Struct SetOnce 

pub struct SetOnce<T> { /* private fields */ }

A container that can be populated at most once. Thread safe.

Once the a SetOnce is populated, it remains populated by the same object for the lifetime Self.

Invariants

• init may only increase in value.
• init may only assume values in the range 0..=2.
• init == 0 if and only if value is uninitialized.
• init == 1 if and only if there is exactly one thread with exclusive access to self.value.
• init == 2 if and only if value is initialized and valid for shared access.

Example

let value = SetOnce::new();
assert_eq!(None, value.as_ref());

let status = value.populate(42u8);
assert_eq!(true, status);
assert_eq!(Some(&42u8), value.as_ref());
assert_eq!(Some(42u8), value.copy());

let status = value.populate(101u8);
assert_eq!(false, status);
assert_eq!(Some(&42u8), value.as_ref());
assert_eq!(Some(42u8), value.copy());

Implementations

impl<T> SetOnce<T>

pub const fn new() -> Self

Create a new SetOnce.

The returned instance will be empty.

pub fn as_ref(&self) -> Option<&T>

Get a reference to the contained object.

Returns None if this SetOnce is empty.

pub fn populate(&self, value: T) -> bool

Populate the SetOnce.

Returns true if the SetOnce was successfully populated.

pub fn copy(&self) -> Option<T>

where T: Copy,

Get a copy of the contained object.

Returns None if the SetOnce is empty.

Trait Implementations

impl<T> Default for SetOnce<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Drop for SetOnce<T>

fn drop(&mut self)

Executes the destructor for this type.