Add code

example_5/.gitignore

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+/target

example_5/Cargo.toml

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+[package]
+name = "example_5"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

example_5/src/main.rs

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+struct Years(i64);
+struct Days(i64);
+
+impl Years {
+    pub fn to_days(&self) -> Days {
+        Days(self.0 * 365)
+    }
+}
+
+impl Days {
+    /// truncates partial years
+    pub fn to_years(&self) -> Years {
+        Years(self.0 / 365)
+    }
+}
+
+fn is_adult(age: &Years) -> bool {
+    age.0 >= 18
+}
+
+fn main() {
+    let age = Years(25);
+    let age_days = age.to_days();
+    println!("Is an adult? {}", is_adult(&age));
+    println!("Is an adult? {}", is_adult(&age_days.to_years()));
+    // println!("Is an adult? {}", is_adult(&age_days));
+}