Rust requires an implementation to involve a local trait, a local type, or both. This prevents competing implementations for the same trait and type. section 2.2.3
Wrapping a nonlocal type
You cannot freely implement Clone for the nonlocal type String. Wrap String in a local newtype such as MyString, then implement Clone for MyString. Newtypes provide the workaround without runtime overhead, while macros can reduce the resulting boilerplate. section 2.2.3
Listing 2.7 The FirstName newtype
struct FirstName {
value: String,
}
impl FirstName {
pub fn new(name: &str) -> Result<FirstName, String> {
if name.len() < 2 {
Err("Name should be at least two characters".to_string())
} else {
Ok(FirstName {
value: name.to_string(),
})
}
}
pub fn get_value(&self) -> &String {
&self.value
}
}
// code for the other three newtypes
fn calculate_raise(first_name: FirstName, #1
_last_name: LastName,
_age: Age,
current_pay: Pay) -> Pay {
// ...
}
Inspect a Rust newtype that wraps String and exposes a controlled value accessor. section 2.2.3
