2017-03-12

Error Handling #8

rust

https://doc.rust-lang.org/book/error-handling.html

Reading from stdinの手前まででビルド通った。

extern crate getopts;
extern crate rustc_serialize;
extern crate csv;

use getopts::Options;
use std::env;
use std::fs::File;
use std::path::Path;
use std::error::Error;

// This struct represents the data in each row of the CSV file.
// Type based decoding absolves us of a lot of the nitty gritty error
// handling, like parsing strings as integers or floats.
#[derive(Debug, RustcDecodable)]
struct Row {
    country: String,
    city: String,
    accent_city: String,
    region: String,

    // Not every row has data for the population, latitude or longitude!
    // So we express them as `Option` types, which admits the possibility of
    // absence. The CSV parser will fill in the correct value for us.
    population: Option<u64>,
    latitude: Option<f64>,
    longitude: Option<f64>,
}

struct PopulationCount {
    city: String,
    country: String,
    // This is no longer an `Option` because values of this type are only
    // constructed if they have a population count.
    count: u64,
}

fn print_usage(program: &str, opts: Options) {
    println!("{}", opts.usage(&format!("Usage: {} [options] <data-path> <city>", program)));
}

fn search<P: AsRef<Path>>
         (file_path: P, city: &str)
         -> Result<Vec<PopulationCount>, Box<Error>> {
    let mut found = vec![];
    let file = try!(File::open(file_path));
    let mut rdr = csv::Reader::from_reader(file);
    for row in rdr.decode::<Row>() {
        let row = try!(row);
        match row.population {
            None => { } // Skip it.
            Some(count) => if row.city == city {
                found.push(PopulationCount {
                    city: row.city,
                    country: row.country,
                    count: count,
                });
            },
        }
    }
    if found.is_empty() {
        Err(From::from("No matching cities with a population were found."))
    } else {
        Ok(found)
    }
}

fn main() {
    let args: Vec<String> = env::args().collect();
    let program = &args[0];

    let mut opts = Options::new();
    opts.optflag("h", "help", "Show this usage message.");

    let matches = match opts.parse(&args[1..]) {
        Ok(m)  => { m }
        Err(e) => { panic!(e.to_string()) }
    };

    if matches.opt_present("h") {
        print_usage(&program, opts);
        return;
    }

    let data_path = &matches.free[0];
    let city: &str = &matches.free[1];

    match search(data_path, city) {
        Ok(pops) => {
            for pop in pops {
                println!("{}, {}: {:?}", pop.city, pop.country, pop.count);
            }
        }
        Err(err) => println!("{}", err)
    }
}

2017-03-11

BLUE GIANT 10巻

comic

コンビニにおいてあるのをみかけて、つい立ち読みしちゃいました。セリフがないからこそ感じられる躍動感があります。電子書籍化するあたりでちゃんと購入しよう。

BLUE GIANT 10 (ビッグコミックススペシャル)

作者: 石塚真一
出版社/メーカー: 小学館
発売日: 2017/03/10
メディア: コミック
この商品を含むブログ (2件) を見る

2017-03-10

Error Handling #7

rust

https://doc.rust-lang.org/book/error-handling.html

Errorというtraitが存在する。

2017-03-09

Error Handling #6

rust

https://doc.rust-lang.org/book/error-handling.html

エラーの定義。

use std::io;
use std::num;

// We derive `Debug` because all types should probably derive `Debug`.
// This gives us a reasonable human readable description of `CliError` values.
#[derive(Debug)]
enum CliError {
    Io(io::Error),
    Parse(num::ParseIntError),
}

use std::fs::File;
use std::io::Read;
use std::path::Path;

fn file_double<P: AsRef<Path>>(file_path: P) -> Result<i32, CliError> {
    let mut file = try!(File::open(file_path).map_err(CliError::Io));
    let mut contents = String::new();
    try!(file.read_to_string(&mut contents).map_err(CliError::Io));
    let n: i32 = try!(contents.trim().parse().map_err(CliError::Parse));
    Ok(2 * n)
}

fn main() {
    match file_double("foobar") {
        Ok(n) => println!("{}", n),
        Err(err) => println!("Error: {:?}", err),
    }
}

$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
Error: Io(Error { repr: Os { code: 2, message: "No such file or directory" } })
$ touch foobar
$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
Error: Parse(ParseIntError { kind: Empty })
$ echo 3 > foobar
$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
6
$ echo "a" > foobar
$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
Error: Parse(ParseIntError { kind: InvalidDigit })

2017-03-08

Error Handling #5

rust

https://doc.rust-lang.org/book/error-handling.html

ファイル処理の異常処理の続き。エラーの時の処理が明示的になってきたように思う。

use std::fs::File;
use std::io::Read;
use std::path::Path;

fn file_double<P: AsRef<Path>>(file_path: P) -> Result<i32, String> {
    let mut file = match File::open(file_path) {
        Ok(file) => file,
        Err(err) => return Err(err.to_string()),
    };
    let mut contents = String::new();
    if let Err(err) = file.read_to_string(&mut contents) {
        return Err(err.to_string());
    }
    let n: i32 = match contents.trim().parse() {
        Ok(n) => n,
        Err(err) => return Err(err.to_string()),
    };
    Ok(2 * n)
}

fn main() {
    match file_double("foobar") {
        Ok(n) => println!("{}", n),
        Err(err) => println!("Error: {}", err),
    }
}

2017-03-07

Error Handling #4

rust

https://doc.rust-lang.org/book/error-handling.html

use std::fs::File;
use std::io::Read;
use std::path::Path;

fn file_double<P: AsRef<Path>>(file_path: P) -> i32 {
    let mut file = File::open(file_path).unwrap(); // error 1
    let mut contents = String::new();
    file.read_to_string(&mut contents).unwrap(); // error 2
    let n: i32 = contents.trim().parse().unwrap(); // error 3
    2 * n
}

fn main() {
    let doubled = file_double("foobar");
    println!("{}", doubled);
}

$ cargo run
   Compiling 5_7_error_handling v0.1.0 (file:///Users/miura/work/git-work/exercises/The_Rust_Programming_Language/5_7_error_handling)
    Finished debug [unoptimized + debuginfo] target(s) in 1.38 secs
     Running `target/debug/5_7_error_handling`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "No such file or directory" } }', ../src/libcore/result.rs:837
note: Run with `RUST_BACKTRACE=1` for a backtrace.
$ touch foobar
$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: Empty }', ../src/libcore/result.rs:837
note: Run with `RUST_BACKTRACE=1` for a backtrace.
$ echo 1 > foobar
(anaconda3-4.2.0) miura (master *) 5_7_error_handling $ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
2

2017-03-06

Error Handling #3

rust

https://doc.rust-lang.org/book/error-handling.html

use std::env;すると、argv.nthで引数をとれる。引数の有無でエラー判定するための方法。

use std::env;

fn ok_or<T, E>(option: Option<T>, err: E) -> Result<T, E> {
    match option {
        Some(val) => Ok(val),
        None => Err(err),
    }
}

fn double_arg(mut argv: env::Args) -> Result<i32, String> {
    argv.nth(1)
        .ok_or("Please give at least one argument".to_owned())
        .and_then(|arg| arg.parse::<i32>().map_err(|err| err.to_string()))
        .map(|n| 2 * n)
}

fn main() {
    match double_arg(env::args()) {
        Ok(n) => println!("{}", n),
        Err(err) => println!("Error: {}", err),
    }
}

$ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling`
Error: Please give at least one argument
$ cargo run a
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling a`
Error: invalid digit found in string
$ cargo run 3
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/5_7_error_handling 3`
6