Complete errors exercises

exercises/error_handling/errors1.rs

@@ -5,14 +5,12 @@
 // construct to `Option` that can be used to express error conditions. Let's use it!
 // Execute `rustlings hint errors1` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
-pub fn generate_nametag_text(name: String) -> Option<String> {
+pub fn generate_nametag_text(name: String) -> Result<String, String> {
     if name.is_empty() {
         // Empty names aren't allowed.
-        None
+        Err("`name` was empty; it must be nonempty.".into())
     } else {
-        Some(format!("Hi! My name is {}", name))
+        Ok(format!("Hi! My name is {}", name))
     }
 }
 

exercises/error_handling/errors2.rs

@@ -17,15 +17,12 @@
 // one is a lot shorter!
 // Execute `rustlings hint errors2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
     let processing_fee = 1;
     let cost_per_item = 5;
-    let qty = item_quantity.parse::<i32>();
-
+    let qty = item_quantity.parse::<i32>()?;
     Ok(qty * cost_per_item + processing_fee)
 }
 

exercises/error_handling/errors3.rs

@@ -4,11 +4,9 @@
 // Why not? What should we do to fix it?
 // Execute `rustlings hint errors3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
-fn main() {
+fn main() -> Result<(), ParseIntError> {
     let mut tokens = 100;
     let pretend_user_input = "8";
 
@@ -16,9 +14,11 @@ fn main() {
 
     if cost > tokens {
         println!("You can't afford that many!");
+        Ok(())
     } else {
         tokens -= cost;
         println!("You now have {} tokens.", tokens);
+        Ok(())
     }
 }
 

exercises/error_handling/errors4.rs

@@ -1,8 +1,6 @@
 // errors4.rs
 // Execute `rustlings hint errors4` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 #[derive(PartialEq, Debug)]
 struct PositiveNonzeroInteger(u64);
 
@@ -14,8 +12,13 @@ enum CreationError {
 
 impl PositiveNonzeroInteger {
     fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
-        // Hmm...? Why is this only returning an Ok value?
-        Ok(PositiveNonzeroInteger(value as u64))
+        if value > 0 {
+            Ok(PositiveNonzeroInteger(value as u64))
+        } else if value < 0 {
+            Err(CreationError::Negative)
+        } else {
+            Err(CreationError::Zero)
+        }
     }
 }
 

exercises/error_handling/errors5.rs

@@ -16,14 +16,11 @@
 
 // Execute `rustlings hint errors5` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
+use std::error::Error;
+use std::fmt::Result as FmtResult;
+use std::fmt::{Display, Formatter};
 
-use std::error;
-use std::fmt;
-use std::num::ParseIntError;
-
-// TODO: update the return type of `main()` to make this compile.
-fn main() -> Result<(), Box<dyn ???>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let pretend_user_input = "42";
     let x: i64 = pretend_user_input.parse()?;
     println!("output={:?}", PositiveNonzeroInteger::new(x)?);
@@ -52,8 +49,8 @@ impl PositiveNonzeroInteger {
 }
 
 // This is required so that `CreationError` can implement `error::Error`.
-impl fmt::Display for CreationError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+impl Display for CreationError {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
         let description = match *self {
             CreationError::Negative => "number is negative",
             CreationError::Zero => "number is zero",
@@ -62,4 +59,4 @@ impl fmt::Display for CreationError {
     }
 }
 
-impl error::Error for CreationError {}
+impl Error for CreationError {}

exercises/error_handling/errors6.rs

@@ -8,8 +8,6 @@
 
 // Execute `rustlings hint errors6` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
 // This is a custom error type that we will be using in `parse_pos_nonzero()`.
@@ -23,15 +21,17 @@ impl ParsePosNonzeroError {
     fn from_creation(err: CreationError) -> ParsePosNonzeroError {
         ParsePosNonzeroError::Creation(err)
     }
-    // TODO: add another error conversion function here.
-    // fn from_parseint...
+
+    fn from_parseint(err: ParseIntError) -> ParsePosNonzeroError {
+        ParsePosNonzeroError::ParseInt(err)
+    }
 }
 
 fn parse_pos_nonzero(s: &str) -> Result<PositiveNonzeroInteger, ParsePosNonzeroError> {
-    // TODO: change this to return an appropriate error instead of panicking
-    // when `parse()` returns an error.
-    let x: i64 = s.parse().unwrap();
-    PositiveNonzeroInteger::new(x).map_err(ParsePosNonzeroError::from_creation)
+    match s.parse() {
+        Ok(v) => PositiveNonzeroInteger::new(v).map_err(ParsePosNonzeroError::from_creation),
+        Err(parse_int_error) => Err(ParsePosNonzeroError::from_parseint(parse_int_error)),
+    }
 }
 
 // Don't change anything below this line.