}

fn main(){

    let lista = Lista::new();

    println!("Tamaño de la lista {}", lista.len());

}

When compiling it returns the following error:

error[E0412]: cannot find type 'NodeLista' in this scope

help: a struct with a similar name exists: 'NodoLista'

How could I solve that problem?

I am creating a code to be able to print text on the screen with the rust macro (asm!) and this is the code:

fn printmsg(string: &str) {
    let length: usize = string.len();
    unsafe {
        asm!("syscall" :: "{rax}"(1), "{rdi}"(1), "{rsi}"(&string), "{rdx}"(length));
    }
}

fn main() {
    let s = "hello world!";
    printmsg(s);
}

When I run the code it prints random letters...

How do I get it to print "hello world!" and not something else?