E0505: Question outside result fn

Explanation

The operand of ? is a trusted standard-library Result, but the enclosing function does not return a trusted standard-library Result. On Err(e), ? immediately returns an Err(e) constructed with the enclosing function's Result type, so that return type must be std.result.Result(U, E).

Likely cause

A Result-producing call was followed by ? inside a function returning a plain value, Option, or a user-defined Result-shaped enum. Change the function to return the standard Result, handle Ok and Err explicitly with match, or remove ?.

Examples

Propagate Result from a plain-value function

const result = @import("std/result.rue");
fn fallible() -> result.Result(i32, i32) {
    let R = result.Result(i32, i32);
    R.Ok(42)
}
fn main() -> i32 {
    fallible()?
}

Return trusted Result before propagating

const result = @import("std/result.rue");
fn fallible() -> result.Result(i32, i32) {
    let R = result.Result(i32, i32);
    R.Ok(42)
}
fn run() -> result.Result(i32, i32) {
    let R = result.Result(i32, i32);
    let value = fallible()?;
    R.Ok(value)
}
fn main() -> i32 {
    run();
    0
}

References

• Try operand and enclosing producer compatibility