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Feat: genericize ptr::from_raw_parts #5

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2a8024d
Feat: genericize ptr::from_raw_parts (https://github.com/rust-lang/ru…
stegaBOB Apr 14, 2025
ed7cec2
Fix doc tests
stegaBOB Apr 14, 2025
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6 changes: 3 additions & 3 deletions ptr_meta/example.md
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ assert_eq!(ptr_meta::metadata(slice), slice.len());

// Make your own wide pointers from data pointers and metadata
let bytes = [b'h', b'e', b'l', b'l', b'o'];
let ptr = ptr_meta::from_raw_parts::<str>(bytes.as_ptr().cast(), 5);
let ptr = ptr_meta::from_raw_parts::<str>(bytes.as_ptr(), 5);
println!("{} world!", unsafe { &*ptr }); // prints "hello world!"

// Derive Pointee on your own types
Expand All @@ -24,7 +24,7 @@ impl CoolStr {
}
}

let ptr = ptr_meta::from_raw_parts::<CoolStr>(bytes.as_ptr().cast(), 5);
let ptr = ptr_meta::from_raw_parts::<CoolStr>(bytes.as_ptr(), 5);
let cool = unsafe { &*ptr };
cool.print_cool(); // prints "😎 hello 😎"

Expand All @@ -43,7 +43,7 @@ impl Printable for i32 {
let i32_vtable = ptr_meta::metadata(&0i32 as &dyn Printable);
let one_hundred = 100i32;
let printable = ptr_meta::from_raw_parts::<dyn Printable>(
(&one_hundred as *const i32).cast(),
(&one_hundred as *const i32),
i32_vtable,
);
unsafe {
Expand Down
14 changes: 10 additions & 4 deletions ptr_meta/src/lib.rs
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Expand Up @@ -167,6 +167,12 @@ unsafe impl Pointee for std::ffi::OsStr {
type Metadata = usize;
}

/// Pointers to types implementing this trait alias are “thin”.
///
/// This includes statically-Sized types and extern types.
pub trait Thin: Pointee<Metadata = ()> {}
impl<T: Pointee<Metadata = ()>> Thin for T {}

/// Returns the metadata of the given pointer.
///
/// `*mut T`, `&T`, and `&mut T` can all be passed directly to this function as
Expand Down Expand Up @@ -227,7 +233,7 @@ pub const fn to_raw_parts_mut<T: Pointee + ?Sized>(
/// [`slice::from_raw_parts`]: core::slice::from_raw_parts
#[inline]
pub const fn from_raw_parts<T: Pointee + ?Sized>(
data_address: *const (),
data_address: *const impl Thin,
metadata: <T as Pointee>::Metadata,
) -> *const T {
// SAFETY: Accessing the value from the `PtrRepr` union is safe since
Expand All @@ -236,7 +242,7 @@ pub const fn from_raw_parts<T: Pointee + ?Sized>(
unsafe {
PtrRepr {
components: PtrComponents {
data_address,
data_address: data_address.cast(),
metadata,
},
}
Expand All @@ -249,7 +255,7 @@ pub const fn from_raw_parts<T: Pointee + ?Sized>(
/// See [`from_raw_parts`] for more details.
#[inline]
pub const fn from_raw_parts_mut<T: Pointee + ?Sized>(
data_address: *mut (),
data_address: *mut impl Thin,
metadata: <T as Pointee>::Metadata,
) -> *mut T {
// SAFETY: Accessing the value from the `PtrRepr` union is safe since
Expand All @@ -258,7 +264,7 @@ pub const fn from_raw_parts_mut<T: Pointee + ?Sized>(
unsafe {
PtrRepr {
components: PtrComponents {
data_address,
data_address: data_address.cast(),
metadata,
},
}
Expand Down