The From trait defines how one type becomes another. Choose a source type and a destination type, then provide the conversion in an implementation. Rust’s standard library uses From widely, including conversions from &str and String into Vec<u8>. section 7.2
A From implementation connects two types with a familiar constructor-like call:
- Vec::from([8, 9, 10]) creates a vector containing the array’s numbers. section 7.2
- Vec::from("hello") and Vec::from(String::from("hello")) produce Vec<u8> values containing the string’s bytes. section 7.2
- Implementing From<Vec<City>> for Country allows Country::from(vector_of_cities) to collect cities into a country. section 7.2
Converting cities into a country
Define Country with a Vec<City>, then implement From<Vec<City>> for Country. The implementation receives the cities and returns Country { cities }. Code can then create Helsinki and Turku, place them in a vector, and convert that vector into a Country before printing each city and its population. section 7.2
From<&'_ [T]> From<&'_ mut [T]> From<&'_ str> From<&'a Vec<T>> From<[T; N]> From<BinaryHeap<T>> From<String>> From<Vec<T>> From<VecDeque<T>>
Browse representative standard-library From implementations, including slices, strings, arrays, vectors, and collection types. section 7.2
