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101 lines
2.6 KiB
101 lines
2.6 KiB
/// A pinned projection of a struct field.
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///
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/// # Safety
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///
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/// To make using this macro safe, three things need to be ensured:
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/// - If the struct implements [`Drop`], the [`drop`] method is not allowed to
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/// move the value of the field.
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/// - If the struct wants to implement [`Unpin`], it has to do so conditionally:
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/// The struct can only implement [`Unpin`] if the field's type is [`Unpin`].
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/// - The struct must not be `#[repr(packed)]`.
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///
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/// # Example
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///
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/// ```rust
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/// use pin_utils::unsafe_pinned;
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/// use std::marker::Unpin;
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/// use std::pin::Pin;
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///
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/// struct Foo<T> {
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/// field: T,
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/// }
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///
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/// impl<T> Foo<T> {
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/// unsafe_pinned!(field: T);
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///
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/// fn baz(mut self: Pin<&mut Self>) {
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/// let _: Pin<&mut T> = self.field(); // Pinned reference to the field
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/// }
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/// }
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///
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/// impl<T: Unpin> Unpin for Foo<T> {} // Conditional Unpin impl
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/// ```
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///
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/// Note: borrowing the field multiple times requires using `.as_mut()` to
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/// avoid consuming the `Pin`.
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///
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/// [`Unpin`]: core::marker::Unpin
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/// [`drop`]: Drop::drop
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#[macro_export]
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macro_rules! unsafe_pinned {
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($f:tt: $t:ty) => (
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#[allow(unsafe_code)]
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fn $f<'__a>(
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self: $crate::core_reexport::pin::Pin<&'__a mut Self>
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) -> $crate::core_reexport::pin::Pin<&'__a mut $t> {
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unsafe {
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$crate::core_reexport::pin::Pin::map_unchecked_mut(
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self, |x| &mut x.$f
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)
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}
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}
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)
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}
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/// An unpinned projection of a struct field.
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///
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/// # Safety
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///
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/// This macro is unsafe because it creates a method that returns a normal
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/// non-pin reference to the struct field. It is up to the programmer to ensure
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/// that the contained value can be considered not pinned in the current
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/// context.
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///
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/// # Example
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///
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/// ```rust
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/// use pin_utils::unsafe_unpinned;
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/// use std::pin::Pin;
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///
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/// struct Bar;
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/// struct Foo {
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/// field: Bar,
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/// }
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///
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/// impl Foo {
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/// unsafe_unpinned!(field: Bar);
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///
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/// fn baz(mut self: Pin<&mut Self>) {
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/// let _: &mut Bar = self.field(); // Normal reference to the field
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/// }
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/// }
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/// ```
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///
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/// Note: borrowing the field multiple times requires using `.as_mut()` to
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/// avoid consuming the [`Pin`].
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///
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/// [`Pin`]: core::pin::Pin
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#[macro_export]
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macro_rules! unsafe_unpinned {
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($f:tt: $t:ty) => (
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#[allow(unsafe_code)]
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fn $f<'__a>(
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self: $crate::core_reexport::pin::Pin<&'__a mut Self>
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) -> &'__a mut $t {
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unsafe {
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&mut $crate::core_reexport::pin::Pin::get_unchecked_mut(self).$f
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}
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}
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)
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}
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