added iterator functions

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "stackalloc"
-version = "1.0.1"
+version = "1.1.0"
 homepage = "https://git.flanchan.moe/flanchan/stackalloc-rs"
 repository = "https://github.com/notflan/stackalloc-rs"
 keywords = ["alloca", "stack", "stack-allocation", "safe"]

src/avec.rs

@@ -90,7 +90,7 @@ impl<'a, T> AVec<'a, T>
     /// Have the elements been moved to the heap?
     pub fn is_allocated(&self) -> bool
     {
-	self.fill_ptr() > self.stack_sz
+	self.fill_ptr() >= self.stack_sz
     }
     
     /// Create a new `AVec` with this backing buffer.
@@ -109,4 +109,52 @@ impl<'a, T> AVec<'a, T>
 	    _stack: PhantomData
 	}
     }
+
+    fn move_to_heap(&mut self)
+    {
+	let buf: Vec<T> = unsafe {
+	    slice::from_raw_parts(self.inner.stack.buf_ptr as *const MaybeUninit<T>, self.fill_ptr()).iter().map(|x| x.as_ptr().read()).collect()
+	};
+	self.inner = Internal {
+	    heap: ManuallyDrop::new(HeapBuffer {
+		_fill_ptr: self.stack_sz,
+		buf,
+	    }),
+	};
+    }
+    
+    /// Insert an element into this `AVec`.
+    pub fn push(&mut self, item: T)
+    {
+	if self.is_allocated()
+	{
+	    unsafe {
+		(*self.inner.heap).buf.push(item)
+	    }
+	} else {
+	    unsafe {
+		let ptr = self.inner.stack.fill_ptr;
+		*self.inner.stack.buf_ptr.add(ptr) = MaybeUninit::new(item);
+		self.inner.stack.fill_ptr += 1;
+
+		if self.is_allocated() {
+		    // Move all items to heap
+		    self.move_to_heap();
+		}
+	    }
+	}
+    }
+
+    /// The number of elements in this `AVec`.
+    pub fn len(&self) -> usize
+    {
+	if self.is_allocated()
+	{
+	    unsafe {
+		self.inner.heap.buf.len()
+	    }
+	} else {
+	    self.fill_ptr()
+	}
+    }
 }

src/lib.rs

@@ -106,7 +106,7 @@ use std::{
     ptr,
 };
 
-//TODO: pub mod avec; pub use avec::AVec;
+pub mod avec; pub use avec::AVec;
 mod ffi;
 
 /// Allocate a runtime length uninitialised byte buffer on the stack, call `callback` with this buffer, and then deallocate the buffer.
@@ -305,5 +305,79 @@ T: Default
     stackalloc_with(size, T::default, callback)
 }
 
