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//! `munge` makes it easy and safe to destructure `MaybeUninit`s, `Cell`s,
//! `UnsafeCell`s, `ManuallyDrop`s and more.
//!
//! Just use the `munge!` macro to destructure opaque types the same way you'd
//! destructure a value. The `munge!` macro may be used to perform either borrow
//! destructuring (e.g. `let (a, b) = c` where `c` is a reference) or move
//! destructuring (e.g. `let (a, b) = c` where `c` is a value) depending on the
//! type.
//!
//! `munge` has no features and is always `#![no_std]`.
//!
//! ## Examples
//!
//! `munge` makes it easy to initialize `MaybeUninit`s:
//!
//! ```rust
//! use {
//! ::core::mem::MaybeUninit,
//! ::munge::munge,
//! };
//!
//! pub struct Example {
//! a: u32,
//! b: (char, f32),
//! }
//!
//! let mut mu = MaybeUninit::<Example>::uninit();
//!
//! munge!(let Example { a, b: (c, mut f) } = &mut mu);
//! assert_eq!(a.write(10), &10);
//! assert_eq!(c.write('x'), &'x');
//! assert_eq!(f.write(3.14), &3.14);
//! // Note that `mut` bindings can be reassigned like you'd expect:
//! let mut new_f = MaybeUninit::uninit();
//! f = &mut new_f;
//!
//! // SAFETY: `mu` is completely initialized.
//! let init = unsafe { mu.assume_init() };
//! assert_eq!(init.a, 10);
//! assert_eq!(init.b.0, 'x');
//! assert_eq!(init.b.1, 3.14);
//! ```
//!
//! It can also be used to destructure `Cell`s:
//!
//! ```rust
//! use {
//! ::core::cell::Cell,
//! ::munge::munge,
//! };
//!
//! pub struct Example {
//! a: u32,
//! b: (char, f32),
//! }
//!
//! let value = Example {
//! a: 10,
//! b: ('x', 3.14),
//! };
//! let cell = Cell::<Example>::new(value);
//!
//! munge!(let Example { a, b: (c, f) } = &cell);
//! assert_eq!(a.get(), 10);
//! a.set(42);
//! assert_eq!(c.get(), 'x');
//! c.set('!');
//! assert_eq!(f.get(), 3.14);
//! f.set(1.41);
//!
//! let value = cell.into_inner();
//! assert_eq!(value.a, 42);
//! assert_eq!(value.b.0, '!');
//! assert_eq!(value.b.1, 1.41);
//! ```
//!
//! You can even extend `munge` to work with your own types by implementing its
//! [`Destructure`] and [`Restructure`] traits:
//!
//! ```rust
//! use munge::{Destructure, Restructure, Move, munge};
//!
//! pub struct Invariant<T>(T);
//!
//! impl<T> Invariant<T> {
//! /// # Safety
//! ///
//! /// `value` must uphold my custom invariant.
//! pub unsafe fn new_unchecked(value: T) -> Self {
//! Self(value)
//! }
//!
//! pub fn unwrap(self) -> T {
//! self.0
//! }
//! }
//!
//! // SAFETY:
//! // - `Invariant<T>` is destructured by move, so its `Destructuring` type is
//! // `Move`.
//! // - `underlying` returns a pointer to its inner type, so it is guaranteed
//! // to be non-null, properly aligned, and valid for reads.
//! unsafe impl<T> Destructure for Invariant<T> {
//! type Underlying = T;
//! type Destructuring = Move;
//!
//! fn underlying(&mut self) -> *mut Self::Underlying {
//! &mut self.0 as *mut Self::Underlying
//! }
//! }
//!
//! // SAFETY: `restructure` returns an `Invariant<U>` that takes ownership of
//! // the restructured field because `Invariant<T>` is destructured by move.
//! unsafe impl<T, U> Restructure<U> for Invariant<T> {
//! type Restructured = Invariant<U>;
//!
