Struct js_sys::Promise

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pub struct Promise { /* private fields */ }
Expand description

The Promise object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.

MDN documentation

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impl Promise

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pub fn new(cb: &mut dyn FnMut(Function, Function)) -> Promise

Creates a new Promise with the provided executor cb

The cb is a function that is passed with the arguments resolve and reject. The cb function is executed immediately by the Promise implementation, passing resolve and reject functions (the executor is called before the Promise constructor even returns the created object). The resolve and reject functions, when called, resolve or reject the promise, respectively. The executor normally initiates some asynchronous work, and then, once that completes, either calls the resolve function to resolve the promise or else rejects it if an error occurred.

If an error is thrown in the executor function, the promise is rejected. The return value of the executor is ignored.

MDN documentation

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impl Promise

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pub fn all(obj: &JsValue) -> Promise

The Promise.all(iterable) method returns a single Promise that resolves when all of the promises in the iterable argument have resolved or when the iterable argument contains no promises. It rejects with the reason of the first promise that rejects.

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impl Promise

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pub fn all_settled(obj: &JsValue) -> Promise

The Promise.allSettled(iterable) method returns a single Promise that resolves when all of the promises in the iterable argument have either fulfilled or rejected or when the iterable argument contains no promises.

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impl Promise

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pub fn any(obj: &JsValue) -> Promise

The Promise.any(iterable) method returns a single Promise that resolves when any of the promises in the iterable argument have resolved or when the iterable argument contains no promises. It rejects with an AggregateError if all promises in the iterable rejected.

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impl Promise

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pub fn race(obj: &JsValue) -> Promise

The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.

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impl Promise

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pub fn reject(obj: &JsValue) -> Promise

The Promise.reject(reason) method returns a Promise object that is rejected with the given reason.

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impl Promise

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pub fn resolve(obj: &JsValue) -> Promise

The Promise.resolve(value) method returns a Promise object that is resolved with the given value. If the value is a promise, that promise is returned; if the value is a thenable (i.e. has a “then” method), the returned promise will “follow” that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value.

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impl Promise

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pub fn catch(&self, cb: &Closure<dyn FnMut(JsValue)>) -> Promise

The catch() method returns a Promise and deals with rejected cases only. It behaves the same as calling Promise.prototype.then(undefined, onRejected) (in fact, calling obj.catch(onRejected) internally calls obj.then(undefined, onRejected)).

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impl Promise

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pub fn then(&self, cb: &Closure<dyn FnMut(JsValue)>) -> Promise

The then() method returns a Promise. It takes up to two arguments: callback functions for the success and failure cases of the Promise.

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impl Promise

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pub fn then2( &self, resolve: &Closure<dyn FnMut(JsValue)>, reject: &Closure<dyn FnMut(JsValue)>, ) -> Promise

Same as then, only with both arguments provided.

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impl Promise

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pub fn finally(&self, cb: &Closure<dyn FnMut()>) -> Promise

The finally() method returns a Promise. When the promise is settled, whether fulfilled or rejected, the specified callback function is executed. This provides a way for code that must be executed once the Promise has been dealt with to be run whether the promise was fulfilled successfully or rejected.

This lets you avoid duplicating code in both the promise’s then() and catch() handlers.

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Methods from Deref<Target = Object>§

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pub fn constructor(&self) -> Function

The constructor property returns a reference to the Object constructor function that created the instance object.

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pub fn has_own_property(&self, property: &JsValue) -> bool

The hasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

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pub fn is_prototype_of(&self, value: &JsValue) -> bool

The isPrototypeOf() method checks if an object exists in another object’s prototype chain.

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pub fn property_is_enumerable(&self, property: &JsValue) -> bool

The propertyIsEnumerable() method returns a Boolean indicating whether the specified property is enumerable.

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pub fn to_locale_string(&self) -> JsString

The toLocaleString() method returns a string representing the object. This method is meant to be overridden by derived objects for locale-specific purposes.

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pub fn to_string(&self) -> JsString

The toString() method returns a string representing the object.

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pub fn value_of(&self) -> Object

The valueOf() method returns the primitive value of the specified object.