+
+/// Collect an iterator into a stack allocated buffer up to `size` elements, call `callback` with this buffer, and then drop and deallocate the buffer.
+///
+/// See `stackalloc()`.
+///
+/// # Size
+/// We will only take up to `size` elements from the iterator, the rest of the iterator is dropped.
+/// If the iterator yield less elements than `size`, then the slice passed to callback will be smaller than `size` and only contain the elements actually yielded.
+#[inline] pub fn stackalloc_with_iter<I, T, U, F>(size: usize, iter: I, callback: F) -> U
+where F: FnOnce(&mut [T]) -> U,
+      I: IntoIterator<Item = T>,
+{
+    stackalloc_uninit(size, move |buf| {
+	let mut done = 0;
+	for (d, s) in buf.iter_mut().zip(iter.into_iter())
+	{
+	    *d = MaybeUninit::new(s);
+	    done+=1;
+	}
+	// SAFETY: We just initialised `done` elements of `buf` above.
+	let buf = unsafe {
+	    slice_assume_init_mut(&mut buf[..done])
+	};
+	let ret = callback(buf);	
+	if mem::needs_drop::<T>()
+	{
+	    // SAFETY: We have initialised the `buf` above
+	    unsafe {
+		ptr::drop_in_place(buf as *mut _);
+	    }
+	}
+	ret
+    })
+}
+
+/// Collect an exact size iterator into a stack allocated slice, call `callback` with this buffer, and then drop and deallocate the buffer.
+///
+/// See `stackalloc_with_iter()`.
+///
+/// # Size
+/// If the implementation of `ExactSizeIterator` on `I` is incorrect and reports a longer length than the iterator actually produces, then the slice passed to `callback` is shortened to the number of elements actually produced.
+#[inline] pub fn stackalloc_from_iter_exact<I, T, U, F>(iter: I, callback: F) -> U
+where F: FnOnce(&mut [T]) -> U,
+      I: IntoIterator<Item = T>,
+      I::IntoIter: ExactSizeIterator,
+{
+    let iter = iter.into_iter();
+    stackalloc_with_iter(iter.len(), iter, callback)
+}
+
+/// Collect an iterator into a stack allocated buffer, call `callback` with this buffer, and then drop and deallocate the buffer.
+///
+/// # Safety
+/// While the slice passed to `callback` is guaranteed to be safe to use, regardless of if the iterator fills (or tries to overfill) it,  this function is still marked as `unsafe` because it trusts the iterator `I` reports an accurate length with its `size_hint()`.
+/// It is recommended to instead use `stackalloc_with_iter()` specifying a strict upper bound on the buffer's size, or `stackalloc_from_iter_exact()` for `ExactSizeIterator`s, as this function may allocate far more, or far less (even 0) memory needed to hold all the iterator's elements; therefore this function will very easily not work properly and/or cause stack overflow if used carelessly.
+///
+/// If the standard library's `std::iter::TrustedLen` trait becomes stablised, this function will be changed to require that as a bound on `I` and this function will no longer be `unsafe`.
+///
+/// # Size
+/// The size allocated for the buffer will be the upper bound of the iterator's `size_hint()` if one exists. If not, then the size allocated will be the lower bound of `size_hint()`.
+/// This can potentially result in only some of the iterator being present in the buffer, or the buffer allocated being much larger than the iterator itself. 
+/// If this iterator does not have a good `size_hint()` for this purpose, use `stackalloc_with_iter()`, or `stackalloc_from_iter_exact()` if the iterator has an exact size.
+#[inline] pub unsafe fn stackalloc_from_iter_trusted<I, T, U, F>(iter: I, callback: F) -> U
+where F: FnOnce(&mut [T]) -> U,
+      I: IntoIterator<Item = T>,
+{
+    let iter = iter.into_iter();
+    stackalloc_with_iter(match iter.size_hint() {
+	(_, Some(x)) |
+	(x, _) => x,
+    }, iter, callback)
+}
+
+
 #[cfg(test)]
 mod tests;

src/tests.rs

@@ -1,5 +1,37 @@
 //! Contains tests and benchmarks
 
+#[test]
+fn unknown_size_iter()
+{
+    let iter = 10..;
+    let result: u64 = iter.clone().take(10).sum();
+
+    assert_eq!(result, super::stackalloc_with_iter(10, iter, |buf| buf.iter().copied().sum::<u64>()));
+}
+
+fn unknown_size_iter_len() {
+    assert_eq!(super::stackalloc_with_iter(1024, 0..100, |buf| buf.len()), 100);
+}
+
+#[test]
+fn exact_size_iter()
+{
+    let iter = vec![
+	1,
+	2,
+	13,
+	24,
+	100,
+    ];
+    let len = iter.len();
+    let result: u64 = iter.iter().copied().sum();
+
+    assert_eq!(super::stackalloc_from_iter_exact(iter, |buf| {
+	assert_eq!(buf.len(), len);
+	buf.iter().copied().sum::<u64>()
+    }), result);
+}
+
 #[test]
 #[should_panic]
 fn unwinding_over_boundary()