//! unsafe fn restructure(&self, ptr: *mut U) -> Self::Restructured {
//! // SAFETY: The caller has guaranteed that `ptr` is a pointer to a
//! // subfield of some `T`, so it must be properly aligned, valid for
//! // reads, and initialized. We may move the fields because the
//! // destructuring type for `Invariant<T>` is `Move`.
//! let value = unsafe { ptr.read() };
//! Invariant(value)
//! }
//! }
//!
//! // SAFETY: `(1, 2, 3)` upholds my custom invariant.
//! let value = unsafe { Invariant::new_unchecked((1, 2, 3)) };
//! munge!(let (one, two, three) = value);
//! assert_eq!(one.unwrap(), 1);
//! assert_eq!(two.unwrap(), 2);
//! assert_eq!(three.unwrap(), 3);
//! ```
#![no_std]
#![deny(
missing_docs,
unsafe_op_in_unsafe_fn,
clippy::missing_safety_doc,
clippy::undocumented_unsafe_blocks,
rustdoc::broken_intra_doc_links,
rustdoc::missing_crate_level_docs
)]
#[doc(hidden)]
pub mod __macro;
mod impls;
mod internal;
#[doc(hidden)]
pub use ::munge_macro::munge_with_path;
/// Projects a type to its fields using destructuring.
///
/// # Example
///
/// ```
/// # use { ::core::mem::MaybeUninit, ::munge::munge };
/// pub struct Example {
/// a: u32,
/// b: (char, f32),
/// }
///
/// let mut mu = MaybeUninit::<Example>::uninit();
///
/// munge!(let Example { a, b: (c, mut f) } = &mut mu);
/// assert_eq!(a.write(10), &10);
/// assert_eq!(c.write('x'), &'x');
/// assert_eq!(f.write(3.14), &3.14);
/// // Note that `mut` bindings can be reassigned like you'd expect:
/// let mut new_f = MaybeUninit::uninit();
/// f = &mut new_f;
///
/// // SAFETY: `mu` is completely initialized.
/// let init = unsafe { mu.assume_init() };
/// assert_eq!(init.a, 10);
/// assert_eq!(init.b.0, 'x');
/// assert_eq!(init.b.1, 3.14);
/// ```
#[macro_export]
macro_rules! munge {
($($t:tt)*) => { $crate::munge_with_path!($crate => $($t)*) }
}
/// A type that can be destructured into its constituent parts.
///
/// See the [crate docs](index.html#examples) for an example of implementing
/// `Destructure` and `Restructure`.
///
/// # Safety
///
/// - [`Destructuring`](Destructure::Destructuring) must reflect the type of
/// destructuring allowed for the type:
/// - [`Borrow`] if the type is restructured by creating disjoint borrows of
/// the fields of `Underlying`.
/// - [`Move`] if the type may be restructured by moving the fields out of
/// the destructured `Underlying`.
/// - [`underlying`](Destructure::underlying) must return a pointer that is
/// non-null, properly aligned, and valid for reads.
pub unsafe trait Destructure: Sized {
/// The underlying type that is destructured.
type Underlying: ?Sized;
/// The type of destructuring to perform.
type Destructuring: internal::Destructuring;
/// Returns a mutable pointer to the underlying type.
fn underlying(&mut self) -> *mut Self::Underlying;
}
/// A type that can be "restructured" as a field of some containing type.
///
/// See the [crate docs](index.html#examples) for an example of implementing
/// `Destructure` and `Restructure`.
///
/// # Safety
///
/// [`restructure`](Restructure::restructure) must return a valid
/// [`Restructured`](Restructure::Restructured) that upholds the invariants for
/// its [`Destructuring`](Destructure::Destructuring):
/// - If the type is destructured [by borrow](Borrow), then the `Restructured`
/// value must behave as a disjoint borrow of a field of the underlying type.
/// - If the type is destructured [by move](Move), then the `Restructured` value
/// must move the fields out of the underlying type.
pub unsafe trait Restructure<T: ?Sized>: Destructure {
/// The restructured version of this type.
type Restructured;
/// Restructures a pointer to this type into the target type.
