Release 0.2.0

Author: djkoloski

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "munge"
-version = "0.1.1"
+version = "0.2.0"
 authors = ["David Koloski <[email protected]>"]
 edition = "2021"
 description = "Macro for easily initializing `MaybeUninit`s"

README.md

@@ -1,13 +1,14 @@
 # `munge`
 
-`munge` makes it easy to initialize `MaybeUninit`s.
+`munge` makes it easy and safe to destructure raw pointers, `MaybeUninit`s, `Cell`s, and `Pin`s.
 
-Just use the `munge!` macro to destructure `MaybeUninit`s the same way you'd destructure a value.
-Initialize all the fields, then call `assume_init` to unwrap it.
+Just use the `munge!` macro to destructure opaque types the same way you'd destructure a value.
 
 `munge` has no features and is always `#![no_std]`.
 
-## Example
+## Examples
+
+`munge` makes it easy to initialize `MaybeUninit`s:
 
 ```rust
 use {
@@ -22,7 +23,7 @@ pub struct Example {
 
 let mut mu = MaybeUninit::<Example>::uninit();
 
-munge!(let Example { a, b: (c, mut f) } = mu);
+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);
@@ -34,3 +35,74 @@ 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);
+```
+
+And `Pin`s as long as all fields are structurally pinned:
+
+```rust
+use {
+    ::core::{marker::PhantomPinned, pin::Pin},
+    ::munge::{munge, StructuralPinning},
+};
+
+struct Example {
+    pub a: u32,
+    pub b: char,
+    pub _phantom: PhantomPinned,
+}
+
+// SAFETY: `Example` obeys structural pinning.
+unsafe impl StructuralPinning for Example {}
+
+let mut value = Example {
+    a: 0,
+    b: ' ',
+    _phantom: PhantomPinned,
+};
+// SAFETY: `value` will not be moved before being dropped.
+let mut pin = unsafe { Pin::new_unchecked(&mut value) };
+
+munge!(let Example { a, b, .. } = pin.as_mut());
+*a.get_mut() = 1;
+*b.get_mut() = 'a';
+
+assert_eq!(pin.as_mut().into_ref().a, 1);
+assert_eq!(pin.as_mut().into_ref().b, 'a');
+assert_eq!(value.a, 1);
+assert_eq!(value.b, 'a');
+```
+
+You can even extend `munge` to work with your own types by implementing its `Destructure` and
+`Restructure` traits.

crates-io.md

@@ -1,11 +1,12 @@
-`munge` makes it easy to initialize `MaybeUninit`s.
+`munge` makes it easy and safe to destructure raw pointers, `MaybeUninit`s, `Cell`s, and `Pin`s.
 
-Just use the `munge!` macro to destructure `MaybeUninit`s the same way you'd destructure a value.
-Initialize all the fields, then call `assume_init` to unwrap it.
+Just use the `munge!` macro to destructure opaque types the same way you'd destructure a value.
 
 `munge` has no features and is always `#![no_std]`.
 
-## Example
+## Examples
+
+`munge` makes it easy to initialize `MaybeUninit`s:
 
 ```rust
 use {
@@ -20,7 +21,7 @@ pub struct Example {
 
 let mut mu = MaybeUninit::<Example>::uninit();
 
-munge!(let Example { a, b: (c, mut f) } = mu);
+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);
@@ -32,3 +33,74 @@ 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);
+```
+
+And `Pin`s as long as all fields are structurally pinned:
+
+```rust
+use {
+    ::core::{marker::PhantomPinned, pin::Pin},
+    ::munge::{munge, StructuralPinning},
+};
+
+struct Example {
+    pub a: u32,
+    pub b: char,
+    pub _phantom: PhantomPinned,
+}
+
+// SAFETY: `Example` obeys structural pinning.
+unsafe impl StructuralPinning for Example {}
+
+let mut value = Example {
+    a: 0,
+    b: ' ',
+    _phantom: PhantomPinned,
+};
+// SAFETY: `value` will not be moved before being dropped.
+let mut pin = unsafe { Pin::new_unchecked(&mut value) };
+
+munge!(let Example { a, b, .. } = pin.as_mut());
+*a.get_mut() = 1;
+*b.get_mut() = 'a';
+
+assert_eq!(pin.as_mut().into_ref().a, 1);
+assert_eq!(pin.as_mut().into_ref().b, 'a');
+assert_eq!(value.a, 1);
+assert_eq!(value.b, 'a');
+```
+
+You can even extend `munge` to work with your own types by implementing its `Destructure` and
+`Restructure` traits.

