Added `SmallString<SIZE>`: `extend_from_bytes_unchecked()`: append a slice of bytes to the memory, handling re/allocation if needed.

Fortune for stack-str's current commit: Blessing − 吉

src/ext.rs

@@ -1,5 +1,18 @@
 //! Extensions
 
+pub trait Tuple2Ext<T, U>
+{
+    fn swap(self) -> (U, T);
+}
+
+impl<T, U> Tuple2Ext<T, U> for (T, U)
+{
+    #[inline(always)]
+    fn swap(self) -> (U, T) {
+	(self.1, self.0)
+    }
+}
+
 #[inline(always)] 
 pub fn is_utf8_char_boundary(byte: u8) -> bool
 {

src/small.rs

@@ -10,13 +10,12 @@ use std::{
 #[repr(C)]
 struct HeapString
 {
-    len: usize,
+    len: usize, // fill_ptr
+    // TODO: add this: cap: usize, // actual size of `data` slice
     data: NonNull<u8>, // Box<[u8]> allocated.
 }
 
-impl HeapString {
+unsafe fn unwrap_boxed_slice<T>(data: Box<[T]>) -> (usize, NonNull<T>)
-    #[inline(always)] 
-    pub unsafe fn new_from_bytes(data: Box<[u8]>) -> Self
 {
     let len = data.len();
     let data = {
@@ -26,6 +25,14 @@ impl HeapString {
 	debug_assert!(!raw.is_null(), "raw slice is null");
 	NonNull::new_unchecked(raw)
     };
+    (len, data)
+}
+
+impl HeapString {
+    #[inline(always)] 
+    pub unsafe fn new_from_bytes(data: Box<[u8]>) -> Self
+    {
+	let (len, data) = unwrap_boxed_slice(data);
 	Self {
 	    len, data
 	}
@@ -78,6 +85,48 @@ impl HeapString {
 	mem::forget(self);
 	bx
     }
+
+    /// Allocates `more` more bytes, and extends `len` by `more`.
+    ///
+    /// # Returns
+    /// Pointer to the start of the uninitialised newly allocated memory.
+    ///
+    /// # Safety
+    /// The caller must initialise the memory returned from this function call to `more` bytes.
+    #[inline(always)] 
+    unsafe fn extend_allocate(&mut self, more: usize) -> NonNull<u8>
+    {
+	let mut bx: Vec<u8> = Box::from_raw(ptr::slice_from_raw_parts_mut(self.data.as_ptr(), self.len)).into();
+	bx.reserve_exact(more);
+	debug_assert_eq!(self.len+more, bx.capacity(), "Bad reserve_exact()");
+	bx.set_len(bx.capacity());
+	bx.truncate(self.len+more);
+	
+	let (len, data) = unwrap_boxed_slice(bx.into_boxed_slice());
+	debug_assert_eq!(len, self.len+more, "Bad into_boxed_slice()");
+	self.len = len;
+	self.data = data;
+	let p = NonNull::new(self.data.as_ptr().sub(more));
+	debug_assert!(p.is_some(), "data - more == null");
+	p.unwrap_unchecked()
+    }
+
+    /// Allocates enough space to fit exactly `bytes` more data, updates `self.len`, then copies those bytes into the newly allocated memory.
+    ///
+    /// # Returns
+    /// The newly extended slice of `self`'s data now containing `bytes`.
+    ///
+    /// # Safety
+    /// The caller must guarantee that `bytes` is valid utf8.
+    #[inline(always)] 
+    unsafe fn extend_from_bytes_unchecked<'a>(&'a mut self, bytes: &[u8]) -> &'a mut [u8]
+    {
+	let len = bytes.len();
+	let end = self.extend_allocate(len);
+	ptr::copy_nonoverlapping(bytes.as_ptr(), end.as_ptr(), len);
+	slice::from_raw_parts_mut(end.as_ptr(), len)
+    }
+    //TODO: extend_from_str()
 }
 
 impl From<HeapString> for String
@@ -232,6 +281,51 @@ impl<const SIZE: usize> SmallString<SIZE>
     }
 
     //TODO: Appending, etc. Moving to heap, etc.
+    /// Moves data from `inner.stack` to `inner.heap`, returns a reference to the newly allocated `HeapString`
+    ///
+    /// # Safety
+    /// These conditions must be met or calling this is UB:
+    /// * The active discriminant is `inner.stack`.
+    /// * After this returns, the active discriminant is recognised as `inner.heap`.
+    /// * `is_allocated()` must return `true` after the operation that calls this is completed.
+    #[inline(always)] 
+    unsafe fn shunt_to_heap_unchecked(&mut self) -> &'_ mut HeapString
+    {
+	let allocated: Box<str> = self.inner.stack.as_str().into();
+	let current = &mut self.inner.heap;
+	*current = ManuallyDrop::new(HeapString::new(allocated));
+	current
+    }
+
+    /// Extends the memory inside `self` to fit more `bytes`.
+    /// The data is moved to the heap first if `self.len() + bytes.len() > SIZE`.
+    /// 
+    /// # Returns
+    /// A mutable reference to the memory inside `self` now containing the data of `bytes`.
+    ///
+    /// # Safety
+    /// The caller must ensure `bytes` is valid utf-8.
+    #[inline(always)] 
+    unsafe fn extend_from_bytes_unchecked<'i>(&'i mut self, bytes: &[u8]) -> &'i mut [u8]
+    {
+	let len = self.len();
+	if bytes.len() + len > SIZE {
+	    return self.shunt_to_heap_unchecked().extend_from_bytes_unchecked(bytes);
+	}
+	match self.inner.get_stack_mut() {
+	    Ok(stack) => {
+		let (end, fp) = (stack.buf_end(), &mut stack.fill_ptr);
+		ptr::copy_nonoverlapping(bytes.as_ptr(), end, bytes.len());
+		let slice = slice::from_raw_parts_mut(end, *fp);
+		*fp += bytes.len();
+		slice
+	    },
+	    Err(heap) => {
+		heap.extend_from_bytes_unchecked(bytes)
+	    }
+	}
+    }
+    //TODO: extend_from_str()
 }
 
 impl<const SIZE: usize> Borrow<str> for SmallString<SIZE>