Summary
This may not be the best example, but for simplicity I am adapting the code from this issue. The problem is as follows:
The following return types work for new with the #[wasm_bindgen] attribute applied to the impl: Universe, Self, Option<Universe>. However, this return type appears not to work: Option<Self>. Is there some deep reason for this, or is this potentially a bug?
extern crate wasm_bindgen;
use wasm_bindgen::prelude::*;
#[repr(u8)]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Cell {
Dead = 0,
Alive = 1,
}
#[wasm_bindgen]
pub struct Universe {
width: u32,
height: u32,
cells: Vec<Cell>,
}
/// Public methods, exported to JavaScript.
#[wasm_bindgen]
impl Universe {
// The tutorial has the signature:
// pub fn new() -> Universe {
// This signature works:
// pub fn new() -> Option<Universe> {
pub fn new() -> Option<Self> {
let width = 128;
let height = 128;
let cells = (0..width * height)
.map(|i| {
if i % 2 == 0 || i % 7 == 0 {
Cell::Alive
} else {
Cell::Dead
}
})
.collect();
Some(Self {
width,
height,
cells,
})
}
}This gives the error:
error[E0401]: can't use generic parameters from outer function
--> src\lib.rs:177:28
|
139 | impl Universe {
| ---- `Self` type implicitly declared here, by this `impl`
...
177 | pub fn new() -> Option<Self> {
| ^^^^
| |
| use of generic parameter from outer function
| use a type here instead
The same problem arises when attempting to use Self with Result and other generics.
Summary
This may not be the best example, but for simplicity I am adapting the code from this issue. The problem is as follows:
The following return types work for
newwith the#[wasm_bindgen]attribute applied to the impl:Universe,Self,Option<Universe>. However, this return type appears not to work:Option<Self>. Is there some deep reason for this, or is this potentially a bug?This gives the error:
The same problem arises when attempting to use
SelfwithResultand other generics.