Generic functions in Rust

Question

I would like create shared library (plugin) with generic function. T can be : u8, u16, u32, float, i8, i16, i32.

pub struct Api {}
    impl Api {
        pub fn write_to_slave<T>(&self, id: u32, value: T)
        {
            println!("write to slave id : {}, value: {}", id, value);
        }
    }

Error:

   |
18 |     pub fn write_to_slave<T>(&self, id: u32, value: T)
   |                           - help: consider restricting this bound: `T: std::fmt::Display`
19 |     {
20 |         println!("write to slave id : {}, value: {}", id, value);
   |                                                           ^^^^^ `T` cannot be formatted with the default formatter
   |
   = help: the trait std::fmt::Display is not implemented for T
   = note: in format strings you may be able to use {:?} (or {:#?} for pretty-print) instead
   = note: required by std::fmt::Display::fmt```

Have you tried what the error message suggests to do? It helpfully shows you the exact trait bound you need to include to make this code compile. — Sven Marnach
– Sven Marnach, Commented Feb 7, 2020 at 16:14

Chris · Accepted Answer · 2020-02-07 21:19:01Z

5

As the commenter mentioned. You need to specify a trait bound on your generic type T, see below. This requires that the type T implements the Display trait. Here is a link to the Rust docs for this topic.

pub struct Api {}
impl Api {
   pub fn write_to_slave<T: Display>(&self, id: u32, value: T)
      {
         println!("write to slave id : {}, value: {}", id, value);
      }
}

answered Feb 7, 2020 at 21:19

Chris

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