coding 12、13

exercises/12_options/options1.rs

@@ -3,7 +3,9 @@
 // someone eats it all, so no icecream is left (value 0). Return `None` if
 // `hour_of_day` is higher than 23.
 fn maybe_icecream(hour_of_day: u16) -> Option<u16> {
-    // TODO: Complete the function body.
+    if hour_of_day < 22 { Some(5) }
+    else if hour_of_day < 24 { Some(0) }
+    else { None }
 }
 
 fn main() {
@@ -18,7 +20,7 @@ mod tests {
     fn raw_value() {
         // TODO: Fix this test. How do you get the value contained in the
         // Option?
-        let icecreams = maybe_icecream(12);
+        let icecreams = maybe_icecream(12).unwrap();
 
         assert_eq!(icecreams, 5); // Don't change this line.
     }

exercises/12_options/options2.rs

@@ -10,7 +10,7 @@ mod tests {
         let optional_target = Some(target);
 
         // TODO: Make this an if-let statement whose value is `Some`.
-        word = optional_target {
+        if let Some(word) = optional_target {
             assert_eq!(word, target);
         }
     }
@@ -29,7 +29,7 @@ mod tests {
         // TODO: Make this a while-let statement. Remember that `Vec::pop()`
         // adds another layer of `Option`. You can do nested pattern matching
         // in if-let and while-let statements.
-        integer = optional_integers.pop() {
+        while let Some(Some(integer)) = optional_integers.pop() {
             assert_eq!(integer, cursor);
             cursor -= 1;
         }

exercises/12_options/options3.rs

@@ -9,7 +9,7 @@ fn main() {
 
     // TODO: Fix the compiler error by adding something to this match statement.
     match optional_point {
-        Some(p) => println!("Co-ordinates are {},{}", p.x, p.y),
+        Some(ref p) => println!("Co-ordinates are {},{}", p.x, p.y),
         _ => panic!("No match!"),
     }
 

exercises/13_error_handling/errors1.rs

@@ -4,12 +4,12 @@
 // construct to `Option` that can be used to express error conditions. Change
 // the function signature and body to return `Result<String, String>` instead
 // of `Option<String>`.
-fn generate_nametag_text(name: String) -> Option<String> {
+fn generate_nametag_text(name: String) -> Result<String, String> {
     if name.is_empty() {
         // Empty names aren't allowed.
-        None
+        Err("Empty names aren't allowed".to_string())
     } else {
-        Some(format!("Hi! My name is {name}"))
+        Ok(format!("Hi! My name is {name}"))
     }
 }
 

exercises/13_error_handling/errors2.rs

@@ -22,8 +22,10 @@ fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
 
     // TODO: Handle the error case as described above.
     let qty = item_quantity.parse::<i32>();
-
-    Ok(qty * cost_per_item + processing_fee)
+    match qty {
+        Ok(v) => { Ok(v * cost_per_item + processing_fee) }
+        Err(e) => { Err(e) }
+    }
 }
 
 fn main() {

exercises/13_error_handling/errors3.rs

@@ -19,7 +19,7 @@ fn main() {
     let mut tokens = 100;
     let pretend_user_input = "8";
 
-    let cost = total_cost(pretend_user_input)?;
+    let cost = total_cost(pretend_user_input).unwrap();
 
     if cost > tokens {
         println!("You can't afford that many!");

exercises/13_error_handling/errors4.rs

@@ -11,8 +11,13 @@ struct PositiveNonzeroInteger(u64);
 
 impl PositiveNonzeroInteger {
     fn new(value: i64) -> Result<Self, CreationError> {
-        // TODO: This function shouldn't always return an `Ok`.
-        Ok(Self(value as u64))
+        if value > 0 {
+            Ok(Self(value as u64))
+        } else if value == 0 {
+            Err(CreationError::Zero)
+        } else {
+            Err(CreationError::Negative)
+        }
     }
 }
 

exercises/13_error_handling/errors5.rs

@@ -48,7 +48,7 @@ impl PositiveNonzeroInteger {
 
 // TODO: Add the correct return type `Result<(), Box<dyn ???>>`. What can we
 // use to describe both errors? Is there a trait which both errors implement?
-fn main() {
+fn main() -> Result<(), Box<dyn Error>> {
     let pretend_user_input = "42";
     let x: i64 = pretend_user_input.parse()?;
     println!("output={:?}", PositiveNonzeroInteger::new(x)?);

exercises/13_error_handling/errors6.rs

@@ -25,7 +25,7 @@ impl ParsePosNonzeroError {
     }
 
     // TODO: Add another error conversion function here.
-    // fn from_parseint(???) -> Self { ??? }
+    fn from_parseint(err: ParseIntError) -> Self { Self::ParseInt(err) }
 }
 
 #[derive(PartialEq, Debug)]
@@ -43,7 +43,7 @@ impl PositiveNonzeroInteger {
     fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
         // TODO: change this to return an appropriate error instead of panicking
         // when `parse()` returns an error.
-        let x: i64 = s.parse().unwrap();
+        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
         Self::new(x).map_err(ParsePosNonzeroError::from_creation)
     }
 }