///
/// # Safety
///
/// `ptr` must be a properly aligned pointer to a subfield of the pointer
/// [`underlying`](Destructure::underlying) `self`.
unsafe fn restructure(&self, ptr: *mut T) -> Self::Restructured;
}
/// Destructuring by borrow, e.g. `let (a, b) = c` where `c` is a reference.
///
/// Borrow destructuring leaves the original value intact, only borrowing from
/// the destructured value. Borrow destructuring may use rest patterns (`..`)
/// because the original value is not moved and so it is safe to restructure
/// only some of the fields of the destructured value.
pub struct Borrow;
impl internal::Destructuring for Borrow {}
impl<T: Destructure> internal::DestructuringFor<T> for Borrow {
type Destructurer = internal::Borrow<T>;
}
/// Destructuring by move, e.g. `let (a, b) = c` where `c` is a value.
///
/// Move destructuring forgets the original value and moves each destructured
/// field during restructuring. Move destructuring may not use rest patterns
/// (`..`) because every field of the original value must be restructured, else
/// they will be forgotten.
pub struct Move;
impl internal::Destructuring for Move {}
impl<T: Destructure> internal::DestructuringFor<T> for Move {
type Destructurer = internal::Move<T>;
}
#[cfg(test)]
mod tests {
use ::core::mem::MaybeUninit;
#[test]
fn project_tuple() {
let mut mu = MaybeUninit::<(u32, char)>::uninit();
munge!(let (a, b) = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
munge!(let (a, b,) = &mut mu);
assert_eq!(a.write(2), &2);
assert_eq!(b.write('b'), &'b');
munge!(let (a, _) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let (_, b) = &mut mu);
assert_eq!(b.write('c'), &'c');
munge!(let (a, _,) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let (_, b,) = &mut mu);
assert_eq!(b.write('c'), &'c');
munge!(let (mut a, mut b) = &mut mu);
assert_eq!(a.write(4), &4);
assert_eq!(b.write('d'), &'d');
let mut new_a = MaybeUninit::uninit();
a = &mut new_a;
let mut new_b = MaybeUninit::uninit();
b = &mut new_b;
let _ = a;
let _ = b;
munge!(let (a, ..) = &mut mu);
assert_eq!(a.write(5), &5);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.0, 5);
assert_eq!(init.1, 'd');
}
#[test]
fn project_array() {
let mut mu = MaybeUninit::<[u32; 2]>::uninit();
munge!(let [a, b] = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write(1), &1);
munge!(let [a, b,] = &mut mu);
assert_eq!(a.write(2), &2);
assert_eq!(b.write(2), &2);
munge!(let [a, _] = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let [_, b] = &mut mu);
assert_eq!(b.write(3), &3);
munge!(let [a, _,] = &mut mu);
assert_eq!(a.write(4), &4);
munge!(let [_, b,] = &mut mu);
assert_eq!(b.write(4), &4);
munge!(let [mut a, mut b] = &mut mu);
assert_eq!(a.write(5), &5);
assert_eq!(b.write(5), &5);
let mut new_a = MaybeUninit::uninit();
a = &mut new_a;
let mut new_b = MaybeUninit::uninit();
b = &mut new_b;
let _ = a;
let _ = b;
munge!(let [a, ..] = &mut mu);
assert_eq!(a.write(6), &6);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init[0], 6);
assert_eq!(init[1], 5);
}
#[test]
fn project_struct() {
pub struct Example {
pub a: u32,
pub b: char,
}
let mut mu = MaybeUninit::<Example>::uninit();
munge!(let Example { a, b } = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
munge!(let Example { a, b, } = &mut mu);
assert_eq!(a.write(2), &2);
assert_eq!(b.write('b'), &'b');
munge!(let Example { a, b: x } = &mut mu);
assert_eq!(a.write(3), &3);
assert_eq!(x.write('c'), &'c');
munge!(let Example { a, b: x, } = &mut mu);
assert_eq!(a.write(4), &4);
assert_eq!(x.write('d'), &'d');
munge!(let Example { a: x, b } = &mut mu);
assert_eq!(x.write(3), &3);
assert_eq!(b.write('c'), &'c');
munge!(let Example { a: x, b, } = &mut mu);
assert_eq!(x.write(4), &4);
assert_eq!(b.write('d'), &'d');
munge!(let Example { a, b: _ } = &mut mu);
assert_eq!(a.write(5), &5);
munge!(let Example { a, b: _, } = &mut mu);
assert_eq!(a.write(6), &6);
munge!(let Example { mut a, mut b } = &mut mu);
