Implement world viewer with support for OBJ worlds

src/memory.rs

@@ -1,6 +1,7 @@
 use std::{
     collections::HashMap,
     fmt::Debug,
+    iter::FusedIterator,
     sync::{atomic::AtomicU64, Arc, Mutex, RwLock, RwLockReadGuard, TryLockError, Weak},
 };
 
@@ -117,7 +118,6 @@ impl<const N: usize, T: MemoryValue> MemoryValue for [T; N] {
 
 pub struct MemoryIter<'a, T> {
     bytes: &'a [u8],
-    index: usize,
     _phantom: std::marker::PhantomData<T>,
 }
 
@@ -125,7 +125,6 @@ impl<'a, T> MemoryIter<'a, T> {
     fn new(bytes: &'a [u8]) -> Self {
         Self {
             bytes,
-            index: 0,
             _phantom: std::marker::PhantomData,
         }
     }
@@ -136,15 +135,30 @@ impl<T: MemoryValue> Iterator for MemoryIter<'_, T> {
 
     #[inline]
     fn next(&mut self) -> Option<Self::Item> {
-        if self.index >= self.bytes.len() {
-            return None;
-        }
-        let bytes = &self.bytes[self.index..self.index + std::mem::size_of::<T>()];
-        self.index += std::mem::size_of::<T>();
+        let (bytes, rest) = self.bytes.split_at_checked(std::mem::size_of::<T>())?;
+        self.bytes = rest;
+        Some(T::from_bytes(bytes))
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let size = self.bytes.len() / std::mem::size_of::<T>();
+        (size, Some(size))
+    }
+}
+
+impl<T: MemoryValue> DoubleEndedIterator for MemoryIter<'_, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        let mid = self.bytes.len().checked_sub(std::mem::size_of::<T>())?;
+        // SAFETY: the checked_sub above is effectively a bounds check
+        let (rest, bytes) = unsafe { self.bytes.split_at_unchecked(mid) };
+        self.bytes = rest;
         Some(T::from_bytes(bytes))
     }
 }
 
+impl<T: MemoryValue> FusedIterator for MemoryIter<'_, T> {}
+
 impl MemoryRef<'_> {
     pub fn read<T: MemoryValue>(&self, index: usize) -> T {
         let from = index * size_of::<T>();