MDN documentation

Methods from Deref<Target = JsValue>§

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pub const NULL: JsValue = _

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pub const UNDEFINED: JsValue = _

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pub const TRUE: JsValue = _

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pub const FALSE: JsValue = _

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pub fn as_f64(&self) -> Option<f64>

Returns the f64 value of this JS value if it’s an instance of a number.

If this JS value is not an instance of a number then this returns None.

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pub fn is_string(&self) -> bool

Tests whether this JS value is a JS string.

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pub fn as_string(&self) -> Option<String>

If this JS value is a string value, this function copies the JS string value into wasm linear memory, encoded as UTF-8, and returns it as a Rust String.

To avoid the copying and re-encoding, consider the JsString::try_from() function from js-sys instead.

If this JS value is not an instance of a string or if it’s not valid utf-8 then this returns None.

§UTF-16 vs UTF-8

JavaScript strings in general are encoded as UTF-16, but Rust strings are encoded as UTF-8. This can cause the Rust string to look a bit different than the JS string sometimes. For more details see the documentation about the str type which contains a few caveats about the encodings.

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pub fn as_bool(&self) -> Option<bool>

Returns the bool value of this JS value if it’s an instance of a boolean.

If this JS value is not an instance of a boolean then this returns None.

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pub fn is_null(&self) -> bool

Tests whether this JS value is null

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pub fn is_undefined(&self) -> bool

Tests whether this JS value is undefined

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pub fn is_symbol(&self) -> bool

Tests whether the type of this JS value is symbol

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pub fn is_object(&self) -> bool

Tests whether typeof self == "object" && self !== null.

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pub fn is_array(&self) -> bool

Tests whether this JS value is an instance of Array.

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pub fn is_function(&self) -> bool

Tests whether the type of this JS value is function.

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pub fn is_bigint(&self) -> bool

Tests whether the type of this JS value is bigint.

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pub fn js_typeof(&self) -> JsValue

Applies the unary typeof JS operator on a JsValue.

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pub fn js_in(&self, obj: &JsValue) -> bool

Applies the binary in JS operator on the two JsValues.

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pub fn is_truthy(&self) -> bool

Tests whether the value is “truthy”.

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pub fn is_falsy(&self) -> bool

Tests whether the value is “falsy”.

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pub fn loose_eq(&self, other: &JsValue) -> bool

Compare two JsValues for equality, using the == operator in JS.

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pub fn bit_not(&self) -> JsValue

Applies the unary ~ JS operator on a JsValue.

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pub fn unsigned_shr(&self, rhs: &JsValue) -> u32

Applies the binary >>> JS operator on the two JsValues.

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pub fn checked_div(&self, rhs: &JsValue) -> JsValue

Applies the binary / JS operator on two JsValues, catching and returning any RangeError thrown.

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pub fn pow(&self, rhs: &JsValue) -> JsValue

Applies the binary ** JS operator on the two JsValues.

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pub fn lt(&self, other: &JsValue) -> bool

Applies the binary < JS operator on the two JsValues.

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pub fn le(&self, other: &JsValue) -> bool

Applies the binary <= JS operator on the two JsValues.

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pub fn ge(&self, other: &JsValue) -> bool

Applies the binary >= JS operator on the two JsValues.

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pub fn gt(&self, other: &JsValue) -> bool

Applies the binary > JS operator on the two JsValues.

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pub fn unchecked_into_f64(&self) -> f64

Applies the unary + JS operator on a JsValue. Can throw.

MDN documentation

Trait Implementations§

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impl AsRef<JsValue> for Promise

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fn as_ref(&self) -> &JsValue

Converts this type into a shared reference of the (usually inferred) input type.
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impl AsRef<Object> for Promise

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fn as_ref(&self) -> &Object

Converts this type into a shared reference of the (usually inferred) input type.
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impl AsRef<Promise> for Promise

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fn as_ref(&self) -> &Promise

Converts this type into a shared reference of the (usually inferred) input type.
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impl Clone for Promise

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fn clone(&self) -> Promise

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Promise

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Deref for Promise

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type Target = Object

The resulting type after dereferencing.
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fn deref(&self) -> &Object

