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// devela::sys::mem::namespace
//
//! Defines the [`Mem`] namespace.
//
#[allow(unused_imports, reason = "unsafe feature-gated")]
use crate::_core::{
mem::{transmute_copy, zeroed},
slice::{from_raw_parts, from_raw_parts_mut},
};
use crate::{
_core::mem::{
align_of, align_of_val, discriminant, drop, forget, needs_drop, replace, size_of,
size_of_val, swap, take,
},
Discriminant,
};
#[doc = crate::TAG_NAMESPACE!()]
/// Memory-related operations.
///
/// See also: [`ExtMem`][crate::ExtMem], [`Ptr`][crate::Ptr], [`Slice`][crate::Slice].
pub struct Mem;
/// # Safe methods.
impl Mem {
/// Returns the minimum alignment of the type in bytes.
///
/// See `core::mem::`[`align_of`].
#[must_use]
pub const fn align_of<T>() -> usize {
align_of::<T>()
}
/// Returns the alignment of the pointed-to value in bytes.
///
/// See `core::mem::`[`align_of_val`].
#[must_use]
pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
align_of_val(val)
}
/// Bitwise-copies a value.
///
/// It is useful when you want to pass a function pointer to a combinator,
/// rather than defining a new closure.
///
/// # Example
/// ```
/// # use devela::Mem;
/// let result_from_ffi_fn: Result<(), &i32> = Err(&1);
/// let result_copied: Result<(), i32> = result_from_ffi_fn.map_err(Mem::copy);
/// ```
// WAIT: [core::mem::copy](https://github.com/rust-lang/rust/issues/98262)
#[must_use]
pub const fn copy<T: Copy>(x: &T) -> T {
*x
}
/// Returns a value uniquely identifying the enum variant in v.
#[must_use]
pub const fn discriminant<T>(v: &T) -> Discriminant<T> {
discriminant(v)
}
/// Disposes of a value.
///
/// See `core::mem::`[`drop`].
pub fn drop<T>(_x: T) {
drop(_x);
}
/// Takes ownership and “forgets” about `t` *without running its destructor*.
///
/// See `core::mem::`[`forget`].
pub fn forget<T>(t: T) {
forget(t);
}
/// Returns true if dropping values of type T matters.
///
/// See `core::mem::`[`needs_drop`].
#[must_use]
pub const fn needs_drop<T: ?Sized>() -> bool {
needs_drop::<T>()
}
/// Moves `src` into `dest`, returning the previous `dest` value.
///
/// See `core::mem::`[`replace`].
#[must_use]
pub const fn replace<T>(dest: &mut T, src: T) -> T {
replace::<T>(dest, src)
}
/// Returns the size of a type in bytes.
///
/// See `core::mem::`[`size_of`].
#[must_use]
pub const fn size_of<T>() -> usize {
size_of::<T>()
}
/// Returns the size of the pointed-to value in bytes.
/// See `core::mem::`[`size_of_val`].
#[must_use]
pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
size_of_val(val)
}
/// Swaps the values at two locations, without deinitializing either one.
///
/// See `core::mem::`[`swap`].
pub const fn swap<T>(x: &mut T, y: &mut T) {
swap::<T>(x, y);
}
/// Replaces `dest` with `T::default()`, returning the previous `dest` value.
///
/// See `core::mem::`[`take`].
#[must_use]
pub fn take<T: Default>(dest: &mut T) -> T {
take::<T>(dest)
}
}
/// # Extra methods
impl Mem {
/// Returns the rounded up size in bytes from a size in bits.
///
/// This is equivalent to `(bit_size + 7) / 8` but handles potential overflow.
#[must_use]
pub const fn bytes_from_bits(bit_size: usize) -> usize {
if let Some(t) = bit_size.checked_add(8 - 1) {
t / 8
} else {
Self::bytes_from_bits_cold()
}
}
#[cold] #[rustfmt::skip]
const fn bytes_from_bits_cold() -> usize { usize::MAX / 8 }
}
/// # Unsafe methods
///
/// ## Features
/// They depend on enabling any `unsafe*` feature, and not enabling `safe_mem`.
#[cfg_attr(nightly_doc, doc(cfg(unsafe··)))]
#[cfg(all(not(feature = "safe_mem"), unsafe··))]
impl Mem {
// NOTE: can't compile, errors with: error[E0512]:
// cannot transmute between types of different sizes, or dependently-sized types
//
// /// Reinterprets the bits of a value of one type as another type.
