E0504: Question on non option

Explanation

The operand of ? is neither an exact specialization of the trusted std.option.Option producer nor an exact specialization of the trusted std.result.Result producer. Only those two standard-library types have Rue's built-in try behavior; an enum with the same variants is still a distinct, ordinary type.

Likely cause

The operand is a plain value, another type, or a user-defined Some/None or Ok/Err lookalike. Apply ? to a value produced by the standard Option or Result, or handle the operand's cases explicitly.

Examples

Apply try to a plain integer

fn main() -> i32 {
    let value = 42?;
    value
}

Apply try to a trusted Option

const option = @import("std/option.rue");
fn some_value() -> option.Option(i32) {
    let O = option.Option(i32);
    O.Some(42)
}
fn propagate() -> option.Option(i32) {
    let O = option.Option(i32);
    let value = some_value()?;
    O.Some(value)
}
fn main() -> i32 {
    propagate();
    0
}

References

• Trusted try operand producers