#toggle #feature #flag #flipper


Featture toggles for Rust, extensible and with background synchronization and administration UI

7 releases

0.3.0 Jan 13, 2021
0.2.5 Oct 23, 2020
0.1.0 Sep 26, 2020

#519 in Data structures

Download history 27/week @ 2020-10-02 29/week @ 2020-10-09 25/week @ 2020-10-16 214/week @ 2020-10-23 79/week @ 2020-10-30 51/week @ 2020-11-06 28/week @ 2020-11-13 35/week @ 2020-11-20 45/week @ 2020-11-27 40/week @ 2020-12-04 19/week @ 2020-12-11 27/week @ 2020-12-18 26/week @ 2020-12-25 29/week @ 2021-01-01 78/week @ 2021-01-08 154/week @ 2021-01-15

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Used in 3 crates




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This crate is the core implementation of the feature flags (called "feattles", for short).

Its main parts are the macro [feattles!] together with the trait [Feattles]. Please refer to the main package - feattle for more information.

Usage example

use feattle_core::{feattles, Feattles};
use feattle_core::persist::NoPersistence;

// Declare the struct
feattles! {
    struct MyFeattles {
        /// Is this usage considered cool?
        is_cool: bool = true,
        /// Limit the number of "blings" available.
        /// This will not change the number of "blengs", though!
        max_blings: i32,
        /// List the actions that should not be available
        blocked_actions: Vec<String>,

// Create a new instance (`NoPersistence` is just a mock for the persistence layer)
let my_feattles = MyFeattles::new(NoPersistence);

// Read values (note the use of `*`)
assert_eq!(*my_feattles.is_cool(), true);
assert_eq!(*my_feattles.max_blings(), 0);
assert_eq!(*my_feattles.blocked_actions(), Vec::<String>::new());

How it works

The macro will generate a struct with the given name and visibility modifier (assuming private by default). The generated struct implements [Feattles] and also exposes one method for each feattle.

The methods created for each feattle allow reading their current value. For example, for a feattle is_cool: bool, there will be a method like pub fn is_cool(&self) -> MappedRwLockReadGuard<bool>. Note the use of [parking_lot::MappedRwLockReadGuard] because the interior of the struct is stored behind a RwLock to control concurrent access.

A feattle is created with the syntax $key: $type [= $default]. You can use doc coments ( starting with ///) to describe nicely what they do in your system. You can use any type that implements [FeattleValue] and optionally provide a default. If not provided, the default will be created with Default::default().

Updating values

This crate only disposes of low-level methods to load current feattles with [Feattles::reload()] and update their values with [Feattles::update()]. Please look for the crates feattle-sync and feattle-ui for higher-level functionalities.


Due to some restrictions on how the macro is written, you can only use [feattles!] once per module. For example, the following does not compile:

use feattle_core::feattles;

feattles! { struct A { } }
feattles! { struct B { } }

You can work around this limitation by creating a sub-module and then re-exporting the generated struct. Note the use of pub struct in the second case.

use feattle_core::feattles;

feattles! { struct A { } }

mod b {
    use feattle_core::feattles;
    feattles! { pub struct B { } }

use b::B;

Optional features

  • uuid: will add support for [uuid::Uuid].


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.



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