-mod word_utils {
- pub fn first_word(s: &str) -> &str {
- for (i, &item) in s.as_bytes().iter().enumerate() {
- if item == b' ' {
- return &s[..i];
- }
- }
-
- s
- }
-
- pub fn second_word(s: &str) -> Option<&str> {
- for (i, &item) in s.as_bytes().iter().enumerate() {
- if item == b' ' {
- return Some(first_word(&s[(i + 1)..]));
- }
- }
+mod word_utils;
- return None;
- }
-}
+use std::collections::HashMap;
+use std::io::{prelude::*, ErrorKind};
+use std::fs::{self, File};
use word_utils::{first_word, second_word};
-fn main() {
+fn test_strings() {
let s = String::from("Hello world");
println!("first word: '{}'", first_word(&s));
println!("second word: '{}'", second_word(&s).unwrap());
None => println!("match: second word of '{}' does not exist", s2),
}
}
+
+fn test_vectors() {
+ let v1 = vec![1, 2, 3];
+ println!("statically initialized vector: {:?}", v1);
+
+ let mut v2: Vec<String> = Vec::new();
+ v2.push("Hello".to_string());
+ v2.push(String::from("world"));
+ println!("dynamically built vector: {:?}", v2);
+ println!("first element: {}", v2[0]);
+ for el in &mut v2 {
+ *el += "xx";
+ }
+ for el in &v2 {
+ println!("{}", el);
+ }
+}
+
+fn test_hashmaps() {
+ let mut scores = HashMap::new();
+ scores.insert("john", 10);
+ scores.insert("mary", 20);
+
+ println!("scores: {:?}", scores);
+
+ // hash map with .collect()
+ let persons = vec![("homer", 42), ("marge", 30)];
+ let collect_scores: HashMap<_, _> = persons.into_iter().collect();
+ println!("collect_scores: {:?}", collect_scores);
+
+ for (p, s) in &collect_scores {
+ println!("person {}: score {}", p, s);
+ }
+
+ println!("john's score: {}", scores.get("john").unwrap());
+ println!("jake's score: {}", scores.get("jake").unwrap_or(&-1));
+
+ // double scores
+ for (_, v) in scores.iter_mut() {
+ *v *= 2;
+ }
+ println!("scores after doubling: {:?}", scores);
+
+ // double scores of immutable hashmap (rebuild it)
+ let collect_scores: HashMap<_, _> = collect_scores.iter()
+ .map(|(k, v)| (k, 2 * v))
+ .collect();
+ println!("collect_scores after rebuilding with doubling: {:?}", collect_scores);
+}
+
+fn read_file(path: &str) -> Result<String, std::io::Error> {
+ let mut s = String::new();
+ File::open(path)?
+ .read_to_string(&mut s)?;
+ Ok(s)
+}
+
+fn test_files() {
+ if let Ok(mut f) = File::open("Cargo.toml") {
+ let mut contents = String::new();
+ match f.read_to_string(&mut contents) {
+ Ok(len) => println!("successfully opened Cargo.toml: {:?}, contents {} bytes:\n{}\n----------", f, len, contents),
+ Err(e) => panic!("could not read file: {:?}", e)
+ }
+ } else {
+ println!("could not open Cargo.toml");
+ }
+
+ // alternative form, more specific error checking
+ let mut f = File::open("Cargo.toml").unwrap_or_else(|e| {
+ if e.kind() == ErrorKind::NotFound {
+ println!("Cargo.toml not found, falling back to /dev/null");
+ // need to return a File
+ File::open("/dev/null").unwrap()
+ } else {
+ panic!("Could not open Cargo.toml: {:?}", e);
+ }
+ });
+ let mut contents = String::new();
+ let len = f.read_to_string(&mut contents).unwrap_or_else(|e| {
+ panic!("Could not read file: {:?}", e);
+ });
+ println!("successfully opened Cargo.toml with unwrap_or_else: {:?}, contents {} bytes:\n{}\n----------", f, len, contents);
+
+ // using the '?' operator
+ match read_file("Cargo.toml") {
+ Ok(s) => println!("Cargo.toml contents:\n{}\n-------------", s),
+ Err(e) => println!("Could not open Cargo.toml: {:?}", e)
+ }
+
+ // using std API
+ match fs::read_to_string("Cargo.toml") {
+ Ok(s) => println!("Cargo.toml contents:\n{}\n-------------", s),
+ Err(e) => println!("Could not open Cargo.toml: {:?}", e)
+ }
+}
+
+// needs Copy trait, good for simple types
+fn largest<T: PartialOrd + Copy>(list: &[T]) -> T {
+ let mut result = list[0];
+ for &i in list {
+ if i > result {
+ result = i;
+ }
+ }
+ result
+}
+
+// expensive for large strings, don't use that
+fn largest_clone<T: PartialOrd + Clone>(list: &[T]) -> T {
+ let mut result = list[0].clone();
+ for i in list {
+ if *i > result {
+ result = i.clone();
+ }
+ }
+ result
+}
+
+// good for everything, but more expensive for simple types
+fn largest_ref<T: PartialOrd>(list: &[T]) -> &T {
+ let mut result = &list[0];
+ for i in list {
+ if i > result {
+ result = i;
+ }
+ }
+ result
+}
+
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+ if x.len() > y.len() {
+ x
+ } else {
+ y
+ }
+}
+
+fn test_generics() {
+ let num_list = vec![3, 42, -7, 100, 0];
+ println!("largest number: {}", largest(&num_list));
+ println!("num_list: {:?}", num_list);
+
+ let char_list = vec!['a', 'y', 'q', 'm'];
+ println!("largest char: {}", largest(&char_list));
+
+ let str_list = vec!["hello", "world", "blue", "planet"];
+ println!("largest str: {}", largest(&str_list));
+ println!("str_list: {:?}", str_list);
+
+ let string_list = vec!["aaaa".to_string(), "xxxxx".to_string(), "ffff".to_string()];
+ println!("largest string (with cloning): {}", largest_clone(&string_list));
+ println!("largest string (with ref): {}", largest_ref(&string_list));
+ println!("string_list: {:?}", string_list);
+
+ let s1 = String::from("abcd");
+ let l;
+ {
+ let s2 = "efghi";
+ l = longest(&s1, s2);
+ }
+ println!("longest string: {}", l);
+}
+
+fn main() {
+ test_strings();
+ test_vectors();
+ test_hashmaps();
+ test_files();
+ test_generics();
+}
projects / learn-rust.git / blobdiff