Hi Vladimir, thanks for the pointers guide, I forgot about it. I remember reading about it in the “normal” guide but didn’t really understand it. Hopefully if I read it a few times, it will sink in. :-)
Ollie On Wednesday 10 September 2014 at 17:17, Vladimir Matveev wrote: > Hi, Ollie, > > The working piece of code code: http://is.gd/dX7hzB > > First of all, try to go through the official Rust guide [1]. It is mostly > finished and it is *really* good. In particular, it explains what ownership > is and how it should be managed. > > I’ve took your `example_box.rs` as a base and modified it as follows: > 1. I’ve removed `Box`es everywhere. You shouldn’t use them unless you really > know why you need them. You can read more on boxes and other kinds of > pointers here [2]. You will need to do it anyway if you go through the guide > [1] anyway. > 2. I’ve made your functions to accept &mut Vec<Section> and &mut Section. > This is exactly what ownership is about: these functions should not take > ownership of their arguments, but they need to modify them, so &mut is the > solution. > > Apart from that your code is mostly fine. > > Hope that helps! > > [1]: http://doc.rust-lang.org/guide.html > [2]: http://doc.rust-lang.org/guide-pointers.html > > > On 10 сент. 2014 г., at 18:05, Oldřich Vetešník <oldrich.vetes...@gmail.com > (mailto:oldrich.vetes...@gmail.com)> wrote: > > > Hello, > > > > I have a problem with creating a mutable nested data structure when > > combined with functions. > > I’m lost in all those &muts, boxes and lifetimes. :-) > > > > I would like to crawl a directory looking for subdirectories and in those > > subdirectories find all images. > > So I started with a vector for holding those subdirectories. > > Then I created a struct to hold a directory path and a vector of images. > > Also a struct for the image itself. > > > > It all works in one function body but not when refactored into functions. > > I understand that when a variable is sent as an argument, the ownership is > > moved so it cannot be used after the function call. > > So I sent &-references instead but then it would yell at me that borrowed > > things are not mutable. > > So I &mut-ed it all and it would yell that lifetimes are not defined. > > So I tried to define lifetimes but then it would say that things do not > > live long enough. This is where I stopped. > > I also tried the box-way but that yells about immutable dereference. I’m > > not even sure I have those boxes right. > > > > This is the code: > > (Also available here https://gist.github.com/ollie/9c81d2a368bf7bf0831a, > > there is also a Ruby version not listed here.) > > > > > > With references and lifetimes: > > > > #[deriving(Show)] > > struct Image { > > filename: String, > > } > > > > #[deriving(Show)] > > struct Section<'a> { > > path: String, > > images: &'a mut Vec<Image>, > > } > > > > impl Image { > > fn new(filename: &str) -> Image { > > Image { > > filename: String::from_str(filename), > > } > > } > > } > > > > impl<'a> Section<'a> { > > fn new(path: &str) -> Section { > > Section { > > path: String::from_str(path), > > images: &mut Vec::new(), > > } > > } > > > > fn add_image(&mut self, image: Image) { > > self.images.push(image); > > } > > } > > > > fn read_directories(sections: &mut Vec<&mut Section>) { > > let dirs = ["./dir-a", "./dir-b"]; > > > > for dir in dirs.iter() { > > let mut section = &mut Section::new(*dir); > > read_images(section); > > sections.push(section); > > } > > } > > > > fn read_images(section: &mut Section) { > > let files = ["./image-1.png", "./image-2.png"]; > > > > for file in files.iter() { > > section.add_image(Image::new(*file)); > > } > > } > > > > fn main() { > > let mut sections = Vec::new(); > > read_directories(&mut sections); > > println!("{}", sections); > > } > > > > > > With boxes: > > > > #[deriving(Show)] > > struct Image { > > filename: String, > > } > > > > #[deriving(Show)] > > struct Section { > > path: String, > > images: Box<Vec<Image>>, > > } > > > > impl Image { > > fn new(filename: &str) -> Image { > > Image { > > filename: String::from_str(filename), > > } > > } > > } > > > > impl Section { > > fn new(path: &str) -> Section { > > Section { > > path: String::from_str(path), > > images: box Vec::new(), > > } > > } > > > > fn add_image(&mut self, image: Image) { > > self.images.push(image); > > } > > } > > > > fn read_directories(sections: Box<Vec<Box<Section>>>) { > > let dirs = ["./dir-a", "./dir-b"]; > > > > for dir in dirs.iter() { > > let mut section = box Section::new(*dir); > > read_images(section); > > sections.push(section); > > } > > } > > > > fn read_images(section: Box<Section>) { > > let files = ["./image-1.png", "./image-2.png"]; > > > > for file in files.iter() { > > section.add_image(Image::new(*file)); > > } > > } > > > > fn main() { > > let mut sections = box Vec::new(); > > read_directories(sections); > > println!("{}", sections); > > } > > > > > > All in one, no referenes and lifetimes: > > > > #[deriving(Show)] > > struct Image { > > filename: String, > > } > > > > #[deriving(Show)] > > struct Section { > > path: String, > > images: Vec<Image>, > > } > > > > impl Image { > > fn new(filename: &str) -> Image { > > Image { > > filename: String::from_str(filename), > > } > > } > > } > > > > impl Section { > > fn new(path: &str) -> Section { > > Section { > > path: String::from_str(path), > > images: Vec::new(), > > } > > } > > > > fn add_image(&mut self, image: Image) { > > self.images.push(image); > > } > > } > > > > fn main() { > > let mut sections = Vec::new(); > > let dirs = ["./dir-a", "./dir-b"]; > > > > for dir in dirs.iter() { > > let mut section = Section::new(*dir); > > let files = ["./image-1.png", "./image-2.png"]; > > > > for file in files.iter() { > > section.add_image(Image::new(*file)); > > } > > > > sections.push(section); > > } > > > > println!("{}", sections); > > > > // [ > > // Section { > > // path: ./dir-a, > > // images: [Image { filename: ./image-1.png }, Image { filename: > > ./image-2.png }] > > // }, > > // Section { > > // path: ./dir-b, > > // images: [Image { filename: ./image-1.png }, Image { filename: > > ./image-2.png }] > > // } > > // ] > > } > > > > I’ve read the tutorial, the rust-by-example site but it still feels alien > > to me. :-/ > > > > Thank you, > > Ollie > > _______________________________________________ > > Rust-dev mailing list > > Rust-dev@mozilla.org (mailto:Rust-dev@mozilla.org) > > https://mail.mozilla.org/listinfo/rust-dev > > > > _______________________________________________ Rust-dev mailing list Rust-dev@mozilla.org https://mail.mozilla.org/listinfo/rust-dev
