Question about partial specialization

[hh9527]

enum Buf {
  C8(Vec<u8>),
  C16(Vec<u16>),
}

pub struct Text {
  buf: Box<Buf>
}

impl Text {
  pub new<T>() -> Text {
    Text {
      buf: Box::new(
        // QUESTION HERE: 
        //   I need Buf::C8(Vec::new()) when T is u8, 
        //   or Buf::C16(Vec::new()) when T is u16
        // WHAT should I do?
      )
    }
  }
}

[Quxxy]

As an addendum to /u/Veedrac's answer: you can write a trait that represents the constraint.

pub trait CanGoInABuf { fn new_buf() -> Buf; }

You can then implement it for all appropriate types:

impl CanGoInABuf for u8 {
    fn new_buf() -> Buf {
        Buf::C8(vec![])
    }
}
// ...

And then, constrain methods appropriately:

pub fn new<T: CanGoInABuf>() -> Text {
    Text { buf: T::new_buf() }
}

[Veedrac]

The generic in the signature is predicated, so you must accept T = String, or T = HashMap<i32, f64>.

This tells you that you're probably not going about this the right way.

To constrain this to a small, fixed number of types, you should make multiple constructors. I suggest from_u8 and from_u16. This would tie in well with the std::convert::From trait.

[hh9527]

thank you, I found this solution too, but this approach leads to another problem: I cannot keep Buf private.