moved arrays to it's own file

src/arrays.rs

@@ -0,0 +1,67 @@
+#[derive(Debug, PartialEq)]
+pub struct EmptyListError;
+
+// implementing Error for my error to satisfy Box<dyn std::error::Error>
+// not needed ATM
+// impl std::error::Error for EmptyListError {}
+
+// so we can pass EmptyListError to println!
+impl std::fmt::Display for EmptyListError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Error: list must not be empty")
+    }
+}
+
+// Result<...,Box<dyn std::error::Error>> is overkill
+// this is intuitive enough for caller error detection 
+// actually probably should use Option instead, but this is better for extension
+pub fn min_and_max(list: &[u32]) -> Result<(u32, u32), EmptyListError> {
+    if list.is_empty() {
+        return Err(EmptyListError);
+    }
+    let mut min:u32 = 100;
+    let mut max:u32 = 0;
+    for i in list {
+        if *i > max {
+            max = *i;
+        } 
+        if *i < min {
+            min = *i;
+        }
+    } 
+    Ok((min,max))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*; // need access to functions above
+
+    #[test]
+    fn test_arrays() {
+        // empty array
+        let empty = [];
+        let empty_min_and_max = min_and_max(&empty);
+        assert!(empty_min_and_max.as_ref().is_err()); // as_ref() so we don't perform move
+        assert!(*(empty_min_and_max.as_ref().err().unwrap()) == EmptyListError);
+        println!("Expected: {}", *(empty_min_and_max.as_ref().err().unwrap()));
+
+        // array - contiguous, entirely on the stack, fixed at compile time, no pointer indirection
+        let l = [ 1, 2, 10, 100, 50, 75, 36, 21];
+        let l_min_and_max = min_and_max(&l);
+        assert!(l_min_and_max.as_ref().unwrap().0 == 1);
+        assert!(l_min_and_max.as_ref().unwrap().1 == 100);
+
+        // vec - stack: ptr, len, cap; ptr -> heap: contiguous allocation of capacity
+        // when variable goes out of scope drop() is called to deallocate the heap
+        let v = vec![1,2,3];
+        let v_min_and_max = min_and_max(&v);
+        assert!(v_min_and_max.as_ref().unwrap().0 == 1);
+        assert!(v_min_and_max.as_ref().unwrap().1 == 3);
+
+        let s = String::from("hello");
+        let r = &s;
+        println!("{}", *r); // works because there is no implicit move
+        // let thing = *r; // doesn't work because String does not implement Copy trait
+
+    }
+}

src/main.rs

@@ -1,4 +1,5 @@
 mod string;
+mod arrays;
 mod fmt_debug;
 
 // when a String is passed to this function a move occurs:
@@ -112,14 +113,5 @@ fn main() {
 
     // todo: Cow
     println!("Learning Rust");
-
-    let empty = [];
-    let empty_min_and_max = min_and_max(&empty);
-    assert!(empty_min_and_max.as_ref().is_err());
-    assert!(*(empty_min_and_max.as_ref().err().unwrap()) == EmptyListError);
-
-    let l = [ 1, 2, 10, 100, 50, 75, 36, 21];
-    let l_min_and_max = min_and_max(&l);
-    assert!(l_min_and_max.as_ref().unwrap().0 == 1);
-    assert!(l_min_and_max.as_ref().unwrap().1 == 100);
 }
+