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#![no_std]
//! `align_of` and `size_of` as a macro, to avoid turbofish notation

#[doc(hidden)]
pub extern crate core as __core;

#[macro_export]
/// Returns the [ABI]-required minimum alignment of a type.
///
/// Every reference to a value of the type `T` must be a multiple of this number.
///
/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
///
/// [ABI]: https://en.wikipedia.org/wiki/Application_binary_interface
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate mem_macros;
///
/// # fn main() {
/// assert_eq!(4, align_of!(i32));
/// # }
/// ```
macro_rules! align_of {
    ($t:ty) => {
        $crate::__core::mem::align_of::<$t>()
    };
}

/// Returns the size of a type in bytes.
///
/// More specifically, this is the offset in bytes between successive elements
/// in an array with that item type including alignment padding. Thus, for any
/// type `T` and length `n`, `[T; n]` has a size of `n * size_of!(T)`.
///
/// In general, the size of a type is not stable across compilations, but
/// specific types such as primitives are.
///
/// The following table gives the size for primitives.
///
/// Type | size_of!(Type)
/// ---- | ---------------
/// () | 0
/// bool | 1
/// u8 | 1
/// u16 | 2
/// u32 | 4
/// u64 | 8
/// i8 | 1
/// i16 | 2
/// i32 | 4
/// i64 | 8
/// f32 | 4
/// f64 | 8
/// char | 4
///
/// Furthermore, `usize` and `isize` have the same size.
///
/// The types `*const T`, `&T`, `Box<T>`, `Option<&T>`, and `Option<Box<T>>` all have
/// the same size. If `T` is Sized, all of those types have the same size as `usize`.
///
/// The mutability of a pointer does not change its size. As such, `&T` and `&mut T`
/// have the same size. Likewise for `*const T` and `*mut T`.
///
/// # Size of `#[repr(C)]` items
///
/// The `C` representation for items has a defined layout. With this layout,
/// the size of items is also stable as long as all fields have a stable size.
///
/// ## Size of Structs
///
/// For `structs`, the size is determined by the following algorithm.
///
/// For each field in the struct ordered by declaration order:
///
/// 1. Add the size of the field.
/// 2. Round up the current size to the nearest multiple of the next field's [alignment].
///
/// Finally, round the size of the struct to the nearest multiple of its [alignment].
///
/// Unlike `C`, zero sized structs are not rounded up to one byte in size.
///
/// ## Size of Enums
///
/// Enums that carry no data other than the descriminant have the same size as C enums
/// on the platform they are compiled for.
///
/// ## Size of Unions
///
/// The size of a union is the size of its largest field.
///
/// Unlike `C`, zero sized unions are not rounded up to one byte in size.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate mem_macros;
///
/// # fn main() {
/// // Some primitives
/// assert_eq!(4, size_of!(i32));
/// assert_eq!(8, size_of!(f64));
/// assert_eq!(0, size_of!(()));
///
/// // Some arrays
/// assert_eq!(8, size_of!([i32; 2]));
/// assert_eq!(12, size_of!([i32; 3]));
/// assert_eq!(0, size_of!([i32; 0]));
///
///
/// // Pointer size equality
/// assert_eq!(size_of!(&i32), size_of!(*const i32));
/// assert_eq!(size_of!(&i32), size_of!(Box<i32>));
/// assert_eq!(size_of!(&i32), size_of!(Option<&i32>));
/// assert_eq!(size_of!(Box<i32>), size_of!(Option<Box<i32>>));
/// # }
/// ```
///
/// Using `#[repr(C)]`.
///
/// ```
/// #[macro_use]
/// extern crate mem_macros;
///
/// # fn main() {
/// #[repr(C)]
/// struct FieldStruct {
///     first: u8,
///     second: u16,
///     third: u8
/// }
///
/// // The size of the first field is 1, so add 1 to the size. Size is 1.
/// // The alignment of the second field is 2, so add 1 to the size for padding. Size is 2.
/// // The size of the second field is 2, so add 2 to the size. Size is 4.
/// // The alignment of the third field is 1, so add 0 to the size for padding. Size is 4.
/// // The size of the third field is 1, so add 1 to the size. Size is 5.
/// // Finally, the alignment of the struct is 2, so add 1 to the size for padding. Size is 6.
/// assert_eq!(6, size_of!(FieldStruct));
///
/// #[repr(C)]
/// struct TupleStruct(u8, u16, u8);
///
/// // Tuple structs follow the same rules.
/// assert_eq!(6, size_of!(TupleStruct));
///
/// // Note that reordering the fields can lower the size. We can remove both padding bytes
/// // by putting `third` before `second`.
/// #[repr(C)]
/// struct FieldStructOptimized {
///     first: u8,
///     third: u8,
///     second: u16
/// }
///
/// assert_eq!(4, size_of!(FieldStructOptimized));
///
/// // Union size is the size of the largest field.
/// #[repr(C)]
/// union ExampleUnion {
///     smaller: u8,
///     larger: u16
/// }
///
/// assert_eq!(2, size_of!(ExampleUnion));
/// # }
/// ```
#[macro_export]
macro_rules! size_of {
    ($t:ty) => {
        $crate::__core::mem::size_of::<$t>()
    };
}