Is there a way to simplify converting an Option into a Result without a macro?

问题

I have something like this (the real function is Ini::Section::get from rust-ini):

impl Foo {
    pub fn get<K>(&'a mut self, key: &K) -> Option<&'a str>
    where
        K: Hash + Eq,
    {
        // ...
    }
}

I have to call it several times:

fn new() -> Result<Boo, String> {
    let item1 = match section.get("item1") {
        None => return Result::Err("no item1".to_string()),
        Some(v) => v,
    };
    let item2 = match section.get("item2") {
        None => return Result::Err("no item2".to_string()),
        Some(v) => v,
    };
}

To remove code bloat, I can write a macro like this:

macro_rules! try_ini_get {
    ($e:expr) => {
        match $e {
            Some(s) => s,
            None => return Result::Err("no ini item".to_string()),
        }
    }
}

Is there any way to remove the code duplication without this macro implementation?

回答1:

The ok_or and ok_or_else methods convert Options to Results, and the ? operator automates the boilerplate associated with early Err returns.

You could do something like:

fn new() -> Result<Boo, String> {
    let item1 = section.get("item1").ok_or("no item1")?;
    let item2 = section.get("item2").ok_or("no item2")?;
    // whatever processing...
    Ok(final_result)
}

来源：https://stackoverflow.com/questions/37890405/is-there-a-way-to-simplify-converting-an-option-into-a-result-without-a-macro