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| -rw-r--r-- | exercises/lifetimes/README.md | 17 | ||||
| -rw-r--r-- | exercises/lifetimes/lifetimes1.rs | 26 | ||||
| -rw-r--r-- | exercises/lifetimes/lifetimes2.rs | 27 | ||||
| -rw-r--r-- | exercises/lifetimes/lifetimes3.rs | 20 | ||||
| -rw-r--r-- | info.toml | 24 |
5 files changed, 114 insertions, 0 deletions
diff --git a/exercises/lifetimes/README.md b/exercises/lifetimes/README.md new file mode 100644 index 0000000..72befb3 --- /dev/null +++ b/exercises/lifetimes/README.md @@ -0,0 +1,17 @@ +# 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) diff --git a/exercises/lifetimes/lifetimes1.rs b/exercises/lifetimes/lifetimes1.rs new file mode 100644 index 0000000..58e995c --- /dev/null +++ b/exercises/lifetimes/lifetimes1.rs @@ -0,0 +1,26 @@ +// 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); +} diff --git a/exercises/lifetimes/lifetimes2.rs b/exercises/lifetimes/lifetimes2.rs new file mode 100644 index 0000000..c73a28a --- /dev/null +++ b/exercises/lifetimes/lifetimes2.rs @@ -0,0 +1,27 @@ +// 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); +} diff --git a/exercises/lifetimes/lifetimes3.rs b/exercises/lifetimes/lifetimes3.rs new file mode 100644 index 0000000..ea48370 --- /dev/null +++ b/exercises/lifetimes/lifetimes3.rs @@ -0,0 +1,20 @@ +// 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); +} @@ -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]] |