array.rs

//! Implementations of things like `Eq` for fixed-length arrays
//! up to a certain length. Eventually we should able to generalize
//! to all lengths.
//!
//! *[See also the array primitive type](../../std/primitive.array.html).*

#![unstable(feature = "fixed_size_array",
            reason = "traits and impls are better expressed through generic \
                      integer constants",
            issue = "27778")]

use crate::borrow::{Borrow, BorrowMut};
use crate::cmp::Ordering;
use crate::convert::TryFrom;
use crate::fmt;
use crate::hash::{Hash, self};
use crate::marker::Unsize;
use crate::slice::{Iter, IterMut};

/// Utility trait implemented only on arrays of fixed size
///
/// This trait can be used to implement other traits on fixed-size arrays
/// without causing much metadata bloat.
///
/// The trait is marked unsafe in order to restrict implementors to fixed-size
/// arrays. User of this trait can assume that implementors have the exact
/// layout in memory of a fixed size array (for example, for unsafe
/// initialization).
///
/// Note that the traits AsRef and AsMut provide similar methods for types that
/// may not be fixed-size arrays. Implementors should prefer those traits
/// instead.
pub unsafe trait FixedSizeArray<T> {
    /// Converts the array to immutable slice
    fn as_slice(&self) -> &[T];
    /// Converts the array to mutable slice
    fn as_mut_slice(&mut self) -> &mut [T];
}

unsafe impl<T, A: Unsize<[T]>> FixedSizeArray<T> for A {
    #[inline]
    fn as_slice(&self) -> &[T] {
        self
    }
    #[inline]
    fn as_mut_slice(&mut self) -> &mut [T] {
        self
    }
}

/// The error type returned when a conversion from a slice to an array fails.
#[stable(feature = "try_from", since = "1.34.0")]
#[derive(Debug, Copy, Clone)]
pub struct TryFromSliceError(());

impl fmt::Display for TryFromSliceError {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(self.__description(), f)
    }
}

impl TryFromSliceError {
    #[unstable(feature = "array_error_internals",
           reason = "available through Error trait and this method should not \
                     be exposed publicly",
           issue = "0")]
    #[inline]
    #[doc(hidden)]
    pub fn __description(&self) -> &str {
        "could not convert slice to array"
    }
}

macro_rules! __impl_slice_eq1 {
    ($Lhs: ty, $Rhs: ty) => {
        __impl_slice_eq1! { $Lhs, $Rhs, Sized }
    };
    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
            #[inline]
            fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
            #[inline]
            fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
        }
    }
}

macro_rules! __impl_slice_eq2 {
    ($Lhs: ty, $Rhs: ty) => {
        __impl_slice_eq2! { $Lhs, $Rhs, Sized }
    };
    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
        __impl_slice_eq1!($Lhs, $Rhs, $Bound);

        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a, 'b, A: $Bound, B> PartialEq<$Lhs> for $Rhs where B: PartialEq<A> {
            #[inline]
            fn eq(&self, other: &$Lhs) -> bool { self[..] == other[..] }
            #[inline]
            fn ne(&self, other: &$Lhs) -> bool { self[..] != other[..] }
        }
    }
}

// macro for implementing n-element array functions and operations
macro_rules! array_impls {
    ($($N:expr)+) => {
        $(
            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T> AsRef<[T]> for [T; $N] {
                #[inline]
                fn as_ref(&self) -> &[T] {
                    &self[..]
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T> AsMut<[T]> for [T; $N] {
                #[inline]
                fn as_mut(&mut self) -> &mut [T] {
                    &mut self[..]
                }
            }

            #[stable(feature = "array_borrow", since = "1.4.0")]
            impl<T> Borrow<[T]> for [T; $N] {
                fn borrow(&self) -> &[T] {
                    self
                }
            }

            #[stable(feature = "array_borrow", since = "1.4.0")]
            impl<T> BorrowMut<[T]> for [T; $N] {
                fn borrow_mut(&mut self) -> &mut [T] {
                    self
                }
            }

            #[stable(feature = "try_from", since = "1.34.0")]
            impl<T> TryFrom<&[T]> for [T; $N] where T: Copy {
                type Error = TryFromSliceError;

                fn try_from(slice: &[T]) -> Result<[T; $N], TryFromSliceError> {
                    <&Self>::try_from(slice).map(|r| *r)
                }
            }

