From 369ae2e63d06de6fee36aeebfd1ff3e8bcdfa25a Mon Sep 17 00:00:00 2001 From: liv Date: Mon, 12 Jun 2023 12:07:18 +0200 Subject: [PATCH] feat(move_semantics2): rewrite hint --- exercises/move_semantics/move_semantics2.rs | 10 +++---- info.toml | 29 +++++++++++---------- 2 files changed, 19 insertions(+), 20 deletions(-) diff --git a/exercises/move_semantics/move_semantics2.rs b/exercises/move_semantics/move_semantics2.rs index 93bb82e..66ddb4c 100644 --- a/exercises/move_semantics/move_semantics2.rs +++ b/exercises/move_semantics/move_semantics2.rs @@ -2,23 +2,21 @@ // Execute `rustlings hint move_semantics2` or use the `hint` watch subcommand for a hint. // Expected output: -// vec0 has length 3 content `[22, 44, 66]` -// vec1 has length 4 content `[22, 44, 66, 88]` +// vec0 has length 3, with contents `[22, 44, 66]` +// vec1 has length 4, with contents `[22, 44, 66, 88]` // I AM NOT DONE fn main() { let vec0 = Vec::new(); - // Do not move the following line! let mut vec1 = fill_vec(vec0); - // Do not change the following line! - println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0); + println!("{} has length {}, with contents: `{:?}`", "vec0", vec0.len(), vec0); vec1.push(88); - println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1); + println!("{} has length {}, with contents `{:?}`", "vec1", vec1.len(), vec1); } fn fill_vec(vec: Vec) -> Vec { diff --git a/info.toml b/info.toml index 2add5f0..8febf41 100644 --- a/info.toml +++ b/info.toml @@ -287,23 +287,24 @@ Also: Try accessing `vec0` after having called `fill_vec()`. See what happens!"" [[exercises]] name = "move_semantics2" path = "exercises/move_semantics/move_semantics2.rs" -mode = "compile" +mode = "test" hint = """ -So, `vec0` is passed into the `fill_vec` function as an argument. In Rust, -when an argument is passed to a function and it's not explicitly returned, -you can't use the original variable anymore. We call this "moving" a variable. -Variables that are moved into a function (or block scope) and aren't explicitly -returned get "dropped" at the end of that function. This is also what happens here. -There's a few ways to fix this, try them all if you want: -1. Make another, separate version of the data that's in `vec0` and pass that +When running this exercise for the first time, you'll notice an error about +"borrow of moved value". In Rust, when an argument is passed to a function and +it's not explicitly returned, you can't use the original variable anymore. +We call this "moving" a variable. When we pass `vec0` into `fill_vec`, it's being +"moved" into `vec1`, meaning we can't access `vec0` anymore after the fact. +Rust provides a couple of different ways to mitigate this issue, feel free to try them all: +1. You could make another, separate version of the data that's in `vec0` and pass that to `fill_vec` instead. 2. Make `fill_vec` borrow its argument instead of taking ownership of it, - and then copy the data within the function in order to return an owned - `Vec` -3. Make `fill_vec` *mutably* borrow a reference to its argument (which will need to be - mutable), modify it directly, then not return anything. Then you can get rid - of `vec1` entirely -- note that this will change what gets printed by the - first `println!`""" + and then copy the data within the function (`vec.clone()`) in order to return an owned + `Vec`. +3. Or, you could make `fill_vec` *mutably* borrow a reference to its argument (which will need to be + mutable), modify it directly, then not return anything. This means that `vec0` will change over the + course of the function, and makes `vec1` redundant (make sure to change the parameters of the `println!` + statements if you go this route) +""" [[exercises]] name = "move_semantics3"