Initial commit

solutions/23_conversions/from_into.rs

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+// The `From` trait is used for value-to-value conversions. If `From` is
+// implemented, an implementation of `Into` is automatically provided.
+// You can read more about it in the documentation:
+// https://doc.rust-lang.org/std/convert/trait.From.html
+
+#[derive(Debug)]
+struct Person {
+    name: String,
+    age: u8,
+}
+
+// We implement the Default trait to use it as a fallback when the provided
+// string is not convertible into a `Person` object.
+impl Default for Person {
+    fn default() -> Self {
+        Self {
+            name: String::from("John"),
+            age: 30,
+        }
+    }
+}
+
+impl From<&str> for Person {
+    fn from(s: &str) -> Self {
+        let mut split = s.split(',');
+        let (Some(name), Some(age), None) = (split.next(), split.next(), split.next()) else {
+            //                      ^^^^ there should be no third element
+            return Self::default();
+        };
+
+        if name.is_empty() {
+            return Self::default();
+        }
+
+        let Ok(age) = age.parse() else {
+            return Self::default();
+        };
+
+        Self {
+            name: name.into(),
+            age,
+        }
+    }
+}
+
+fn main() {
+    // Use the `from` function.
+    let p1 = Person::from("Mark,20");
+    println!("{p1:?}");
+
+    // Since `From` is implemented for Person, we are able to use `Into`.
+    let p2: Person = "Gerald,70".into();
+    println!("{p2:?}");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_default() {
+        let dp = Person::default();
+        assert_eq!(dp.name, "John");
+        assert_eq!(dp.age, 30);
+    }
+
+    #[test]
+    fn test_bad_convert() {
+        let p = Person::from("");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_good_convert() {
+        let p = Person::from("Mark,20");
+        assert_eq!(p.name, "Mark");
+        assert_eq!(p.age, 20);
+    }
+
+    #[test]
+    fn test_bad_age() {
+        let p = Person::from("Mark,twenty");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_missing_comma_and_age() {
+        let p: Person = Person::from("Mark");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_missing_age() {
+        let p: Person = Person::from("Mark,");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_missing_name() {
+        let p: Person = Person::from(",1");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_missing_name_and_age() {
+        let p: Person = Person::from(",");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_missing_name_and_invalid_age() {
+        let p: Person = Person::from(",one");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_trailing_comma() {
+        let p: Person = Person::from("Mike,32,");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+
+    #[test]
+    fn test_trailing_comma_and_some_string() {
+        let p: Person = Person::from("Mike,32,dog");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+}