pub struct JsBox<T: 'static>(/* private fields */);
Expand description
A JavaScript smart pointer object that owns Rust data.
The type JsBox<T>
provides shared ownership of a value of type T
,
allocated in the heap. The data is owned by the JavaScript engine and the
lifetime is managed by the JavaScript garbage collector.
Shared references in Rust disallow mutation by default, and JsBox
is no
exception: you cannot generally obtain a mutable reference to something
inside a JsBox
. If you need to mutate through a JsBox
, use
Cell
,
RefCell
,
or one of the other types that provide
interior mutability.
Values contained by a JsBox
must implement the Finalize
trait. Finalize::finalize
will execute with the value in a JsBox
immediately before the JsBox
is garbage
collected. If no additional finalization is necessary, an emply implementation may
be provided.
§Deref
behavior
JsBox<T>
automatically dereferences to T
(via the Deref
trait), so
you can call T
’s method on a value of type JsBox<T>
.
let vec: Handle<JsBox<Vec<_>>> = cx.boxed(vec![1, 2, 3]);
println!("Length: {}", vec.len());
§Examples
Passing some immutable data between Rust and JavaScript.
fn create_path(mut cx: FunctionContext) -> JsResult<JsBox<PathBuf>> {
let path = cx.argument::<JsString>(0)?.value(&mut cx);
let path = Path::new(&path).to_path_buf();
Ok(cx.boxed(path))
}
fn print_path(mut cx: FunctionContext) -> JsResult<JsUndefined> {
let path = cx.argument::<JsBox<PathBuf>>(0)?;
println!("{}", path.display());
Ok(cx.undefined())
}
Passing a user defined struct wrapped in a RefCell
for mutability. This
pattern is useful for creating classes in JavaScript.
type BoxedPerson = JsBox<RefCell<Person>>;
struct Person {
name: String,
}
impl Finalize for Person {}
impl Person {
pub fn new(name: String) -> Self {
Person { name }
}
pub fn set_name(&mut self, name: String) {
self.name = name;
}
pub fn greet(&self) -> String {
format!("Hello, {}!", self.name)
}
}
fn person_new(mut cx: FunctionContext) -> JsResult<BoxedPerson> {
let name = cx.argument::<JsString>(0)?.value(&mut cx);
let person = RefCell::new(Person::new(name));
Ok(cx.boxed(person))
}
fn person_set_name(mut cx: FunctionContext) -> JsResult<JsUndefined> {
let person = cx.argument::<BoxedPerson>(0)?;
let mut person = person.borrow_mut();
let name = cx.argument::<JsString>(1)?.value(&mut cx);
person.set_name(name);
Ok(cx.undefined())
}
fn person_greet(mut cx: FunctionContext) -> JsResult<JsString> {
let person = cx.argument::<BoxedPerson>(0)?;
let person = person.borrow();
let greeting = person.greet();
Ok(cx.string(greeting))
}
Implementations§
source§impl<T: Finalize + 'static> JsBox<T>
impl<T: Finalize + 'static> JsBox<T>
Values contained by a JsBox
must be Finalize + 'static
§Finalize
The sys::prelude::Finalize
trait provides a finalize
method that will be called
immediately before the JsBox
is garbage collected.
§`‘static’
The lifetime of a JsBox
is managed by the JavaScript garbage collector. Since Rust
is unable to verify the lifetime of the contents, references must be valid for the
entire duration of the program. This does not mean that the JsBox
will be valid
until the application terminates, only that its lifetime is indefinite.
Trait Implementations§
source§impl<T: 'static> Object for JsBox<T>
impl<T: 'static> Object for JsBox<T>
source§fn get_opt<'a, V: Value, C: Context<'a>, K: PropertyKey>(
&self,
cx: &mut C,
key: K
) -> NeonResult<Option<Handle<'a, V>>>
fn get_opt<'a, V: Value, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K ) -> NeonResult<Option<Handle<'a, V>>>
undefined
and
attempts to downcast the value if it existed.source§fn get_value<'a, C: Context<'a>, K: PropertyKey>(
&self,
cx: &mut C,
key: K
) -> NeonResult<Handle<'a, JsValue>>
fn get_value<'a, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K ) -> NeonResult<Handle<'a, JsValue>>
source§fn get<'a, V: Value, C: Context<'a>, K: PropertyKey>(
&self,
cx: &mut C,
key: K
) -> NeonResult<Handle<'a, V>>
fn get<'a, V: Value, C: Context<'a>, K: PropertyKey>( &self, cx: &mut C, key: K ) -> NeonResult<Handle<'a, V>>
obj.get_value(&mut cx)?.downcast_or_throw(&mut cx)
. Read moresource§fn get_own_property_names<'a, C: Context<'a>>(
&self,
cx: &mut C
) -> JsResult<'a, JsArray>
fn get_own_property_names<'a, C: Context<'a>>( &self, cx: &mut C ) -> JsResult<'a, JsArray>
napi-6
only.