Struct Callback

pub struct Callback<EVENT, MSG>(/* private fields */);

A generic sized representation of a function that can be attached to a Node. The callback will essentially be owned by the element

Limitations: The callback takes an Fn instead of FnMut, therefore it can not mutate the environment variables

In effect callbacks attached to DOM events are limited to only passing an MSG to the program and not complex statements.

Note: It would have been nice to have the inner value be Rc<FnMut(EVENT) -> MSG> +'a but there are a lot of issues that this becomes infeasible: 1 - wasm_bindgen::Closure requires that ’static references to the closure 2 - Accessing Rc::get_mut requires that there is no other Rc or Weak references else where. - We could be iterating on the elements for recursively setting the attributes which is not allowed to have recursive mutable iteration - Attributes of the same name are merged therefore cloning the attributes, hence the callback is necessary.

Implementations

impl<EVENT, MSG> Callback<EVENT, MSG>

where EVENT: 'static, MSG: 'static,

pub fn emit<T>(&self, value: T) -> MSG

where T: Into<EVENT>,

This method calls the actual callback.

pub fn map_callback<MSG2>( self, cb: Callback<MSG, MSG2>, ) -> Callback<EVENT, MSG2>

where MSG2: 'static,

map this callback using another callback such that MSG becomes MSG2

Trait Implementations

impl<EVENT, MSG> Clone for Callback<EVENT, MSG>

Note: using the #[derive(Clone)] needs EVENT and MSG to also be Clone

The reason this is manually implemented is, so that EVENT and MSG doesn’t need to be Clone as it is part of the Callback objects and cloning here is just cloning the pointer of the actual callback function

fn clone(&self) -> Callback<EVENT, MSG>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<EVENT, MSG> Debug for Callback<EVENT, MSG>

Note: using the #[derive(Debug)] needs EVENT and MSG to also be Debug

The reason this is manually implemented is, so that EVENT and MSG doesn’t need to be Debug as it is part of the Callback objects and are not shown.

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

Formats the value using the given formatter.

impl<EVENT, F, MSG> From<F> for Callback<EVENT, MSG>

where F: Fn(EVENT) -> MSG + 'static,

fn from(func: F) -> Callback<EVENT, MSG>

Converts to this type from the input type.

impl<EVENT, MSG> PartialEq for Callback<EVENT, MSG>

Note: using the #[derive(PartialEq)] needs EVENT and MSG to also be PartialEq.

The reason this is manually implemented is, so that EVENT and MSG doesn’t need to be PartialEq as it is part of the Callback objects and are not compared

Note: There is no 2 closures are equal, even if they are logically the same. We return true here so as to not make a diff for the callback attribute. Replacing the callback function for each view call is in-efficient.

fn eq(&self, _rhs: &Callback<EVENT, MSG>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.