dioxus/packages/core/src/scope.rs

use crate::nodes::VNode;
use crate::prelude::*;
use bumpalo::Bump;
use std::{
    any::TypeId, cell::RefCell, future::Future, marker::PhantomData, sync::atomic::AtomicUsize,
};

/// Every component in Dioxus is represented by a `Scope`.
///
/// Scopes contain the state for hooks, the component's props, and other lifecycle information.
///
/// Scopes are allocated in a generational arena. As components are mounted/unmounted, they will replace slots of dead components.
/// The actual contents of the hooks, though, will be allocated with the standard allocator. These should not allocate as frequently.
pub struct Scope {
    // These hooks are actually references into the hook arena
    // These two could be combined with "OwningRef" to remove unsafe usage
    // TODO @Jon
    hooks: RefCell<Vec<*mut Hook>>,
    hook_arena: typed_arena::Arena<Hook>,

    props_type: TypeId,
    caller: *const i32,
}

impl Scope {
    // create a new scope from a function
    pub fn new<T: 'static>(f: FC<T>) -> Self {
        // Capture the props type
        let props_type = TypeId::of::<T>();
        let arena = typed_arena::Arena::new();
        let hooks = RefCell::new(Vec::new());

        let caller = f as *const i32;

        Self {
            hook_arena: arena,
            hooks,
            props_type,
            caller,
        }
    }

    pub fn create_context<T: Properties>(&mut self) -> Context<T> {
        Context {
            _p: PhantomData {},
            arena: &self.hook_arena,
            hooks: &self.hooks,
            idx: 0.into(),
            props: T::new(),
        }
    }

    /// Create a new context and run the component with references from the Virtual Dom
    /// This function downcasts the function pointer based on the stored props_type
    fn run<T: 'static>(&self, f: FC<T>) {}

    fn call<T: Properties + 'static>(&mut self, val: T) {
        if self.props_type == TypeId::of::<T>() {
            /*
            SAFETY ALERT

            This particular usage of transmute is outlined in its docs https://doc.rust-lang.org/std/mem/fn.transmute.html
            We hide the generic bound on the function item by casting it to raw pointer. When the function is actually called,
            we transmute the function back using the props as reference.

            This is safe because we check that the generic type matches before casting.
            */
            let caller = unsafe { std::mem::transmute::<*const i32, FC<T>>(self.caller) };
            let ctx = self.create_context::<T>();
            // TODO: do something with these nodes
            let nodes = caller(ctx);
        } else {
            panic!("Do not try to use `call` on Scopes with the wrong props type")
        }
    }
}

pub struct Hook(pub Box<dyn std::any::Any>);

impl Hook {
    pub fn new(state: Box<dyn std::any::Any>) -> Self {
        Self(state)
    }
}