Pre-RFC: Catching Functions

language design
255

If we introduce Ok wrapping in try blocks it’s reasonable to make this wrapping mandatory and to cover only one level of wrapping, i.e. this code will result in a compilation errors:

try fn foo() -> Result<u32, E> {
    Ok(1u32)
}

try fn foo2() -> Result<u32, E> {
    Err(e)
}

try fn bar() -> Option<Option<u32>> {
    1u32
}

At first it could look a bit strange, but without this strict rule it will be much harder to reason about code behaviour. Thus you example will look like this:

try fn foo() -> Result<Result<u32, E1>, E2> {
    // returns Err(e1)
    if a { throw e1; }
    // returns Ok(Err(e2))
    if b { return Err(e2); }
    // returns Ok(Ok(1u32))
    Ok(1u32)
    // writing simply `1u32` will result in a compilation error
    // same goes for `return Ok(Ok(1u32))` and `return Ok(Err(e2))`
}
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