hello rust memory / published by https://github.com/dacr/code-examples-manager #4a8147eb-520e-4658-8250-bbcf987294e2/7e9823d761e70f00ab18ee1138ad3940e55c31dc

hello-memory.rs

#!/usr/bin/env rust-script
// summary : hello rust memory
// keywords : rust, memory, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 4a8147eb-520e-4658-8250-bbcf987294e2
// created-on : 2024-10-14T21:27:38+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : ./$file

// -------------------------------------------------------------------------------------------------

fn mem10() {
    let str0 = "truc";           // immutable string on the stack
    let str1 = String::from("Hello"); // dynamic string on the heap
    println!("mem1: str1={str1} - str1 has ownership");
    let mut str2 = str1;
    // ownership has moved str1 -> str2 / string data (pointer/len/capacity) is copied but not the content :
    str2.push_str("🚀");
    println!("mem1: str0={str0} str2={str2} - str1 has lost ownership, it is no longer accessible");
}

// -------------------------------------------------------------------------------------------------

fn mem15_capitalize(input: String) -> String {
    input.to_uppercase()  // new string is created
}

fn mem15() {
    let s1 = String::from("hello 🚀");
    let s2 = mem15_capitalize(s1); // From here s1 is no longer accessible : ownership as moved
    println!("capitalized: {s2}")
}

// -------------------------------------------------------------------------------------------------

fn mem16_identity(input: String) -> String {
    input
}

fn mem16() {
    let s1 = String::from("hello 🚀");
    let s2 = mem16_identity(s1); // s1 --movedTo-> mem16_identity --movedTo-> s2
    println!("transferred s1->s2: {s2} - s2 is s1 in fact - ownership back into s2 after the call")
}

// -------------------------------------------------------------------------------------------------

fn mem17_length(input: String) -> (String, usize) {
    let len = input.len();
    // (input, input.len()) // TO AVOID : (value moved here, value borrowed here after move) compilation error
    // 2 steps is required to avoid borrowing issue !!
    (input, len)
}

fn mem17() {
    let s1 = String::from("hello 🚀");
    let (s2, l) = mem17_length(s1); // s1 --movedTo-> mem17_length --movedTo-> s2
    println!("transferred: {s2} of len {l} - s2 is s1 in fact - ownership back into s2 after the call")
}

// -------------------------------------------------------------------------------------------------

fn mem20_capitalize(input: &String) -> String {
    // no ownership transfer for input, we just borrow the string and give it back once used
    input.to_uppercase()
}

fn mem20() {
    let s1 = String::from("hello 🚀");
    let s2 = mem20_capitalize(&s1); // ownership doesn´t move
    println!("capitalized: {s1} {s2} using a reference as parameter, creating a reference == borrowing ")
}

// -------------------------------------------------------------------------------------------------

fn mem40() {
    let s1 = String::from("hello 🚀"); // one memory zone on the heap = 1 owner only

    //let s2 = s1; // ownership is transfered!
    //println!("s1 = {}, s2 = {}", s1, s2); // COMPILE error - "hello 🚀" doesn't belong to s1 anymore

    let s3 = s1.clone();
    println!("s1 = {}, s3 = {}", s1, s3); // CAN'T COMPILE - s1 ne possède plus "hello 🚀"

    //  ⚠️ s1 has been copied into a new memory zone on the heap
}

// -------------------------------------------------------------------------------------------------
struct TrucDroppable { // By default, in DROP mode
    age: u16,
}

#[derive(Copy, Clone)]
struct TrucCopiable { // NOW configured in COPY mode
    age: u16,
}

fn mem80() {
    let tc1: TrucCopiable = TrucCopiable { age: 42 };
    let tc2 = tc1; // COPIED
    println!("mem2: tc1={} tc2={}", tc1.age, tc2.age);

    let td1: TrucDroppable = TrucDroppable { age: 42 };
    let td2 = td1; // MOVED - td1 is no longer accessible
    //println!("mem2: td1={} td2={}", td1.age, td2.age);
    println!("mem2: td2={}", td2.age);
}

// -------------------------------------------------------------------------------------------------
fn main() {
    mem10();
    mem15();
    mem16();
    mem17();
    mem20();
    mem40();
    mem80();
}