Function enum_err 

pub fn enum_err<'a, T, E>() -> EnumKp<Result<T, E>, E, &'a Result<T, E>, &'a E, &'a mut Result<T, E>, &'a mut E, for<'b> fn(&'b Result<T, E>) -> Option<&'b E>, for<'b> fn(&'b mut Result<T, E>) -> Option<&'b mut E>, fn(E) -> Result<T, E>>

Extract from Result<T, E> - Err variant

Example

use rust_key_paths::enum_err;
let result: Result<String, i32> = Err(42);
let err_kp = enum_err();
assert_eq!(err_kp.get(&result), Some(&42));