// ///
// /// See `core::mem::`[`transmute`].
// pub const unsafe fn transmute<Src: Sized, Dst: Sized>(_src: Src) -> Dst {
// unsafe { transmute::<Src, Dst>(_src) }
// }
/// Reads `src` as having type `&Dst` without moving the contained value.
///
/// # Safety
/// See `core::mem::`[`transmute_copy`].
#[must_use]
pub const unsafe fn transmute_copy<Src, Dst>(src: &Src) -> Dst {
// SAFETY: Caller must uphold the safety contract.
unsafe { transmute_copy::<Src, Dst>(src) }
}
/// Returns the value of type `T` represented by the all-zero byte-pattern.
///
/// # Safety
/// See `core::mem::`[`zeroed`].
#[must_use]
pub const unsafe fn zeroed<T>() -> T {
// SAFETY: Caller must uphold the safety contract.
unsafe { zeroed::<T>() }
}
}
/// # Unsafe methods gated by `unsafe_slice`
#[cfg(all(not(feature = "safe_data"), feature = "unsafe_slice"))]
#[cfg_attr(nightly_doc, doc(cfg(feature = "unsafe_slice")))]
impl Mem {
/// View any `T: Sync + Unpin + ?Sized` as `&[u8]`.
///
/// This is a safer interface to `core::slice::`[`from_raw_parts`].
/// # Example
/// ```
/// # use devela::Mem;
/// #[repr(C)]
/// struct Data(u32);
///
/// let data = Data(1234);
/// let bytes = Mem::as_bytes(&data);
///
/// if cfg!(target_endian = "little") {
/// assert!(bytes == &[210, 4, 0, 0]);
/// } else {
/// assert!(bytes == &[0, 0, 4, 210]);
/// }
/// ```
#[doc = crate::doc_!(vendor: "rawbytes")]
#[must_use]
pub fn as_bytes<'t, T: Sync + Unpin + ?Sized + 't>(v: &T) -> &'t [u8] {
// SAFETY: `v` is valid; u8 has alignment 1, size_of_val(v) gives the exact byte length.
unsafe { from_raw_parts(v as *const _ as *const u8, size_of_val(v)) }
}
/// View any `T: Sync + Unpin + ?Sized` as `&mut [u8]`.
///
/// This is a safer interface to `core::slice::`[`from_raw_parts_mut`].
/// # Examples
/// ```
/// # use devela::Mem;
/// #[repr(C)]
/// struct Data(u32);
///
/// let mut data = Data(1234);
/// let bytes = Mem::as_bytes_mut(&mut data);
///
/// if cfg!(target_endian = "little") {
/// bytes[1] = 0;
/// assert!(bytes == &[210, 0, 0, 0] && data.0 == 210);
/// } else {
/// bytes[1] = 0;
/// assert!(bytes == &[0, 0, 0, 210] && data.0 == 210);
/// }
/// ```
#[doc = crate::doc_!(vendor: "rawbytes")]
#[must_use]
pub fn as_bytes_mut<'t, T: Sync + Unpin + ?Sized + 't>(v: &mut T) -> &'t mut [u8] {
// SAFETY: `v` is a valid, exclusive reference;
// u8’s alignment is 1, and size_of_val(v) bounds the mutable slice.
unsafe { from_raw_parts_mut(v as *mut _ as *mut u8, size_of_val(v)) }
}
/// View any `T: Sync + Unpin + Sized` as `&[u8]` *compile-time* friendly.
///
/// This is a safer interface to `core::slice::`[`from_raw_parts`], for `Sized` types.
/// # Examples
/// ```
/// # use devela::Mem;
/// const DATA: u32 = 1234;
/// const BYTES: &[u8] = Mem::as_bytes_sized(&DATA);
///
/// if cfg!(target_endian = "little") {
/// assert_eq!(BYTES, &[210, 4, 0, 0]);
/// } else {
/// assert_eq!(BYTES, &[0, 0, 4, 210]);
/// }
/// ```
#[must_use]
pub const fn as_bytes_sized<T: Sync + Unpin>(v: &T) -> &[u8] {
// SAFETY: `v` is valid; casting to *const u8 is safe (u8 has alignment 1)
// and size_of::<T>() exactly covers the object.
unsafe { from_raw_parts(v as *const T as *const u8, size_of::<T>()) }
}
}