no_std 1.82 use anyhow

[zhang-wenchao]

use anyhow::Result;
use heapless::String;

pub fn test() -> Result<String<256>> {
    let mut phrase = String::new();
    phrase.push_str("XX")?;
    Ok(phrase)
}

   --> src/mnemonic.rs:310:26
    |
310 |     phrase.push_str("XX")?;
    |                          ^ the trait `core::error::Error` is not implemented for `()`, which is required by `Result<String<256>, anyhow::Error>: FromResidual<Result<Infallible, ()>>`
    |
    = help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
    = note: required for `anyhow::Error` to implement `From<()>`
    = note: required for `Result<String<256>, anyhow::Error>` to implement `FromResidual<Result<Infallible, ()>>`

I see the document say that it can be used directly by 1.81 or more? Is there any problem with my understanding?

[dtolnay]

What error message are you expecting test to return if the push_str fails?

[zhang-wenchao]

I actually do n’t pay attention to the wrong content. I can use it directly? Symbols are the best, I do so now.

pub fn test() -> Result<String<256>> {
    let mut phrase = String::new();
    phrase.push_str("XX").map_err(|_| anyhow!(""))?;
    Ok(phrase)
}

I use a translator, there may be errors in grammar. I hope you can understand and thank you very much.

[zhang-wenchao]

I notice that in the new version I can avoid using map_err. Am I understanding this incorrectly.

[zhang-wenchao]

It seems that core::error::Error cannot use the ? symbol directly.