trait magic

playground.rs

use rand; // 0.7.3
use rand::Rng;

fn make_a_string_with(string: &str) -> String {
    let mut s = String::new();
    s.push_str(string);

    let mut rng = rand::thread_rng();
    let r = rng.gen_range(0, 100);
    for _ in 0..r {
        s.push_str("!");
    }
    s
}

fn make_a_string_with_ref<S>(string: S) -> String
where
    S: AsRef<str>,
{
    let mut s = String::new();
    s.push_str(string.as_ref());

    let mut rng = rand::thread_rng();
    let r = rng.gen_range(0, 100);
    for _ in 0..r {
        s.push_str("!");
    }
    s
}

fn make_a_string_with_into<S>(string: S) -> String
where
    S: Into<String>,
{
    let mut s = string.into();

    let mut rng = rand::thread_rng();
    let r = rng.gen_range(0, 100);
    for _ in 0..r {
        s.push_str("!");
    }
    s
}

fn main() {
    let slice = "Hello World"; // &'static str
    let string = String::from(slice); // also slice.to_string() or slice.to_owned()
    let moved_r_string = string.clone();
    let moved_i_string = string.clone();
    let ref_string = &string;

    // how long is a piece of string
    // coercing into &str
    let s_literal = make_a_string_with("panic");
    let s_slice = make_a_string_with(slice);
    let s_string = make_a_string_with(&string); // have to reference
    let s_ref_string = make_a_string_with(ref_string);

    // matching type with trait AsRef<str>
    let r_literal = make_a_string_with_ref("panic");
    let r_slice = make_a_string_with_ref(slice);
    let r_string = make_a_string_with_ref(moved_r_string); // moves
    let r_ref_string = make_a_string_with_ref(ref_string);

    // matching type with trait Into<String>
    let i_literal = make_a_string_with_into("panic");
    let i_slice = make_a_string_with_into(slice);
    let i_string = make_a_string_with_into(moved_i_string); // moves
    let i_ref_string = make_a_string_with_into(ref_string);

    let array:[(&str, String); 12] = [
        ("panic", s_literal),
        (slice, s_slice),
        (&string, s_string),
        (ref_string, s_ref_string),
        ("panic", r_literal),
        (slice, r_slice),
        (&string, r_string),
        (ref_string, r_ref_string),
        ("panic", i_literal),
        (slice, i_slice),
        (&string, i_string),
        (ref_string, i_ref_string),
    ];

    for (o, s) in array.iter() {
        println!("len: {}, orginal:{}, string: {}", s.len(), o, s)
    }
}