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#![no_std] #![allow(warnings)] //! Typic helps you transmute fearlessly. It worries about the subtleties of //! ***[soundness]*** and ***[safety]*** so you don't have to! //! //! Just import it and replace your `#[repr(...)]` attributes with `#[typic::repr(...)]`: //! ``` //! // Import it! //! use typic::{self, transmute::StableTransmuteInto, stability::StableABI}; //! //! // Update your attributes! //! #[typic::repr(C)] //! #[derive(StableABI)] //! pub struct Foo(pub u8, pub u16); //! //! // Transmute fearlessly! //! let _ : Foo = 64u32.transmute_into(); // Alchemy achieved! //! ``` //! ```compile_fail //! # use typic::{self, TransmuteInto}; //! # #[typic::repr(C)] //! # #[derive(StableABI)] //! # struct Foo(pub u8, pub u16); //! let _ : u32 = Foo(16, 12).transmute_into(); // Compile Error! //! ``` //! //! [soundness]: crate::transmute::unsafe_transmutation#when-is-a-transmutation-sound //! [safety]: crate::transmute::safe_transmutation #[doc(hidden)] pub mod docs { pub mod prelude { pub use crate::stability::StableABI; pub use crate::transmute::{unsafe_transmute, StableTransmuteInto}; use crate::typic; pub use core::mem; pub use core::num::NonZeroU8; #[typic::repr(C)] #[derive(Default, StableABI)] pub struct Padded(pub u8, pub u16, pub u8); #[typic::repr(C)] #[derive(Default, StableABI)] pub struct Packed(pub u16, pub u16, pub u16); #[typic::repr(C)] #[derive(Default, StableABI)] pub struct Constrained { wizz: i8, bang: u8, } impl Constrained { /// the sum of `wizz` and `bang` must be greater than or equal to zero. pub fn new(wizz: i8, bang: u8) -> Self { assert!((wizz as i16) / (bang as i16) >= 0); Constrained { wizz, bang } } pub fn something_dangerous(&self) { unsafe { // do something that's only safe if `wizz + bang >= 0` } } } #[typic::repr(C)] #[derive(Default, StableABI)] pub struct Unconstrained { pub wizz: u8, pub bang: i8, } } } #[doc(hidden)] #[deprecated(note = "TODO")] pub enum TODO {} #[doc(hidden)] pub mod private { pub mod bytelevel; pub mod highlevel; pub mod layout; pub mod num; pub mod stability; pub mod target; pub mod transmute; } #[doc(hidden)] pub use private::highlevel as internal; /// Use `#[typic::repr(...)]` instead of `#[repr(...)]` on your type definitions. #[doc(inline)] pub use typic_derive::repr; #[doc(inline)] pub use private::stability; pub mod transmute; mod typic { pub use super::*; } /// Details about the layout of types. /// /// [`SizeOf`]: crate::layout::SizeOf /// [`zerocopy`]: https://crates.io/crates/zerocopy /// [`AsBytes`]: https://docs.rs/zerocopy/0.2.*/zerocopy/trait.AsBytes.html /// [`FromBytes`]: https://docs.rs/zerocopy/0.2.*/zerocopy/trait.FromBytes.html /// [`Unaligned`]: https://docs.rs/zerocopy/0.2.*/zerocopy/trait.Unaligned.html /// /// Useful for building your own abstractions over Typic. For instance, we can /// use [`SizeOf`] to implement [`zerocopy`]'s [`FromBytes`], [`AsBytes`] and /// [`Unaligned`] marker traits: /// /// ``` /// use typic::{layout::{Layout, SizeOf}, transmute::TransmuteInto, transmute::TransmuteFrom}; /// use generic_array::{ArrayLength as Length, GenericArray as Array}; /// use typenum::U1; /// /// /// Indicates `Self` can be produced from an /// /// appropriately-sized array of arbitrarily /// /// initialized bytes. /// pub trait FromBytes {} /// /// impl<T> FromBytes for T /// where /// T: Layout, /// SizeOf<T>: Length<u8>, /// T: TransmuteFrom<Array<u8, SizeOf<T>>> /// {} /// /// /// Indicates `Self` can be converted into an /// /// appropriately-sized array of arbitrarily /// /// initialized bytes. /// pub trait AsBytes {} /// /// impl<T> AsBytes for T /// where /// T: Layout, /// SizeOf<T>: Length<u8>, /// T: TransmuteInto<Array<u8, SizeOf<T>>> /// {} /// /// /// Indicates `Self` has no alignment requirement. /// pub trait Unaligned {} /// /// impl<T> Unaligned for T /// where /// T: Layout<Align=U1>, /// {} /// ``` pub mod layout { use crate::internal::{Private, Public}; use crate::private::{layout, num}; use generic_array::ArrayLength; /// Type-level information about type representation. pub trait Layout: layout::Layout<Public> { /// The size of `Self`. /// /// ``` /// use typenum::*; /// use static_assertions::*; /// use typic::layout::Layout; /// /// assert_type_eq_all!