src/impls.rs

@@ -0,0 +1,164 @@
+use {
+    ::core::{cell::{Cell, UnsafeCell}, mem::MaybeUninit, pin::Pin},
+    crate::{Destructure, Restructure, StructuralPinning},
+};
+
+// *const T
+
+impl<T: ?Sized> Destructure for *const T {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        *self as *mut T
+    }
+}
+
+unsafe impl<T: ?Sized, U: ?Sized> Restructure<&*const T> for U {
+    type Restructured = *const Self;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        ptr as *const Self
+    }
+}
+
+// *mut T
+
+impl<T: ?Sized> Destructure for *mut T {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        *self
+    }
+}
+
+unsafe impl<T: ?Sized, U: ?Sized> Restructure<&*mut T> for U {
+    type Restructured = *mut Self;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        ptr
+    }
+}
+
+// &MaybeUninit
+
+impl<'a, T> Destructure for &'a MaybeUninit<T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        self.as_ptr() as *mut Self::Underlying
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T, U: 'b> Restructure<&'b &'a MaybeUninit<T>> for U {
+    type Restructured = &'b MaybeUninit<U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b &'a MaybeUninit<T>`, so it's safe to dereference for the `'b` lifetime.
+        unsafe { &*ptr.cast() }
+    }
+}
+
+// &mut MaybeUninit
+
+impl<'a, T> Destructure for &'a mut MaybeUninit<T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        MaybeUninit::as_mut_ptr(self)
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T, U: 'b> Restructure<&'b &'a mut MaybeUninit<T>> for U {
+    type Restructured = &'b mut MaybeUninit<U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b &'a mut MaybeUninit<T>`, so it's safe to mutably dereference for the `'b` lifetime.
+        unsafe { &mut *ptr.cast() }
+    }
+}
+
+// &Cell<T>
+
+impl<'a, T> Destructure for &'a Cell<T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        self.as_ptr()
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T, U: 'b> Restructure<&'b &'a Cell<T>> for U {
+    type Restructured = &'b Cell<U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b &'a Cell<T>`, so it's safe to dereference for the `'b` lifetime.
+        unsafe { &*ptr.cast() }
+    }
+}
+
+// &UnsafeCell<T>
+
+impl<'a, T> Destructure for &'a UnsafeCell<T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        self.get()
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T, U: 'b> Restructure<&'b &'a UnsafeCell<T>> for U {
+    type Restructured = &'b UnsafeCell<U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b &'a UnsafeCell<T>`, so it's safe to dereference for the `'b` lifetime.
+        unsafe { &*ptr.cast() }
+    }
+}
+
+// Pin<&T> where T: StructuralPinning
+
+impl<'a, T: StructuralPinning> Destructure for Pin<&'a T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        // SAFETY: The value pointed to by `self` will continue to be treated as pinned.
+        unsafe { Pin::into_inner_unchecked(self.as_ref()) as *const T as *mut T }
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T: StructuralPinning, U: 'b> Restructure<&'b Pin<&'a T>> for U {
+    type Restructured = Pin<&'b U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b Pin<&'a T>`, and `T` has structural pinning, so it's safe to derefence as pinned for
+        // the `'b` lifetime.
+        unsafe { Pin::new_unchecked(&*ptr) }
+    }
+}
+
+// Pin<&mut T> where T: StructuralPinning
+
+impl<'a, T: StructuralPinning> Destructure for Pin<&'a mut T> {
+    type Underlying = T;
+
+    fn as_mut_ptr(&mut self) -> *mut Self::Underlying {
+        // SAFETY: The value pointed to by `self` will continue to be treated as pinned.
+        unsafe { Pin::into_inner_unchecked(self.as_mut()) as *mut T }
+    }
+}
+
+unsafe impl<'a: 'b, 'b, T: StructuralPinning, U: 'b> Restructure<&'b Pin<&'a mut T>> for U {
+    type Restructured = Pin<&'b mut U>;
+
+    unsafe fn restructure(ptr: *mut Self) -> Self::Restructured {
+        // SAFETY: The caller has guaranteed that `ptr` points to a subfield of some
+        // `&'b Pin<&'a mut T>`, and `T` has structural pinning, so it's safe to mutably derefence
+        // as pinned for the `'b` lifetime.
+        unsafe { Pin::new_unchecked(&mut *ptr) }
+    }
+}