added day 16

Author: jsoverson

Cargo.lock

@@ -85,3 +85,29 @@ These examples require setting an environment variable. How to do that in your e
 - `MARKDOWN=README.md cargo run -p day-14-thiserror`
 - `MARKDOWN=README.md cargo run -p day-14-error-chain`
 - `MARKDOWN=README.md cargo run -p day-14-snafu`
+
+### Day 16
+
+#### Closures
+
+- `cargo run -p day-15-closures`
+
+### Day 16
+
+#### Type differences
+
+- `cargo run -p day-16-type-differences --bin impl-owned`
+- `cargo run -p day-16-type-differences --bin impl-borrowed`
+
+#### `'static`
+
+- `cargo run -p day-16-static` - intentionally does not compile
+- `cargo run -p day-16-static-bounds` - intentionally does not compile
+
+#### Lifetime elision
+
+- `cargo run -p day-16-elision`
+
+#### Unsafe pointers
+
+- `cargo run -p day-16-unsafe-pointers`

README.md

@@ -0,0 +1,8 @@
+[package]
+name = "day-16-elision"
+version = "0.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

crates/day-16/elision/Cargo.toml

@@ -0,0 +1,15 @@
+fn omits_annotations(list: &[String]) -> Option<&String> {
+  list.get(0)
+}
+
+fn has_annotations<'a>(list: &'a [String]) -> Option<&'a String> {
+  list.get(1)
+}
+
+fn main() {
+  let authors = vec!["Samuel Clemens".to_owned(), "Jane Austen".to_owned()];
+  let value = omits_annotations(&authors).unwrap();
+  println!("The first author is '{}'", value);
+  let value = has_annotations(&authors).unwrap();
+  println!("The second author is '{}'", value);
+}

crates/day-16/elision/src/main.rs

@@ -0,0 +1,8 @@
+[package]
+name = "day-16-static-bounds"
+version = "0.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

crates/day-16/static-bounds/Cargo.toml

@@ -0,0 +1,45 @@
+use std::fmt::Display;
+
+fn main() {
+  let mut string = "First".to_owned();
+
+  string.push_str(string.to_uppercase().as_str());
+  print_a(&string);
+  print_b(&string);
+  print_c(&string); // Compilation error
+  print_d(&string); // Compilation error
+  print_e(&string);
+  print_f(&string);
+  print_g(&string); // Compilation error
+}
+
+fn print_a<T: Display + 'static>(t: &T) {
+  println!("{}", t);
+}
+
+fn print_b<T>(t: &T)
+where
+  T: Display + 'static,
+{
+  println!("{}", t);
+}
+
+fn print_c(t: &'static dyn Display) {
+  println!("{}", t)
+}
+
+fn print_d(t: &'static impl Display) {
+  println!("{}", t)
+}
+
+fn print_e(t: &(dyn Display + 'static)) {
+  println!("{}", t)
+}
+
+fn print_f(t: &(impl Display + 'static)) {
+  println!("{}", t)
+}
+
+fn print_g(t: &'static String) {
+  println!("{}", t);
+}

crates/day-16/static-bounds/src/main.rs

@@ -0,0 +1,8 @@
+[package]
+name = "day-16-static"
+version = "0.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

crates/day-16/static/Cargo.toml

@@ -0,0 +1,28 @@
+use std::fmt::Display;
+
+fn main() {
+  let r1;
+  let r2;
+  {
+    static STATIC_EXAMPLE: i32 = 42;
+    r1 = &STATIC_EXAMPLE;
+    let x = "&'static str";
+    r2 = x;
+  }
+  println!("&'static i32: {}", r1);
+  println!("&'static str: {}", r2);
+
+  let r3;
+
+  {
+    let string = "String".to_owned();
+
+    static_bound(&string); // This is *not* an error
+    r3 = &string; // This *is*
+  }
+  println!("{}", r3);
+}
+
+fn static_bound<T: Display + 'static>(t: &T) {
+  println!("{}", t);
+}

crates/day-16/static/src/main.rs

@@ -0,0 +1,20 @@
+[package]
+name = "day-16-type-differences"
+version = "0.0.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[[bin]]
+name = "impl-owned"
+test = false
+bench = false
+path = "src/impl-owned.rs"
+
+[[bin]]
+name = "impl-borrowed"
+test = false
+bench = false
+path = "src/impl-borrowed.rs"

crates/day-16/type-differences/Cargo.toml

@@ -0,0 +1,46 @@
+use std::fmt::Display;
+
+fn main() {
+  let my_struct = MyStruct {};
+  // my_struct.print();  // Removed because the impl no longer exists
+  println!("<intentionally removed this Foo>");
+
+  let struct_ref = &my_struct;
+  struct_ref.print();
+
+  let mut mut_struct = MyStruct {};
+  // mut_struct.print();  // Removed because the impl no longer exists
+  println!("<intentionally removed this Foo>");
+
+  let ref_mut_struct = &mut_struct;
+  ref_mut_struct.print();
+
+  let mut_struct_ref = &mut mut_struct;
+  mut_struct_ref.print();
+}
+
+trait Printer {
+  fn print(&self);
+}
+
+struct MyStruct {}
+
+// Watch how the output differs when this impl is removed.
+//
+// impl Printer for MyStruct {
+//   fn print(&self) {
+//     println!("Foo")
+//   }
+// }
+
+impl Printer for &MyStruct {
+  fn print(&self) {
+    println!("&Foo")
+  }
+}
+
+impl Printer for &mut MyStruct {
+  fn print(&self) {
+    println!("&mut Foo")
+  }
+}