Iterators

[learn-rust.git] / src / main.rs

diff --git a/src/main.rs b/src/main.rs
index ff65a0611a6e7b40a0a86501a239ab657cc4156a..06d122b9c4c727f399d8273312ffcfb2a95088fd 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,14 @@
 mod word_utils;
+mod lib;
 
 use std::collections::HashMap;
+use std::io::{prelude::*, ErrorKind};
+use std::fs::{self, File};
 
+use lib::*;
 use word_utils::{first_word, second_word};
 
-fn main() {
-    // strings and functions
+fn test_strings() {
     let s = String::from("Hello world");
     println!("first word: '{}'", first_word(&s));
     println!("second word: '{}'", second_word(&s).unwrap());
@@ -17,8 +20,9 @@ fn main() {
         Some(w) => println!("match: second word of '{}' exists: {}", s2, w),
         None => println!("match: second word of '{}' does not exist", s2),
     }
+}
 
-    // vectors
+fn test_vectors() {
     let v1 = vec![1, 2, 3];
     println!("statically initialized vector: {:?}", v1);
 
@@ -33,8 +37,9 @@ fn main() {
     for el in &v2 {
         println!("{}", el);
     }
+}
 
-    // hash maps
+fn test_hashmaps() {
     let mut scores = HashMap::new();
     scores.insert("john", 10);
     scores.insert("mary", 20);
@@ -60,8 +65,136 @@ fn main() {
     println!("scores after doubling: {:?}", scores);
 
     // double scores of immutable hashmap (rebuild it)
-    let collect_scores: HashMap<_, _> = collect_scores.iter()
+    let collect_scores: HashMap<_, _> = collect_scores.into_iter()
         .map(|(k, v)| (k, 2 * v))
         .collect();
     println!("collect_scores after rebuilding with doubling: {:?}", collect_scores);
 }
+
+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)
+    }
+}
+
+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 test_closures() {
+    let mut expensive_int_result = Cacher::new(|x| {
+        println!("calculating expensive int result for {}", x);
+        2 * x
+    });
+
+    println!("1st int call for value 1: {}", expensive_int_result.value(1));
+    println!("2nd int call for value 1: {}", expensive_int_result.value(1));
+    println!("1st int call for value 2: {}", expensive_int_result.value(2));
+
+    let mut expensive_str_result = Cacher::new(|x: &str| {
+        println!("calculating expensive str result for {}", x);
+        x.len()
+    });
+
+    println!("1st int call for value abc: {}", expensive_str_result.value("abc"));
+    println!("2nd int call for value abc: {}", expensive_str_result.value("abc"));
+    println!("1st int call for value defg: {}", expensive_str_result.value("defg"));
+}
+
+fn test_iterators() {
+    let v1 = vec!["Hello", "good", "world"];
+    // implied default is .into_iter() which consumes v1
+    for s in v1.iter() {
+        println!("element: {}", s);
+    }
+    // can still use it now
+    println!("v1: {:?}", &v1);
+
+    // manual iteration
+    let mut v1_iter = v1.iter();
+    while let Some(e) = v1_iter.next() {
+        println!("while loop over iter: {}", e);
+    }
+
+    for l_element in v1.iter().filter(|x| x.contains('l')) {
+        println!("v1 element containing 'l': {}", l_element);
+    }
+
+    let v2 = vec![1, 2, 3];
+    let double_v2: Vec<_> = v2.iter().map(|x| x * 2).collect();
+    println!("doubled v2: {:?}", double_v2);
+
+    for i in v2.into_iter().map(|x| x * 3) {
+        println!("for loop triplicating v2: {}", i);
+    }
+
+    for i in Counter5::new() {
+        println!("Counter 5 value: {}", i);
+    }
+}
+
+fn main() {
+    test_strings();
+    test_vectors();
+    test_hashmaps();
+    test_files();
+    test_generics();
+    test_closures();
+    test_iterators();
+}