(U4, <[u16; 2] as Layout>::Size); /// ``` type Size: num::Unsigned + ArrayLength<u8>; /// The minimum alignment of `Self`. /// /// ``` /// use typenum::*; /// use static_assertions::*; /// use typic::layout::Layout; /// /// assert_type_eq_all!(U2, <[u16; 2] as Layout>::Align); /// ``` type Align: num::Unsigned; } impl<T> Layout for T where T: layout::Layout<Public>, { type Size = <T as layout::Layout<Public>>::Size; type Align = <T as layout::Layout<Public>>::Align; } /// Get the size of `T` (if `T: Layout`). /// /// ``` /// use typenum::*; /// use static_assertions::*; /// use typic::layout::SizeOf; /// /// assert_type_eq_all!(U4, SizeOf<[u16; 2]>); /// ``` pub type SizeOf<T> = <T as Layout>::Size; /// Get the minimum alignment of `T` (if `T: Layout`). /// /// ``` /// use typenum::*; /// use static_assertions::*; /// use typic::layout::AlignOf; /// /// assert_type_eq_all!(U2, AlignOf<[u16; 2]>); /// ``` pub type AlignOf<T> = <T as Layout>::Align; } /// Examples demonstrating typic's ability to express common abstractions. pub mod extras { /// [Zerocopy](https://docs.rs/zerocopy)-style marker traits. pub mod zerocopy { use crate::layout::*; use crate::transmute::*; use typenum::U1; use generic_array::{ArrayLength as Length, GenericArray as Array}; /// Indicates `Self` can be produced from an /// appropriately-sized array of arbitrarily /// initialized bytes. pub unsafe trait FromBytes<O: TransmuteOptions = ()> {} unsafe impl<T, O: TransmuteOptions> FromBytes<O> for T where T: Layout + TransmuteFrom<Array<u8, SizeOf<T>>, O> {} /// Indicates `Self` can be converted into an /// appropriately-sized array of arbitrarily /// initialized bytes. pub unsafe trait AsBytes<O: TransmuteOptions = ()> {} unsafe impl<T, O: TransmuteOptions> AsBytes<O> for T where T: Layout + TransmuteInto<Array<u8, SizeOf<T>>, O> {} /// Indicates `Self` has no alignment requirement. pub trait Unaligned {} impl<T> Unaligned for T where T: Layout<Align=U1>, {} } /// [Bytemuck](https://docs.rs/bytemuck)-style casting functions. pub mod bytemuck { use crate::transmute::*; use core::mem::{align_of, size_of, size_of_val}; /// Try to convert a `&T` into `&U`. /// /// This produces `None` if the referent isn't appropriately /// aligned, as required by the destination type. /// /// Like [`bytemuck::try_cast_ref`], except that invariant /// that `T` and `U` have the same size is statically enforced. /// /// [`bytemuck::try_cast_ref`]: https://docs.rs/bytemuck/1.2.0/bytemuck/fn.try_cast_ref.html pub fn try_cast_ref<'t, 'u, T, U>(src: &'t T) -> Option<&'u U> where &'t T: UnsafeTransmuteInto<&'u U, neglect::Alignment>, { if align_of::<U>() > align_of::<T>() && (src as *const T as usize) % align_of::<U>() != 0 { None } else { // Sound, because we dynamically enforce the alignment // requirement, whose static check we chose to neglect. Some(unsafe { src.unsafe_transmute_into() }) } } use core::slice; use generic_array::{ArrayLength as Length, GenericArray as Array}; use crate::layout::*; /// Try to convert a `&T` into `&U`. /// /// This produces `None` if the referent isn't appropriately /// aligned, as required by the destination type. /// /// Like [`bytemuck::try_cast_slice`], except that invariant /// that `T` and `U` have the same size is statically enforced. /// /// If const generics were stable, the trait bound would /// be instead written as just: /// ```ignore /// &'t [T; size_of::<U>()]: /// TransmuteInto<&'u [U; size_of::<T>()]> /// ``` /// /// [`bytemuck::try_cast_slice`]: https://docs.rs/bytemuck/1.2.0/bytemuck/fn.try_cast_slice.html pub fn try_cast_slice<'t, 'u, T, U>(src: &'t [T]) -> Option<&'u [U]> where &'t Array<T, SizeOf<U>>: TransmuteInto<&'u Array<U, SizeOf<T>>>, T: Layout, U: Layout, SizeOf<T>: 'u + Length<U>, SizeOf<U>: 't + Length<T>, { if align_of::<U>() > align_of::<T>() && (src.as_ptr() as usize) % align_of::<U>() != 0 { None } else { let len = size_of_val(src).checked_div(size_of::<U>()).unwrap_or(0); Some(unsafe { slice::from_raw_parts(src.as_ptr() as *const U, len) }) } } } }