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pub trait Tag: 'static + Hash + Eq + FromStr + Display + Debug + Clone + Send + Sync { }

Represents a “string-able” type.

The type is required to be able to be represented as a string Display, along with knowing how to be parsed from the string representation FromStr. To make sure things stay easy to debug, both the Tag and the FromStr::Err must implement Debug.

Clone, Hash, and Eq are needed so that it can represent un-hashable types.

Send and Sync and 'static are current requirements due to how it is sometimes sent across thread boundaries, although some of those constraints may relax in the future.

The simplest type that fits all these requirements is a String.

Handling Errors#

Because we leave it up to the type to implement FromStr, if an error is returned during parsing then Tauri will std::panic! with the string it failed to parse.

To avoid Tauri panicking during the application runtime, have your type be able to handle unknown events and never return an error in FromStr. Then it will be up to your own code to handle the unknown event.


use std::fmt;
use std::str::FromStr;

#[derive(Debug, Clone, Hash, Eq, PartialEq)]
enum Event {

impl fmt::Display for Event {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    f.write_str(match self {
      Self::Foo => "foo",
      Self::Bar => "bar",
      Self::Unknown(s) => &s

impl FromStr for Event {
  type Err = std::convert::Infallible;

  fn from_str(s: &str) -> Result<Self, Self::Err> {
    Ok(match s {
      "foo" => Self::Foo,
      "bar" => Self::Bar,
      other => Self::Unknown(other.to_string())

// safe to unwrap because we know it's infallible due to our FromStr implementation.
let event: Event = "tauri://file-drop".parse().unwrap();

// show that this event type can be represented as a Tag, a requirement for using it in Tauri.
fn is_file_drop(tag: impl tauri_runtime::tag::Tag) {
  assert_eq!("tauri://file-drop", tag.to_string());



impl<T, E> Tag for T where T: Hash + Eq + FromStr<Err = E> + Display + Debug + Clone + Send + Sync + 'static, E: Debug,#

Automatically implement Tag for all types that fit the requirements.

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