assert_eq!(a.write(7), &7);
assert_eq!(b.write('e'), &'e');
let mut new_a = MaybeUninit::uninit();
a = &mut new_a;
let mut new_b = MaybeUninit::uninit();
b = &mut new_b;
let _ = a;
let _ = b;
munge!(let Example { a: mut x, b: mut y } = &mut mu);
assert_eq!(x.write(8), &8);
assert_eq!(y.write('f'), &'f');
let mut new_x = MaybeUninit::uninit();
x = &mut new_x;
let mut new_y = MaybeUninit::uninit();
y = &mut new_y;
let _ = x;
let _ = y;
munge!(let Example { b, .. } = &mut mu);
assert_eq!(b.write('g'), &'g');
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.a, 8);
assert_eq!(init.b, 'g');
}
#[test]
fn project_tuple_struct() {
struct Example(u32, char);
let mut mu = MaybeUninit::<Example>::uninit();
munge!(let Example(a, b) = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
munge!(let Example(a, b,) = &mut mu);
assert_eq!(a.write(2), &2);
assert_eq!(b.write('b'), &'b');
munge!(let Example(a, _) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let Example(_, b) = &mut mu);
assert_eq!(b.write('c'), &'c');
munge!(let Example(a, _,) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let Example(_, b,) = &mut mu);
assert_eq!(b.write('d'), &'d');
munge!(let Example(mut a, mut b) = &mut mu);
assert_eq!(a.write(4), &4);
assert_eq!(b.write('e'), &'e');
let mut new_a = MaybeUninit::uninit();
a = &mut new_a;
let mut new_b = MaybeUninit::uninit();
b = &mut new_b;
let _ = a;
let _ = b;
munge!(let Example(a, ..) = &mut mu);
assert_eq!(a.write(5), &5);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.0, 5);
assert_eq!(init.1, 'e');
}
#[test]
fn project_generic() {
struct Example<T>(u32, T);
let mut mu = MaybeUninit::<Example<char>>::uninit();
munge!(let Example(a, b) = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
munge!(let Example(a, b,) = &mut mu);
assert_eq!(a.write(2), &2);
assert_eq!(b.write('b'), &'b');
munge!(let Example(a, _) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let Example(_, b) = &mut mu);
assert_eq!(b.write('c'), &'c');
munge!(let Example(a, _,) = &mut mu);
assert_eq!(a.write(3), &3);
munge!(let Example(_, b,) = &mut mu);
assert_eq!(b.write('c'), &'c');
munge!(let Example(a, ..) = &mut mu);
assert_eq!(a.write(4), &4);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.0, 4);
assert_eq!(init.1, 'c');
let mut mu = MaybeUninit::<Example<Example<char>>>::uninit();
munge!(
let Example::<Example<char>>(a, Example::<char>(b, c)) = &mut mu;
);
assert_eq!(a.write(1), &1);
assert_eq!(b.write(2), &2);
assert_eq!(c.write('a'), &'a');
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.0, 1);
assert_eq!(init.1 .0, 2);
assert_eq!(init.1 .1, 'a');
}
#[test]
fn project_nested_struct() {
struct Inner {
a: u32,
b: char,
}
struct Outer {
inner: Inner,
c: i32,
}
let mut mu = MaybeUninit::<Outer>::uninit();
munge!(let Outer { inner: Inner { a, b }, c } = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
assert_eq!(c.write(2), &2);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.inner.a, 1);
assert_eq!(init.inner.b, 'a');
assert_eq!(init.c, 2);
}
#[test]
fn project_nested_tuple() {
let mut mu = MaybeUninit::<(u32, (char, u32))>::uninit();
munge!(let (a, (b, c)) = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
assert_eq!(c.write(2), &2);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init, (1, ('a', 2)));
}
#[test]
fn project_nested_array() {
let mut mu = MaybeUninit::<[[u32; 2]; 2]>::uninit();
munge!(let [a, [b, c]] = &mut mu);
assert_eq!(a.write([1, 2]), &[1, 2]);
assert_eq!(b.write(3), &3);
assert_eq!(c.write(4), &4);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init, [[1, 2], [3, 4]]);
}
#[test]
fn generics() {
struct Inner<T> {
a: u32,
b: T,
}
struct Outer<T> {
inner: Inner<T>,
c: i32,
}
let mut mu = MaybeUninit::<Outer<char>>::uninit();
munge!(let Outer { inner: Inner { a, b }, c } = &mut mu);
assert_eq!(a.write(1), &1);
assert_eq!(b.write('a'), &'a');
assert_eq!(c.write(2), &2);
// SAFETY: `mu` is completely initialized.
