From 7936744b2dc7787e4290ab9dfe2fc0d6b144b27a Mon Sep 17 00:00:00 2001
From: Alexey Gerasev <alexey.gerasev@gmail.com>
Date: Sun, 3 Mar 2024 11:22:24 +0700
Subject: [PATCH] Provide const constructor for array rb

---
 Cargo.toml       |  4 ++--
 src/rb/local.rs  |  7 ++++---
 src/rb/macros.rs |  7 ++++++-
 src/rb/shared.rs |  5 +++--
 src/storage.rs   |  5 +++++
 src/tests/new.rs |  3 +++
 src/utils.rs     | 21 ++++++++++-----------
 7 files changed, 33 insertions(+), 19 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 90d3f32..94d5fdc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,14 +7,14 @@ readme = "README.md"
 license = "MIT/Apache-2.0"
 
 [workspace.dependencies]
-ringbuf = { path = ".", version = "0.4.0-rc.2" }
+ringbuf = { path = ".", version = "0.4.0-rc.4" }
 
 [workspace]
 members = ["async", "blocking"]
 
 [package]
 name = "ringbuf"
-version = "0.4.0-rc.3"
+version = "0.4.0-rc.4"
 edition.workspace = true
 authors.workspace = true
 description = "Lock-free SPSC FIFO ring buffer with direct access to inner data"
diff --git a/src/rb/local.rs b/src/rb/local.rs
index 1145d52..c2d383e 100644
--- a/src/rb/local.rs
+++ b/src/rb/local.rs
@@ -25,7 +25,7 @@ struct End {
 }
 
 impl End {
-    fn new(index: usize) -> Self {
+    const fn new(index: usize) -> Self {
         Self {
             index: Cell::new(index),
             held: Cell::new(false),
@@ -49,8 +49,9 @@ impl<S: Storage> LocalRb<S> {
     ///
     /// The items in storage inside `read..write` range must be initialized, items outside this range must be uninitialized.
     /// `read` and `write` positions must be valid (see implementation details).
-    pub unsafe fn from_raw_parts(storage: S, read: usize, write: usize) -> Self {
-        assert!(!storage.is_empty());
+    ///
+    /// `storage` length must be non-zero.
+    pub const unsafe fn from_raw_parts(storage: S, read: usize, write: usize) -> Self {
         Self {
             storage,
             read: End::new(read),
diff --git a/src/rb/macros.rs b/src/rb/macros.rs
index 26251d3..8b698b6 100644
--- a/src/rb/macros.rs
+++ b/src/rb/macros.rs
@@ -2,7 +2,12 @@ macro_rules! rb_impl_init {
     ($type:ident) => {
         impl<T, const N: usize> Default for $type<crate::storage::Array<T, N>> {
             fn default() -> Self {
-                unsafe { Self::from_raw_parts(crate::utils::uninit_array().into(), usize::default(), usize::default()) }
+                Self::new()
+            }
+        }
+        impl<T, const N: usize> $type<crate::storage::Array<T, N>> {
+            pub const fn new() -> Self {
+                unsafe { Self::from_raw_parts(crate::storage::Array::new(crate::utils::uninit_array()), 0, 0) }
             }
         }
 
diff --git a/src/rb/shared.rs b/src/rb/shared.rs
index c73cba6..36cad99 100644
--- a/src/rb/shared.rs
+++ b/src/rb/shared.rs
@@ -59,8 +59,9 @@ impl<S: Storage> SharedRb<S> {
     ///
     /// The items in storage inside `read..write` range must be initialized, items outside this range must be uninitialized.
     /// `read` and `write` positions must be valid (see implementation details).
-    pub unsafe fn from_raw_parts(storage: S, read: usize, write: usize) -> Self {
-        assert!(!storage.is_empty());
+    ///
+    /// `storage` length must be non-zero.
+    pub const unsafe fn from_raw_parts(storage: S, read: usize, write: usize) -> Self {
         Self {
             storage,
             read_index: CachePadded::new(AtomicUsize::new(read)),
diff --git a/src/storage.rs b/src/storage.rs
index 891af01..430cb88 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -93,6 +93,11 @@ pub struct Owning<T: ?Sized> {
 unsafe impl<T: ?Sized> Sync for Owning<T> where T: Sync {}
 impl<T> From<T> for Owning<T> {
     fn from(value: T) -> Self {
+        Self::new(value)
+    }
+}
+impl<T> Owning<T> {
+    pub const fn new(value: T) -> Self {
         Self {
             data: UnsafeCell::new(value),
         }
diff --git a/src/tests/new.rs b/src/tests/new.rs
index 7c17f3f..4cf6dda 100644
--- a/src/tests/new.rs
+++ b/src/tests/new.rs
@@ -3,6 +3,9 @@ use crate::{storage::Array, traits::*};
 #[cfg(feature = "alloc")]
 use alloc::vec::Vec;
 
+#[allow(clippy::declare_interior_mutable_const)]
+const _RB: Rb<Array<i32, 4>> = Rb::<Array<i32, 4>>::new();
+
 #[test]
 fn new_static() {
     let rb = Rb::<Array<i32, 2>>::default();
diff --git a/src/utils.rs b/src/utils.rs
index e70e05b..14fb185 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -6,7 +6,7 @@ use core::{
 };
 
 // TODO: Remove on `maybe_uninit_uninit_array` stabilization.
-pub fn uninit_array<T, const N: usize>() -> [MaybeUninit<T>; N] {
+pub const fn uninit_array<T, const N: usize>() -> [MaybeUninit<T>; N] {
     unsafe { MaybeUninit::<[MaybeUninit<T>; N]>::uninit().assume_init() }
 }
 
@@ -39,21 +39,20 @@ pub fn move_uninit_slice<T>(dst: &mut [MaybeUninit<T>], src: &[MaybeUninit<T>])
 }
 
 pub fn array_to_uninit<T, const N: usize>(value: [T; N]) -> [MaybeUninit<T>; N] {
-    let value = mem::ManuallyDrop::new(value);
-    let ptr = &value as *const _ as *const [MaybeUninit<T>; N];
-    unsafe { ptr.read() }
+    let value = MaybeUninit::new(value);
+    let this = &value as *const _ as *const [MaybeUninit<T>; N];
+    unsafe { this.read() }
 }
 
 #[cfg(feature = "alloc")]
-pub fn vec_to_uninit<T>(value: Vec<T>) -> Vec<MaybeUninit<T>> {
-    let value = mem::ManuallyDrop::new(value);
-    let ptr = &value as *const _ as *const Vec<MaybeUninit<T>>;
-    unsafe { ptr.read() }
+pub fn vec_to_uninit<T>(mut value: Vec<T>) -> Vec<MaybeUninit<T>> {
+    let (ptr, len, cap) = (value.as_mut_ptr() as *mut MaybeUninit<T>, value.len(), value.capacity());
+    mem::forget(value);
+    unsafe { Vec::from_raw_parts(ptr, len, cap) }
 }
 
 #[cfg(feature = "alloc")]
 pub fn boxed_slice_to_uninit<T>(value: Box<[T]>) -> Box<[MaybeUninit<T>]> {
-    let value = mem::ManuallyDrop::new(value);
-    let ptr = &value as *const _ as *const Box<[MaybeUninit<T>]>;
-    unsafe { ptr.read() }
+    let ptr = Box::into_raw(value) as *mut [MaybeUninit<T>];
+    unsafe { Box::from_raw(ptr) }
 }