16 releases (4 breaking)
0.5.1 | Feb 1, 2024 |
---|---|
0.5.0 | Feb 1, 2024 |
0.4.4 | Jan 28, 2024 |
0.3.1 | Jan 28, 2024 |
0.1.0 | Nov 11, 2023 |
#583 in Algorithms
226 downloads per month
Used in j-pls
12KB
183 lines
Lazy non-const Statics
This crate provides a simple global allocation item to store items as statics that arent necessarily constant. "Global" is a bit of a misnomer, as these are more accurately described as immutable non-constant statics.
Global
dereferences to T
, so it can be treated as a wrapper that allows any type to be static.
Usage
Global
stores a function pointer that produces T
. On the first deref call, this value will be
produced and allocated on the heap for the lifetime of the program. Subsequent calls will return
this cached value.
use global_static::Global;
static MY_NUM: Global<i32> = Global::new(|| 5);
fn main() {
assert_eq!(*MY_NUM + 5, 10);
}
ctor Feature
If you use the ctor
feature flag, a macro is provided to initalize a global on startup.
use global_static::ctor_static;
ctor_static! {
MY_NUM: i32 = { 5 };
MY_OTHER_NUM: i32 = { *MY_NUM * 2 };
};
singleton Feature
Most usecases for Global
involve a struct that is parsed and then placed in a static like so:
use global_static::Global;
pub static CONFIG: Global<Config> = Global::new(Default::default);
pub struct Config {
name: String
}
impl Default for Config {
fn default() -> Self { /* implementation */ }
}
The singleton
attribute generates a static item for a given struct.
use global_static::singleton;
#[singleton] //generates the CONFIG static
pub struct Config {
name: String
}
impl Default for Config {
fn default() -> Self { /* implementation */ }
}
Limitations
The biggest limitation is the double-pointer indirection that arises from storing a type that
itself allocates memory, such as Vec
or Box
. It also isn't possible to store DSTs, as the
data needs to be returned from a function on the stack. This could be fixed with a type that
offsets its allocation onto the producing closure, however types like Vec
that require extra
information would still not work with this system.
Dependencies
~97KB