more progress

REVISITS.md

@@ -16,4 +16,6 @@ return results to new Vec<i32> vector
 15) options1 (understand Some and None)
 16) option2 (important to understand if let, while let statements alternative to match ). ChatGPT explanation was great.
 17) errors2 make sure you understand error propagation but also the long-form solution (just for understanding). "The ? placed after a Result value is defined to work in almost the same way as the match expressions we defined to handle the Result values in Listing 9-6. If the value of the Result is an Ok, the value inside the Ok will get returned from this expression, and the program will continue. If the value is an Err, the Err will be returned from the whole function as if we had used the return keyword so the error value gets propagated to the calling code."
+18) errors3
+19) HAVE to revisit error5 - > great pre-intro to Box<dyn `Trait`>
 

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);
 
@@ -15,7 +13,14 @@ 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::Zero)
+        } else {
+            Err(CreationError::Negative)
+        }
+        
     }
 }
 

exercises/error_handling/errors5.rs

@@ -16,14 +16,12 @@
 
 // Execute `rustlings hint errors5` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 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::Error>> {
     let pretend_user_input = "42";
     let x: i64 = pretend_user_input.parse()?;
     println!("output={:?}", PositiveNonzeroInteger::new(x)?);