Add ArrayvecImpl, base implementation of ArrayVec

src/arrayvec_impl.rs

@@ -0,0 +1,74 @@
+use std::ptr;
+
+use crate::CapacityError;
+
+/// Implements basic arrayvec methods - based on a few required methods
+/// for length and element access.
+pub(crate) trait ArrayVecImpl {
+    type Item;
+    const CAPACITY: usize;
+
+    fn len(&self) -> usize;
+
+    unsafe fn set_len(&mut self, new_len: usize);
+
+    /// Return a slice containing all elements of the vector.
+    fn as_slice(&self) -> &[Self::Item];
+
+    /// Return a mutable slice containing all elements of the vector.
+    fn as_mut_slice(&mut self) -> &mut [Self::Item];
+
+    /// Return a raw pointer to the vector's buffer.
+    fn as_ptr(&self) -> *const Self::Item;
+
+    /// Return a raw mutable pointer to the vector's buffer.
+    fn as_mut_ptr(&mut self) -> *mut Self::Item;
+
+    fn push(&mut self, element: Self::Item) {
+        self.try_push(element).unwrap()
+    }
+
+    fn try_push(&mut self, element: Self::Item) -> Result<(), CapacityError<Self::Item>> {
+        if self.len() < Self::CAPACITY {
+            unsafe {
+                self.push_unchecked(element);
+            }
+            Ok(())
+        } else {
+            Err(CapacityError::new(element))
+        }
+    }
+
+    unsafe fn push_unchecked(&mut self, element: Self::Item) {
+        let len = self.len();
+        debug_assert!(len < Self::CAPACITY);
+        ptr::write(self.as_mut_ptr().add(len), element);
+        self.set_len(len + 1);
+    }
+
+    fn pop(&mut self) -> Option<Self::Item> {
+        if self.len() == 0 {
+            return None;
+        }
+        unsafe {
+            let new_len = self.len() - 1;
+            self.set_len(new_len);
+            Some(ptr::read(self.as_ptr().add(new_len)))
+        }
+    }
+
+    fn clear(&mut self) {
+        self.truncate(0)
+    }
+
+    fn truncate(&mut self, new_len: usize) {
+        unsafe {
+            if new_len < self.len() {
+                let tail: *mut [_] = &mut self.as_mut_slice()[new_len..];
+                self.set_len(new_len);
+                ptr::drop_in_place(tail);
+            }
+        }
+    }
+}
+