rust - Struct that owns some data and a reference to the data -


this question has answer here:

construction of object allocates data needed lifetime of object, creates object needs keep references data:

pub fn new() -> obj {     let data = compute();      obj {         original: data,         processed: anotherobj {             reference: &data         }     } }

is possible express in rust's terms?

here i'd obj, anotherobj , data have same lifetime, , of course outlive new() call.

a raw design of structs based on requirements might this:

struct anotherobj<'a> {     original: &'a vec<i8>, // let's agree on vec<i8> "data" type. }  struct obj<'a> {     original: vec<i8>,         // <-------------------+     processed: anotherobj<'a>, // should point here --+ }

however it's tricky working (personally, wasn't able to) because want 'a in anotherobj<'a> lifetime of original. must supply lifetime obj<'a> , have specify obj<'tbc> 'tbc lifetime of obj created.

i suggest following alternatives:

1. make anotherobj own original

why not? obj own anotherobj, can still have access original nested child:

pub struct anotherobj {     original: vec<i8>, }  pub struct obj {     processed: anotherobj, }  pub fn new() -> obj {     let data = vec![1,2,3];      obj {         processed: anotherobj {             original: data,             // ...         }     } }  // access obj.processed.original, can create getter `fn original(&self)`

2. shared pointer design

straightforward use of refcounted pointers:

use std::rc::rc;  pub struct anotherobj {     original: rc<vec<i8>>, }  pub struct obj {     original: rc<vec<i8>>,     processed: anotherobj, }  pub fn new() -> obj {     let data = rc::new(vec![1,2,3]);      obj {         original: data.clone(),         processed: anotherobj {             original: data.clone(),         }     } }

3. raw pointers

options 1. , 2. bring peace of mind of safe rust gods, therefore don't recommend third option. still post here completeness. note: compiles, never tested @ runtime, may bite. there's safe code below you'll have go in unsafe land when want dereference raw pointer.

use std::ptr;  pub struct anotherobj {     original: *mut vec<i8>, }  pub struct obj {     original: vec<i8>,     processed: anotherobj, }  pub fn new() -> obj {     let data = vec![1,2,3];      let mut obj = obj {         original: data,         processed: anotherobj {             original: ptr::null_mut(),         }     };     obj.processed.original = &mut obj.original *mut vec<i8>;      obj }

Comments

Post a Comment

Popular posts from this blog

c# - Validate object ID from GET to POST -

i have method allows user access comment have made on site. have post method lets them update comment. my normal solution send entire comment model through, let them update it, update on database when post back. involve sending commentid through in hiddenfor , can manipulated. how can verify commentid sent in get method same i'm getting in post , not able alter comment wish? how can verify commentid sent in method same i'm getting in post? basically have validate following things in post - user logged-in user. authenticated users post comments. commentid in post , should valid commentid , should present in database. userid associated logged-in user should same userid associated comment . comment should contain userid column, can check @ time of update. to make sure update happens comment has been sent in get - hold commentid in session , in post action compare commentid value in session .
Read more

node.js - Custom Model Validator SailsJS -

when using custom model validator checks record within model. return within spread doesn't seem end control flow. //post.js model /** * custom validator **/ types: { isuservalid: function(user_id) { var promise = require('bluebird'); promise.all([ user.findone({id: user_id}) ]) .spread(function(user) { console.log(user); if (user === null || user === undefined) { console.log('failed'); return false; }else{ console.log('passed'); return true; } }); } }, my response standard validation failed response. { "error": "e_validation", "status": 400, "summary": "1 attribute invalid", "model": "post", "invalidattributes": { "owner": [ { "rule": "isuservalid", ...
Read more

php - Find a regex to take part of Email -

i have following emails need extract part from: bestellnummer xxx: 1 von xxx, 1er pack ------------- anfang der nachricht ------------- foo bar baz foo bar baz // <<<<< need text here ------------- ende der nachricht ------------- ------------- anfang der nachricht ------------- foo bar baz foo bar baz ------------- ende der nachricht ------------- there 0 unlimited occurences of ------------- anfang der nachricht ------------- ------------- ende der nachricht ------------- and i'm able extract first part regex: $re = "/------------- .*? -------------.?(.*?).?------------- .*? -------------/s"; but, i'm quite new on learning regex, i'm pretty sure there must better regex extract part (foo bar baz foo bar baz) of text between ------------- anfang der nachricht ------------- ------------- ende der nachricht ------------- as can in different languages, i'm using .? to match between hyphens. i...
Read more