Struct state::Storage
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[src]
pub struct Storage<T: Send + Sync + 'static> { /* fields omitted */ }
A single storage location for global access to a value.
A Storage
instance can hold a single value in a global context. A
Storage
instance begins without a value and must be initialized via the
set method. Once a value has been set, it can be retrieved at
any time and in any thread via the get method. The
try_get can be used to determine whether the Storage
has been initialized before attempting to retrieve the value.
For safety reasons, values stored in Storage
must be Send + Sync + 'static
.
Example
The following example uses Storage
to hold a global instance of a
HashMap
which can be modified at will:
use std::collections::HashMap; use std::sync::Mutex; use std::thread; use state::Storage; static GLOBAL_MAP: Storage<Mutex<HashMap<String, String>>> = Storage::new(); fn run_program() { let mut map = GLOBAL_MAP.get().lock().unwrap(); map.insert("another_key".into(), "another_value".into()); } fn main() { // Create the initial map and store it in `GLOBAL_MAP`. let mut initial_map = HashMap::new(); initial_map.insert("key".into(), "value".into()); GLOBAL_MAP.set(Mutex::new(initial_map)); // For illustration, we spawn a new thread that modified the map. thread::spawn(|| run_program()).join().expect("thread"); // Assert that the modification took place. let map = GLOBAL_MAP.get().lock().unwrap(); assert_eq!(map.get("another_key").unwrap(), "another_value"); }
Methods
impl<T: Send + Sync + 'static> Storage<T>
[src]
const fn new() -> Storage<T>
Create a new, uninitialized storage location.
Example
use state::Storage; static MY_GLOBAL: Storage<String> = Storage::new();
fn set(&self, value: T) -> bool
Sets the value for this storage unit to value
if it has not already
been set before.
If a value has previously been set, self
is unchanged and false
is
returned. Otherwise true
is returned.
Example
static MY_GLOBAL: Storage<&'static str> = Storage::new(); assert_eq!(MY_GLOBAL.set("Hello, world!"), true); assert_eq!(MY_GLOBAL.set("Goodbye, world!"), false);
fn try_get(&self) -> Option<&T>
Attempts to borrow the value in this storage location.
Returns Some
if the state has previously been set.
Otherwise returns None
.
Example
static MY_GLOBAL: Storage<&'static str> = Storage::new(); assert_eq!(MY_GLOBAL.try_get(), None); MY_GLOBAL.set("Hello, world!"); assert_eq!(MY_GLOBAL.try_get(), Some(&"Hello, world!"));