A custom error type in Rust
Rust interview exercise on Option & Result, difficulty 3 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write get_port(config) that reads the "port" key and parses it as a u16. A missing key is ConfigError::Missing("port"); a value that does not parse is ConfigError::Invalid with the key and the raw value. Also implement Display: "missing key: port" and "invalid value for port: abc".
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