finish ch10

ch10/traits/src/main.rs

@@ -3,6 +3,8 @@
 // behavior in an abstract way. Can use trait bounds to specify
 // that a generic type can be any type that has certain behavior
 
+use std::fmt::Display;
+
 // Like Haskell's deriving
 // Except orphans aren't allowed at all
 pub trait Summary {
@@ -89,6 +91,10 @@ fn main() {
     }
 
     // println!("The longest string is {result}");
+
+    // the static lifetime
+    // Can life for the duration of the program
+    let s: &'static str = "I have a static lifetime";
 }
 
 // fn notify<T: Summary>(item1: &T, item2: &T) {}
@@ -109,6 +115,7 @@ where
 // <'a> and 'a dispersed in the function parameters are
 // lifetime annotations. Lifetimes annotations are needed because
 // Rust can't tell whether the reference being returned refers to x or y
+// Feels like a similar vibe to Haskell `forall a`.
 fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
     if x.len() > y.len() {
         x
@@ -121,6 +128,44 @@ fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
 // with references passed as a parameter have lifetime annotations
 // passed implicitly due to soooooo many functions having this
 // lifetime annotation pattern used.
+//
+// Lifetimes on function/method parameters called input lifetimes.
+// Lifetimes on return values output lifetimes
+//
+// 3 Rules for lifetime functions
+// 1: Compiler assigns different lifetime parameter to each lifetime
+//    in each input type
+//    fn foo(x: &i32) becomes fn foo<'a>(x: &'a i32)
+//    fn foo(x: &i32, y: &i32) becomes fn foo<'a, 'b>(x: &'a i32, y: &'b i32)
+//    fn foo(x: &ImportantExcerpt) becomes fn foo<'a, 'b>(x: &'a ImportantExcerpt<'b>)
+// 2: If exactly one input lifetime paramter, lifetime applied to all output
+//    lifetime parameters
+// 3: If multiple input lifetime parameters, but one of them is &self or &mut self,
+//    lifetime of self assigned to all output lifetime parameters
 
-// Stopped here pre red river gorge:
-// https://rust-book.cs.brown.edu/ch10-03-lifetime-syntax.html#lifetime-elision
+// Lifetime annotations in method definitions
+
+impl<'a> ImportantExcerpt<'a> {
+    fn level(&self) -> i32 {
+        3
+    }
+
+    // example of third lifetime elision rule
+    fn announce_and_return_part(&self, announcement: &str) -> &str {
+        println!("Attention Please: {announcement}");
+        self.part
+    }
+}
+
+// Generic Type Paramters, trait bounds, and lifetimes together
+fn longest_with_an_announcement<'a, T>(x: &'a str, y: &'a str, ann: T) -> &'a str
+where
+    T: Display,
+{
+    println!("Announcement!: {ann}");
+    if x.len() > y.len() {
+        x
+    } else {
+        y
+    }
+}