unfmt
is a compile-time pattern matching library that reverses the
interpolation process of format!
.
You can think of it as an extremely lightweight regular expression engine without the runtime pattern-compilation cost.
cargo add -D unfmt
let value = "My name is Rho.";
// Unnamed captures are returned as tuples.
assert_eq!(
unformat!("My {} is {}.", value),
Some(("name", "Rho"))
);
// You can put indices as well; just make sure ALL captures use indices
// otherwise it's not well defined.
assert_eq!(
unformat!("My {1} is {0}.", value),
Some(("Rho", "name"))
);
// You can also name captures using variables, but make sure you check the
// return is not None.
let subject;
let object;
assert_eq!(
unformat!("My {subject} is {object}.", value),
Some(())
);
assert_eq!((subject, object), (Some("name"), Some("Rho")));
// If a type implements `FromStr`, you can use it as a type argument. This
// is written as `{:Type}`.
assert_eq!(
unformat!("Listening on {:url::Url}", "Listening on http://localhost:3000"),
Some((url::Url::from_str("http://localhost:3000").unwrap(),))
);
In general, captures are written as {<index-or-variable>:<type>}
. Multiple
captures in a row (i.e. {}{}
) are not supported as they aren't well-defined.
- There is no backtracking.