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use std::any::{type_name, Any, TypeId};
use std::cell::{Ref, RefCell, RefMut};
use std::collections::hash_map::{Entry, HashMap};
use std::hash::{BuildHasherDefault, Hasher};
use std::ops::{Deref, DerefMut};
pub struct Resources(TypeIdMap<RefCell<Box<dyn Any>>>);
impl Default for Resources {
fn default() -> Self {
Self::new()
}
}
impl Resources {
pub fn new() -> Self {
Self(Default::default())
}
}
impl Resources {
pub fn insert<R>(&mut self, res: R)
where
R: 'static,
{
match self.0.entry(TypeId::of::<R>()) {
Entry::Vacant(entry) => entry.insert(RefCell::new(Box::new(res))),
Entry::Occupied(_) => panic!("Resource {} already present", type_name::<R>()),
};
}
pub fn clear(&mut self) {
self.0.clear();
}
}
impl Resources {
pub fn get<R>(&self) -> Res<'_, R>
where
R: 'static,
{
let ref_ = self
.0
.get(&TypeId::of::<R>())
.unwrap_or_else(|| panic!("Resource {} not present", type_name::<R>()))
.try_borrow()
.unwrap_or_else(|_err| panic!("Resource {} already borrwed", type_name::<R>()));
Res(Ref::map(ref_, |ref_| unsafe {
&*(ref_.deref() as *const dyn Any as *const R)
}))
}
pub fn get_mut<R>(&self) -> ResMut<'_, R>
where
R: 'static,
{
let ref_ = self
.0
.get(&TypeId::of::<R>())
.unwrap_or_else(|| panic!("Resource {} not present", type_name::<R>()))
.try_borrow_mut()
.unwrap_or_else(|_err| panic!("Resource {} already borrwed", type_name::<R>()));
ResMut(RefMut::map(ref_, |ref_| unsafe {
&mut *(ref_.deref_mut() as *mut dyn Any as *mut R)
}))
}
}
pub struct Res<'a, R>(Ref<'a, R>);
impl<R> Deref for Res<'_, R> {
type Target = R;
fn deref(&self) -> &R {
self.0.deref()
}
}
pub struct ResMut<'a, R>(RefMut<'a, R>);
impl<R> Deref for ResMut<'_, R> {
type Target = R;
fn deref(&self) -> &R {
self.0.deref()
}
}
impl<R> DerefMut for ResMut<'_, R> {
fn deref_mut(&mut self) -> &mut R {
self.0.deref_mut()
}
}
type TypeIdMap<V> = HashMap<TypeId, V, BuildHasherDefault<TypeIdHasher>>;
#[derive(Default)]
struct TypeIdHasher(u64);
impl Hasher for TypeIdHasher {
fn write_u64(&mut self, val: u64) {
self.0 = val;
}
fn write(&mut self, _val: &[u8]) {
unreachable!();
}
fn finish(&self) -> u64 {
self.0
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn insert_then_get() {
let mut resources = Resources::new();
resources.insert(42_u64);
let res = resources.get::<u64>();
assert_eq!(*res, 42);
}
#[test]
fn get_mut_then_get() {
let mut resources = Resources::new();
resources.insert(42_u64);
{
let mut res = resources.get_mut::<u64>();
*res = 23;
}
let res = resources.get::<u64>();
assert_eq!(*res, 23);
}
#[test]
#[should_panic]
fn insert_does_not_replace() {
let mut resources = Resources::new();
resources.insert(23_i32);
resources.insert(42_i32);
}
#[test]
fn borrows_can_be_shared() {
let mut resources = Resources::new();
resources.insert(23_i32);
let _res = resources.get::<i32>();
let _res = resources.get::<i32>();
}
#[test]
#[should_panic]
fn mutable_borrows_are_exclusive() {
let mut resources = Resources::new();
resources.insert(23_i32);
let _res = resources.get_mut::<i32>();
let _res = resources.get_mut::<i32>();
}
}