# Macro pin_utils::unsafe_pinned [−] [src]

    macro_rules! unsafe_pinned {
        ($f:tt: $t:ty) => { ... };
    }

A pinned projection of a struct field.

# Safety

To make using this macro safe, three things need to be ensured:

- If the struct implements `Drop`, the `drop` method is not allowed to move the value of the field.
- If the struct wants to implement `Unpin`, it has to do so conditionally: The struct can only implement `Unpin` if the field’s type is `Unpin`.
- The struct must not be `#[repr(packed)]`.

# Example

    use pin_utils::unsafe_pinned;
    use std::marker::Unpin;
    use std::pin::Pin;

    struct Foo<T> {
        field: T,
    }

    impl<T> Foo<T> {
        unsafe_pinned!(field: T);

        fn baz(mut self: Pin<&mut Self>) {
            let _: Pin<&mut T> = self.field(); // Pinned reference to the field
        }
    }

    impl<T: Unpin> Unpin for Foo<T> {} // Conditional Unpin impl

Note: borrowing the field multiple times requires using `.as_mut()` to avoid consuming the `Pin`.