            #[stable(feature = "try_from", since = "1.34.0")]
            impl<'a, T> TryFrom<&'a [T]> for &'a [T; $N] {
                type Error = TryFromSliceError;

                fn try_from(slice: &[T]) -> Result<&[T; $N], TryFromSliceError> {
                    if slice.len() == $N {
                        let ptr = slice.as_ptr() as *const [T; $N];
                        unsafe { Ok(&*ptr) }
                    } else {
                        Err(TryFromSliceError(()))
                    }
                }
            }

            #[stable(feature = "try_from", since = "1.34.0")]
            impl<'a, T> TryFrom<&'a mut [T]> for &'a mut [T; $N] {
                type Error = TryFromSliceError;

                fn try_from(slice: &mut [T]) -> Result<&mut [T; $N], TryFromSliceError> {
                    if slice.len() == $N {
                        let ptr = slice.as_mut_ptr() as *mut [T; $N];
                        unsafe { Ok(&mut *ptr) }
                    } else {
                        Err(TryFromSliceError(()))
                    }
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T: Hash> Hash for [T; $N] {
                fn hash<H: hash::Hasher>(&self, state: &mut H) {
                    Hash::hash(&self[..], state)
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T: fmt::Debug> fmt::Debug for [T; $N] {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    fmt::Debug::fmt(&&self[..], f)
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<'a, T> IntoIterator for &'a [T; $N] {
                type Item = &'a T;
                type IntoIter = Iter<'a, T>;

                fn into_iter(self) -> Iter<'a, T> {
                    self.iter()
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<'a, T> IntoIterator for &'a mut [T; $N] {
                type Item = &'a mut T;
                type IntoIter = IterMut<'a, T>;

                fn into_iter(self) -> IterMut<'a, T> {
                    self.iter_mut()
                }
            }

            // NOTE: some less important impls are omitted to reduce code bloat
            __impl_slice_eq1! { [A; $N], [B; $N] }
            __impl_slice_eq2! { [A; $N], [B] }
            __impl_slice_eq2! { [A; $N], &'b [B] }
            __impl_slice_eq2! { [A; $N], &'b mut [B] }
            // __impl_slice_eq2! { [A; $N], &'b [B; $N] }
            // __impl_slice_eq2! { [A; $N], &'b mut [B; $N] }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T:Eq> Eq for [T; $N] { }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T:PartialOrd> PartialOrd for [T; $N] {
                #[inline]
                fn partial_cmp(&self, other: &[T; $N]) -> Option<Ordering> {
                    PartialOrd::partial_cmp(&&self[..], &&other[..])
                }
                #[inline]
                fn lt(&self, other: &[T; $N]) -> bool {
                    PartialOrd::lt(&&self[..], &&other[..])
                }
                #[inline]
                fn le(&self, other: &[T; $N]) -> bool {
                    PartialOrd::le(&&self[..], &&other[..])
                }
                #[inline]
                fn ge(&self, other: &[T; $N]) -> bool {
                    PartialOrd::ge(&&self[..], &&other[..])
                }
                #[inline]
                fn gt(&self, other: &[T; $N]) -> bool {
                    PartialOrd::gt(&&self[..], &&other[..])
                }
            }

            #[stable(feature = "rust1", since = "1.0.0")]
            impl<T:Ord> Ord for [T; $N] {
                #[inline]
                fn cmp(&self, other: &[T; $N]) -> Ordering {
                    Ord::cmp(&&self[..], &&other[..])
                }
            }
        )+
    }
}

array_impls! {
     0  1  2  3  4  5  6  7  8  9
    10 11 12 13 14 15 16 17 18 19
    20 21 22 23 24 25 26 27 28 29
    30 31 32
}

// The Default impls cannot be generated using the array_impls! macro because
// they require array literals.

macro_rules! array_impl_default {
    {$n:expr, $t:ident $($ts:ident)*} => {
        #[stable(since = "1.4.0", feature = "array_default")]
        impl<T> Default for [T; $n] where T: Default {
            fn default() -> [T; $n] {
                [$t::default(), $($ts::default()),*]
            }
        }
        array_impl_default!{($n - 1), $($ts)*}
    };
    {$n:expr,} => {
        #[stable(since = "1.4.0", feature = "array_default")]
        impl<T> Default for [T; $n] {
            fn default() -> [T; $n] { [] }
        }
    };
}

array_impl_default!{32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T}