How can I pattern match against an Option?

It’s a known limitation of Rust’s patterns.

Method calls (including internal methods for operators like ==) automatically call .deref() as needed, so String gets automagically turned into &str for comparisons with literals.

On the other hand, the patterns are quite literal in their comparisons, and find that String and &str are different.

There are two solutions:

1. Change Option<String> to Option<&str> before matching on it: Some(a).as_deref(). The as_deref() is a combo of as_ref() that makes Option<&String> (preventing move), and deref()/as_str() then unambiguously references it as a &str.

2. Use match guard: match Some(a) { Some(ref s) if s == "hello" => … }. Some(ref s) matches any String, and captures it as s: &String, which you can then compare in the if guard which does the usual flexible coercions to make it work.

See also:

• Converting from Option<String> to Option<&str>