ABI generation fails with Self return types

[miraclx]

#[near_bindgen]
impl MyType {
    pub fn new() -> Self { ... }
}

$ cargo build --features near-sdk/__abi-generate
   Compiling adder v0.1.0 (/Users/miraclx/git/near/near-sdk-rs/examples/adder)
error[E0411]: cannot find type `Self` in this scope
 --> src/lib.rs:3:12
  |
3 |     pub fn new() -> Self {
  |            ---      ^^^^ `Self` is only available in impls, traits, and type definitions
  |            |
  |            `Self` not allowed in a function

For more information about this error, try `rustc --explain E0411`.
error: could not compile `adder` due to 2 previous errors

[itegulov]

Is there a common use for Self outside of init functions though? Your particular example works if you mark the function with #[init].

[austinabell]

Is there a common use for Self outside of init functions though? Your particular example works if you mark the function with #[init].

Not a common one, but I think it is a valid one. I've seen devs try this, and it only doesn't really work when there are storage collections in the state. But if everything is in-memory and you just want to return all of the state, there could be a reason to do so.

new might be a confusing naming for the use case, though.

To confirm, this fails also, right?

#[near_bindgen]
// derive default, serde, ....
struct MyType {
  data: u8,
}

#[near_bindgen]
impl MyType {
  pub fn get_state(self) -> Self { self }
  // or
  pub fn get_state(&self) -> &Self { self }
}

[itegulov]

Not a common one, but I think it is a valid one. I've seen devs try this, and it only doesn't really work when there are storage collections in the state. But if everything is in-memory and you just want to return all of the state, there could be a reason to do so.

Makes sense.

I have taken a look at what ink! does with Self and they just ban its usage in non-constructor functions altogether:

So maybe banning all occurrences of Self makes more sense from the maintenance point of view.

[austinabell]

So maybe banning all occurrences of Self makes more sense from the maintenance point of view.

My intuition would agree with this. If they really wanted to serialize the state as a return value, they could use the type name explicitly or a number of other ways to work around.

Might be best to nudge devs away from this, as I've noticed a few times devs have accidentally forgotten to mark the fn as init