1. Clippy gives me the warning:

Clipping rust/upload ...
warning: passing a unit value to a function
 --> rust/upload.rs:8:5
  |
8 |     Ok(Upload{}.show())
  |     ^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unit_arg
  = note: `#[warn(clippy::unit_arg)]` on by default
help: move the expression in front of the call and replace it with the unit literal `()`
  |
8 ~     Upload{}.show();
9 +     Ok(())
  |

I read the clippy explanation and the risk of my code missed ';'. Indeed, I have no ';', but I do not need them. Any other reason why my code is bad?
2. I program in Rust using C style, so Clippy corrected me. Indeed, I tried the Clippy recommendation and it is 15% faster. But why? There is the code:

use std::error::Error;
use std::time::Instant;
trait CharLen {
    fn char_len(&self) -> usize ;
}

impl CharLen for String {
    fn char_len(&self) -> usize {
        self.chars().count()
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let s = "test ΑΒΓΔΕΖΗΘ".to_string();
    let size = 1001;
    let mut children = Vec::with_capacity(size);
    for _ in 0..size {
        children.push(s.clone())
    }
    let mut tot_len = 0;
    let start = Instant::now();
    for _ in 0..1000000 {
        for idx in 1..size {
            tot_len += children[idx].char_len()
        }
    }
    let duration = start.elapsed();

    println!("DR Time elapsed: {:?} - {tot_len}", duration);
    tot_len = 0;
    let start = Instant::now();
    for _ in 0..1000000 {
        for child in children.iter().take(size).skip(1) {
            tot_len += child.char_len()
        }
    }
    let duration = start.elapsed();

    println!("Clippy Time elapsed: {:?} - {tot_len}", duration);
    Ok(())
}

Is the C style code problem that it needs to check an index boundary from both sides, and for an iterator only upper boundary?

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