Is there a way to simplify converting an Option into a Result without a macro?
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?
Solution 1:
The ok_or
and ok_or_else
methods convert Option
s to Result
s, 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)
}
Solution 2:
If you're using the crate anyhow
you can import the anyhow::Context
trait which adds the .context
method on Option
s to turn them into anyhow::Result
s:
use anyhow::{Result, Context};
fn new() -> Result<Boo> {
let item1 = section.get("item1").context("no item1")?;
let item2 = section.get("item2").context("no item2")?;
// whatever processing...
Ok(final_result)
}