Impl trait for struct with lifetime parameter

help
#1 
pub trait Key {
    fn from_u8(key: &[u8]) -> Self;
    fn as_slice<T, F: Fn(&[u8]) -> T>(&self, f: F) -> T;
}

pub fn from_u8<K: Key>(key: &[u8]) -> K {
    Key::from_u8(key)
}

struct MyKey<'a>(&'a [u8]);

impl Key for MyKey<'_> {
    fn from_u8(key: &[u8]) -> Self {
        MyKey(key)
    }

    fn as_slice<T, F: Fn(&[u8]) -> T>(&self, f: F) -> T {
        f(&self.0)
    }
}

How can I impl from_u8 for MyStruct, the compiler tells that "cannot infer an appropriate lifetime for lifetime parameter 'a due to conflicting requirements".

#2

You can make the trait generic on the lifetime.

#3

If the trait is from outter crate, it can't be changed, is there any way to pass the compiling?

#4

Only if you do something like owning the data instead. The trait function signature as-is says "I can make Self out of a slice with an arbitrary lifetime".

1 Like
#5

If the trait declares that from_u8()'s key parameter has a lifetime shorter than your Key type it means you'll need to make your own copy of the key.

#6

Get it, thanks very much.