part 05: clarify exercise

[rust-101.git] / workspace / src / part03.rs

diff --git a/workspace/src/part03.rs b/workspace/src/part03.rs
index 8d1c8b69c3fce7bea45c73efd06983e3c419a92f..5a5327c26962be4ea044de8d74afab0cc4377bff 100644 (file)
--- a/workspace/src/part03.rs
+++ b/workspace/src/part03.rs
@@ -1 +1,71 @@
- 
+// Rust-101, Part 03: Input
+// ========================
+
+
+// I/O is provided by the module `std::io`, so we first have import that with `use`.
+// We also import the I/O *prelude*, which makes a bunch of commonly used I/O stuff
+// directly available.
+use std::io::prelude::*;
+use std::io;
+
+fn read_vec() -> Vec<i32> {
+    let mut vec: Vec<i32> = Vec::<i32>::new();
+    // The central handle to the standard input is made available by `io::stdin()`.
+    let stdin = io::stdin();
+    println!("Enter a list of numbers, one per line. End with Ctrl-D.");
+    for line in stdin.lock().lines() {
+        // Rust's type for (dynamic, growable) strings is `String`. However, our variable `line`
+        // here is not yet of that type: It has type `io::Result<String>`.
+
+        // I chose the same name (`line`) for the new variable to ensure that I will never, accidentally,
+        // access the "old" `line` again.
+        let line = line.unwrap();
+        // Now that we have our `String`, we want to make it an `i32`.
+
+        match line.trim().parse::<i32>() {
+            Ok(num) => {
+                unimplemented!()
+            },
+            // We don't care about the particular error, so we ignore it with a `_`.
+            Err(_) => {
+                unimplemented!()
+            },
+        }
+    }
+
+    vec
+}
+
+
+// For the rest of the code, we just re-use part 02 by importing it with `use`.
+use part02::{SomethingOrNothing,Something,Nothing,vec_min};
+
+// If you update your `main.rs` to use part 03, `cargo run` should now ask you for some numbers,
+// and tell you the minimum. Neat, isn't it?
+pub fn main() {
+    let vec = read_vec();
+    unimplemented!()
+}
+
+// **Exercise 03.1**: Define a trait `Print` to write a generic version of `SomethingOrNothing::print`.
+// Implement that trait for `i32`, and change the code above to use it.
+// I will again provide a skeleton for this solution. It also shows how to attach bounds to generic
+// implementations (just compare it to the `impl` block from the previous exercise).
+// You can read this as "For all types `T` satisfying the `Print` trait, I provide an implementation
+// for `SomethingOrNothing<T>`".
+// 
+// Notice that I called the function on `SomethingOrNothing` `print2` to disambiguate from the `print` defined previously.
+// 
+// *Hint*: There is a macro `print!` for printing without appending a newline.
+trait Print {
+    /* Add things here */
+}
+impl<T: Print> SomethingOrNothing<T> {
+    fn print2(self) {
+        unimplemented!()
+    }
+}
+
+// **Exercise 03.2**: Building on exercise 02.2, implement all the things you need on `f32` to make your
+// program work with floating-point numbers.
+