Parsing text file lines into numbers using std::iter::Iterator map -

-

i'm trying read , parse text file in rust. each line signed integer. i'm able using for line in lines iteration i'm unable iter().map(|l| ...) one-liner. i'm getting a

expected `&core::result::result<collections::string::string, std::io::error::error>`, found `core::result::result<_, _>`

when try pattern match ok(s) => match s.parse() i'm unable bottom of doing wrong. whole example below. code on bottom code producing error.

can tell doing wrong?

use std::error::error; use std::fs::file; use std::io::bufreader; use std::io::prelude::*; use std::path::path;  fn main() {     // create path desired file     let path = path::new("input/numbers.txt");     let display = path.display();      // open path in read-only mode, returns `io::result<file>`     let file = match file::open(&path) {         // `description` method of `io::error` returns string describes error         err(why) => panic!("couldn't open {}: {}", display, error::description(&why)),         ok(file) => file,     };      // collect lines vector     let reader = bufreader::new(file);     let lines: vec<_> = reader.lines().collect();      // works.     let mut nums = vec![];            l in lines {         println!("{:?}", l);         let num = match l {             ok(s) => match s.parse() {                  ok(i) => i,                 err(_) => 0             },             err(_) => 0         };         nums.push(num);     }      // doesn't work!            let nums: vec<i64> = lines.iter().map(|l| match l {         ok(s) => match s.parse() {             ok(i) => i,             err(_) => 0         },         err(_) => 0     }); }

let's @ complete error message, points error us:

<anon>:5:9: 5:14 error: mismatched types:  expected `&core::result::result<&str, ()>`,     found `core::result::result<_, _>` (expected &-ptr,     found enum `core::result::result`) [e0308] <anon>:5         ok(s) => match s.parse() {                  ^~~~~

the compiler expecting &result, found result, , issue ok(s) pattern. type of l reference result because using iter - returns an iterator of references items in vector.

the shortest fix add & pattern match closure variable:

fn main() {     let lines: vec<result<_, ()>> = vec![ok("1"), ok("3"), ok("5")];      // here                                v      let nums: vec<i64> = lines.iter().map(|&l| match l {         ok(s) => match s.parse() {             ok(i) => i,             err(_) => 0         },         err(_) => 0     }).collect();      println!("{:?}", nums) }

i had add collect go vec.

the other change make consume input vector using into_iter , iterate on each value in vector:

// here                    v~~~~ let nums: vec<i64> = lines.into_iter().map(|l| match l {

and measure, use ok, and_then, , unwrap_or same thing bit more succinctly:

let nums: vec<i64> = lines.into_iter().map(|l| {     l.ok().and_then(|s| s.parse().ok()).unwrap_or(0) }).collect();

Comments

Post a Comment

Popular posts from this blog

python - TypeError: start must be a integer -

-
i trying draw 5 turtles, getting typeerror on line 25. here code: import turtle wn = turtle.screen() redrose = turtle.turtle() color = input("what background color be?") fillcolor_f = input("what color of rose be?") redrose.hideturtle() redrose.speed(30) redrose.penup() redrose.left(180) redrose.forward(175) redrose.right(90) redrose.forward(30) redrose.right(90) redrose.pendown() def drawrose(red): redrose.color("pink") redrose.fillcolor(fillcolor_f) redrose.fill(true) in range(red): redrose.forward(i) redrose.right(49) in range(5): drawrose(redrose) redrose.penup() redrose.forward(350) redrose.right(144) redrose.pendown() redrose.fill(false) drawrose(50) wn.bgcolor(color) i trying draw 5 roses, produces errors. doing in interactivepython.org. you recursively calling drawrose wrong parameter. on line 23 ( for in range(red): ) expect red integer...
Read more

c# - DevExpress RepositoryItemComboBox BackColor property ignored -

-
i have following code almost works properly; private void cbstatus_drawitem(object sender, listboxdrawitemeventargs e) { string item = e.item string; if (item != null) { switch (item) { case "1": e.appearance.forecolor = color.green; e.appearance.backcolor = color.green; break; case "2": e.appearance.forecolor = color.orange; e.appearance.backcolor = color.orange; break; case "3": e.appearance.forecolor = color.red; e.appearance.backcolor = color.red; break; } } } when dropdown shown, items forecolor correct, backcolor remains whatever backcolor of theme is; i.e. if i've got set dark theme, backcolor dark, cells in gridview, rather being green/orange/red. i've tried setting e.appearance.options.usebackcolor trying set e....
Read more

django - Creating multiple model instances in DRF3 -

-
1) create multiple model instances 1 api call, asked here: how create multiple model instances django rest framework? tried solution named in link, no success. i trying upload multiple files in 1 api call. result: files uploaded (only once overwrote perform_create) 1 instance created (if send 2 files, latter created instance). my code: class fileuploadserializer(serializers.modelserializer): def __init__(self, *args, **kwargs): many = kwargs.pop('many', true) super(fileuploadserializer, self).__init__(many=many, *args, **kwargs) class meta: model = fileupload read_only_fields = ('created', 'datafile', 'owner') class fileuploadviewset(viewsets.modelviewset): queryset = fileupload.objects.all() serializer_class = fileuploadserializer parser_classes = (multipartparser, formparser, ) def perform_create(self, serializer): file_list = self.request.data.getlist('file') ...
Read more