Macro pinned_init::try_init

macro_rules! try_init {
    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
        $($fields:tt)*
    }) => { ... };
    ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
        $($fields:tt)*
    }? $err:ty) => { ... };
    (
        @this($($this:ident)?),
        @typ($t:ident $(::<$($generics:ty),*>)?),
        @fields($($fields:tt)*),
        @error($err:ty),
    ) => { ... };
    (init_slot:
        @slot($slot:ident),
        @munch_fields( $(,)?),
    ) => { ... };
    (init_slot:
        @slot($slot:ident),
        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
    ) => { ... };
    (init_slot:
        @slot($slot:ident),
        // Direct value init.
        @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
    ) => { ... };
    (make_initializer:
        @slot($slot:ident),
        @type_name($t:ident),
        @munch_fields( $(,)?),
        @acc($($acc:tt)*),
    ) => { ... };
    (make_initializer:
        @slot($slot:ident),
        @type_name($t:ident),
        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
        @acc($($acc:tt)*),
    ) => { ... };
    (make_initializer:
        @slot($slot:ident),
        @type_name($t:ident),
        @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
        @acc($($acc:tt)*),
    ) => { ... };
    (forget_guards:
        @munch_fields($(,)?),
    ) => { ... };
    (forget_guards:
        @munch_fields($field:ident <- $val:expr, $($rest:tt)*),
    ) => { ... };
    (forget_guards:
        @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
    ) => { ... };
}

Construct an in-place fallible initializer for structs.

This macro defaults the error to AllocError. If you need Infallible, then use init!.

The syntax is identical to try_pin_init!. If you want to specify a custom error, append ? $type after the struct initializer. The safety caveats from try_pin_init! also apply:

• unsafe code must guarantee either full initialization or return an error and allow deallocation of the memory.
• the fields are initialized in the order given in the initializer.
• no references to fields are allowed to be created inside of the initializer.

Examples

use pinned_init::*;
struct BigBuf {
    big: Box<[u8; 1024 * 1024 * 1024]>,
    small: [u8; 1024 * 1024],
}

impl BigBuf {
    fn new() -> impl Init<Self, AllocError> {
        try_init!(Self {
            big: Box::init(zeroed())?,
            small: [0; 1024 * 1024],
        }? AllocError)
    }
}