trait Deserialize<'de> {} trait DeserializeOwned: for<'de> Deserialize<'de> {} impl DeserializeOwned for T where T: for<'de> Deserialize<'de> {} // Based on this impl, `&'static str` only implements Deserialize<'static>. // It does not implement for<'de> Deserialize<'de>. impl<'de: 'a, 'a> Deserialize<'de> for &'a str {} fn main() { // Then why does it implement DeserializeOwned? This compiles. fn assert_deserialize_owned() {} assert_deserialize_owned::<&'static str>(); //~^ ERROR not general enough // It correctly does not implement for<'de> Deserialize<'de>. //fn assert_hrtb Deserialize<'de>>() {} //assert_hrtb::<&'static str>(); }