Dereferences the value.
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impl From<JsValue> for Promise

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fn from(obj: JsValue) -> Promise

Converts to this type from the input type.
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impl From<Promise> for JsValue

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fn from(obj: Promise) -> JsValue

Converts to this type from the input type.
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impl From<Promise> for Object

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fn from(obj: Promise) -> Object

Converts to this type from the input type.
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impl FromWasmAbi for Promise

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type Abi = <JsValue as FromWasmAbi>::Abi

The wasm ABI type that this converts from when coming back out from the ABI boundary.
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unsafe fn from_abi(js: Self::Abi) -> Self

Recover a Self from Self::Abi. Read more
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impl<'a> IntoWasmAbi for &'a Promise

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type Abi = <&'a JsValue as IntoWasmAbi>::Abi

The wasm ABI type that this converts into when crossing the ABI boundary.
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fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.
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impl IntoWasmAbi for Promise

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type Abi = <JsValue as IntoWasmAbi>::Abi

The wasm ABI type that this converts into when crossing the ABI boundary.
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fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.
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impl JsCast for Promise

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fn instanceof(val: &JsValue) -> bool

Performs a dynamic instanceof check to see whether the JsValue provided is an instance of this type. Read more
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fn unchecked_from_js(val: JsValue) -> Self

Performs a zero-cost unchecked conversion from a JsValue into an instance of Self Read more
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fn unchecked_from_js_ref(val: &JsValue) -> &Self

Performs a zero-cost unchecked conversion from a &JsValue into an instance of &Self. Read more
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fn has_type<T>(&self) -> bool
where T: JsCast,

Test whether this JS value has a type T. Read more
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fn dyn_into<T>(self) -> Result<T, Self>
where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T. Read more
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fn dyn_ref<T>(&self) -> Option<&T>
where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T. Read more
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fn unchecked_into<T>(self) -> T
where T: JsCast,

Performs a zero-cost unchecked cast into the specified type. Read more
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fn unchecked_ref<T>(&self) -> &T
where T: JsCast,

Performs a zero-cost unchecked cast into a reference to the specified type. Read more
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fn is_instance_of<T>(&self) -> bool
where T: JsCast,

Test whether this JS value is an instance of the type T. Read more
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fn is_type_of(val: &JsValue) -> bool

Performs a dynamic check to see whether the JsValue provided is a value of this type. Read more
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impl LongRefFromWasmAbi for Promise

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type Abi = <JsValue as LongRefFromWasmAbi>::Abi

Same as RefFromWasmAbi::Abi
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type Anchor = Promise

Same as RefFromWasmAbi::Anchor
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unsafe fn long_ref_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi
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impl OptionFromWasmAbi for Promise

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fn is_none(abi: &Self::Abi) -> bool

Tests whether the argument is a “none” instance. If so it will be deserialized as None, and otherwise it will be passed to FromWasmAbi.
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impl<'a> OptionIntoWasmAbi for &'a Promise

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fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option. Read more
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impl OptionIntoWasmAbi for Promise

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fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option. Read more
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impl RefFromWasmAbi for Promise

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type Abi = <JsValue as RefFromWasmAbi>::Abi

The wasm ABI type references to Self are recovered from.
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type Anchor = ManuallyDrop<Promise>

The type that holds the reference to Self for the duration of the invocation of the function that has an &Self parameter. This is required to ensure that the lifetimes don’t persist beyond one function call, and so that they remain anonymous.
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unsafe fn ref_from_abi(js: Self::Abi) -> Self::Anchor

Recover a Self::Anchor from Self::Abi. Read more
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impl WasmDescribe for Promise

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ReturnWasmAbi for T
where T: IntoWasmAbi,

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type Abi = <T as IntoWasmAbi>::Abi

Same as IntoWasmAbi::Abi
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fn return_abi(self) -> <T as ReturnWasmAbi>::Abi

Same as IntoWasmAbi::into_abi, except that it may throw and never return in the case of Err.
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> VectorFromWasmAbi for T
where T: JsObject,

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impl<T> VectorIntoWasmAbi for T
where T: JsObject,