let init = unsafe { mu.assume_init() };
assert_eq!(init.inner.a, 1);
assert_eq!(init.inner.b, 'a');
assert_eq!(init.c, 2);
}
#[test]
fn cell() {
use ::core::cell::Cell;
pub struct Example {
a: u32,
b: (char, f32),
}
let value = Example {
a: 10,
b: ('x', core::f32::consts::PI),
};
let cell = Cell::<Example>::new(value);
munge!(let Example { a, b: (c, f) } = &cell);
assert_eq!(a.get(), 10);
a.set(42);
assert_eq!(c.get(), 'x');
c.set('!');
assert_eq!(f.get(), core::f32::consts::PI);
f.set(1.41);
let value = cell.into_inner();
assert_eq!(value.a, 42);
assert_eq!(value.b.0, '!');
assert_eq!(value.b.1, 1.41);
}
#[test]
fn maybe_uninit_value() {
let mu = MaybeUninit::<(u32, char)>::new((10_000, 'x'));
munge!(let (a, b) = mu);
assert_eq!(unsafe { a.assume_init() }, 10_000);
assert_eq!(unsafe { b.assume_init() }, 'x');
}
#[test]
fn cell_value() {
use ::core::cell::Cell;
let cell = Cell::<(u32, char)>::new((10_000, 'x'));
munge!(let (a, b) = cell);
assert_eq!(a.get(), 10_000);
assert_eq!(b.get(), 'x');
}
#[test]
fn unsafe_cell_value() {
use ::core::cell::UnsafeCell;
let uc = UnsafeCell::<(u32, char)>::new((10_000, 'x'));
munge!(let (mut a, mut b) = uc);
assert_eq!(*a.get_mut(), 10_000);
assert_eq!(*b.get_mut(), 'x');
}
#[test]
fn manually_drop_value() {
use ::core::mem::ManuallyDrop;
let md = ManuallyDrop::new((10_000, 'x'));
munge!(let (a, b) = md);
assert_eq!(*a, 10_000);
assert_eq!(*b, 'x');
}
#[test]
fn struct_borrow_partial_destructuring() {
use ::core::cell::Cell;
struct Example {
a: u32,
b: u32,
}
let mut value = Cell::new(Example { a: 0, b: 1 });
munge!(let Example { a, .. } = &mut value);
assert_eq!(a.get(), 0);
a.set(2);
assert_eq!(a.get(), 2);
munge!(let Example { a: c, b: _ } = &value);
assert_eq!(c.get(), 2);
c.set(3);
assert_eq!(c.get(), 3);
}
#[test]
fn tuple_borrow_partial_destructuring() {
use ::core::cell::Cell;
struct Example(u32, u32);
let mut value = Cell::new(Example(0, 1));
munge!(let Example(a, ..) = &mut value);
assert_eq!(a.get(), 0);
a.set(2);
assert_eq!(a.get(), 2);
munge!(let Example(c, _) = &value);
assert_eq!(c.get(), 2);
c.set(3);
assert_eq!(c.get(), 3);
}
}