thread_scoped_ref

A library that is similar to a thread local storage but allows to store references / dyn Trait within a scope. It can be used to 'inject' references (if you don't own the data) into functions you don't control (e.g. functions from an external library).

Cargo

[dependencies]

thread-scoped-ref = "0"

More information

See crates.io, the documentation and the tests.

Example

use thread_scoped_ref::{thread_scoped_ref, scoped, with};

/// Declare the `REF_TO_A_STRING`.
thread_scoped_ref!(REF_TO_A_STRING, str);

/// This function reads the value and prints the value. This function is usually called by an external
/// library you don't control.
fn value_consumer() {
  with(&REF_TO_A_STRING, |maybe_string| {
    // `maybe_string` is `Some` if this is called within a scope, or `None` if not called
    // within a scope.
    if let Some(string) = maybe_string {
      println!("String is: '{}'", string);
    } else {
      println!("There's no string.");
    }
  });
}

// Example #1: prints `There's no string` (since not called within a scope).
value_consumer();

// Example #2: With a scope.
let my_string = "The String!".to_string();
// note: We use the reference and not the actual string. It's not static!
let my_string_ref = &my_string;
scoped(&REF_TO_A_STRING, my_string_ref, || {
  // prints `String is: 'The String!'`
  value_consumer();
});

// Example #3: Nested scopes.
let another_string = "Another string".to_string();
scoped(&REF_TO_A_STRING, &another_string, || {
  // prints `String is: 'Another string'`
  value_consumer();
  // a nested scope.
  scoped(&REF_TO_A_STRING, my_string_ref, || {
    // prints `String is: 'The String!'`
    value_consumer();
  });
  // prints `String is: 'Another string'`
  value_consumer();
});

// Example #4: No scope (like example 1). prints `There's no string`.
value_consumer();

License

MIT OR Apache-2.0