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
].
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()
.
Limitations
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
The feature "uuid"
will add support for [uuid::Uuid
].