feat: add lifetimes exercises

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jayber 2022-07-15 14:01:32 +02:00 committed by mokou
parent 1cc5df0e14
commit 1ef8dacaf6
5 changed files with 114 additions and 0 deletions

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# Lifetimes
Lifetimes tell the compiler how to check whether references live long
enough to be valid in any given situation. For example lifetimes say
"make sure parameter 'a' lives as long as parameter 'b' so that the return
value is valid".
They are only necessary on borrows, i.e. references,
since copied parameters or moves are owned in their scope and cannot
be referenced outside. Lifetimes mean that calling code of e.g. functions
can be checked to make sure their arguments are valid. Lifetimes are
restrictive of their callers.
## Further information
- [Validating References with Lifetimes](https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html)
- [Lifetimes (in Rust By Example)](https://doc.rust-lang.org/stable/rust-by-example/scope/lifetime.html)

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// lifetimes1.rs
//
// The Rust compiler needs to know how to check whether supplied references are
// valid, so that it can let the programmer know if a reference is at risk
// of going out of scope before it is used. Remember, references are borrows
// and do not own their own data. What if their owner goes out of scope?
//
// Execute `rustlings hint lifetimes1` or use the `hint` watch subcommand for a hint.
// I AM NOT DONE
fn longest(x: &str, y: &str) -> &str {
if x.len() > y.len() {
x
} else {
y
}
}
fn main() {
let string1 = String::from("abcd");
let string2 = "xyz";
let result = longest(string1.as_str(), string2);
println!("The longest string is {}", result);
}

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// lifetimes2.rs
//
// So if the compiler is just validating the references passed
// to the annotated parameters and the return type, what do
// we need to change?
//
// Execute `rustlings hint lifetimes2` or use the `hint` watch subcommand for a hint.
// I AM NOT DONE
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
if x.len() > y.len() {
x
} else {
y
}
}
fn main() {
let string1 = String::from("long string is long");
let result;
{
let string2 = String::from("xyz");
result = longest(string1.as_str(), string2.as_str());
}
println!("The longest string is {}", result);
}

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// lifetimes3.rs
//
// Lifetimes are also needed when structs hold references.
//
// Execute `rustlings hint lifetimes3` or use the `hint` watch subcommand for a hint.
// I AM NOT DONE
struct Book {
author: &str,
title: &str,
}
fn main() {
let name = String::from("Jill Smith");
let title = String::from("Fish Flying");
let book = Book { author: &name, title: &title };
println!("{} by {}", book.title, book.author);
}

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@ -746,6 +746,30 @@ You can call a function right where you're passing arguments to `assert!` -- so
something like `assert!(having_fun())`. If you want to check that you indeed get false, you
can negate the result of what you're doing using `!`, like `assert!(!having_fun())`."""
# LIFETIMES
[[exercises]]
name = "lifetimes1"
path = "exercises/lifetimes/lifetimes1.rs"
mode = "compile"
hint = """
Let the compiler guide you. Also take a look at the book if you need help:
https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html"""
[[exercises]]
name = "lifetimes2"
path = "exercises/lifetimes/lifetimes2.rs"
mode = "compile"
hint = """
What is the compiler checking? How could you change how long an owned variable lives?"""
[[exercises]]
name = "lifetimes3"
path = "exercises/lifetimes/lifetimes3.rs"
mode = "compile"
hint = """
If you use a lifetime annotation in a struct's fields, where else does it need to be added?"""
# STANDARD LIBRARY TYPES
[[exercises]]