How to create a method taking self or &self instead of creating two methods

help
1

A enum type Value has an assertion helper method must_be_int. Following is a tremble implementation for self and &self. How can I define one method instead of repeating myself expect using macro.

pub enum Value {
    Int(i32),
    String(String),
}

impl Value {
   pub fn must_be_int_take_ownership(self) -> i64 {
        match self {
            Int(i) => i,
            _ => panic!("It is not a int"),
        }
    }

   pub fn must_be_int_take_reference(&self) -> &i64 {
       match self {
            Int(i) => i,
            _ => panic!("It is not a int"),
        }
   }
2

Why would you need to take ownership at all?

3

some function take ownership of Value's associated value. If only defined a take reference method fn must_be_string(&self), then using clone() or to_owned() to transfer a reference type into a ownership one, it will cost a little.

fn consume_value(s: String) {...}

let v = Value::String("hello".to_string());
consume_value(v.must_be_string().clone())
4

What's your end goal?

  • Two distinct methods with the same name that return two distinct types
    • Probably you want a trait with method returning an associated type
  • Two distinct methods with the same name that can return one type which is a reference or owned
    • Probably you want a method returning a Cow
  • Two distinct methods with different names but not typing things twice
    • Probably you want the macro
  • Other
2 Likes
6

Examples of the first two bullets. (It's only on nightly for type_name_of_val to illustrate that it works as intended.)

7

Thanks for your examples. The trait with method returning an associated type work for me!!

8

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