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//! This crate implements a structure that can be used as a generic array type.use
//! Core Rust array types `[T; N]` can't be used generically with respect to `N`, so for example this:
//!
//! ```{should_fail}
//! struct Foo<T, N> {
//!     data: [T; N]
//! }
//! ``` 
//!
//! won't work.
//!
//! **generic-array** exports a `GenericArray<T,N>` type, which lets the above be implemented as:
//!
//! ```
//!# use generic_array::{ArrayLength, GenericArray};
//! struct Foo<T, N: ArrayLength<T>> {
//!     data: GenericArray<T,N>
//! }
//! ``` 
//!
//! The `ArrayLength<T>` trait is implemented by default for [unsigned integer types](../typenum/uint/index.html) from [typenum](../typenum/index.html).
//!
//! For ease of use, an `arr!` macro is provided - example below:
//!
//! ```
//! # #[macro_use] 
//! # extern crate generic_array;
//! # extern crate typenum;
//! # fn main() {
//! let array = arr![u32; 1, 2, 3];
//! assert_eq!(array[2], 3);
//! # }
//! ```
#![cfg_attr(feature="no_std", no_std)]
#[cfg(feature="no_std")]
extern crate core as std;
extern crate typenum;
pub mod arr;
use typenum::uint::{Unsigned, UTerm, UInt};
use typenum::bit::{B0, B1};
use std::marker::PhantomData;
use std::mem;
use std::ops::{Deref, DerefMut};
use std::ptr;
use std::slice;

/// Trait making GenericArray work, marking types to be used as length of an array
pub unsafe trait ArrayLength<T> : Unsigned {
    /// Associated type representing the array type for the number
    type ArrayType;
}

unsafe impl<T> ArrayLength<T> for UTerm {
    type ArrayType = ();
}

/// Internal type used to generate a struct of appropriate size
#[allow(dead_code)]
#[repr(C)]
pub struct GenericArrayImplEven<T, U> {
    parent1: U,
    parent2: U,
    _marker: PhantomData<T>
}

impl<T: Clone, U: Clone> Clone for GenericArrayImplEven<T, U> {
    fn clone(&self) -> GenericArrayImplEven<T, U> {
        GenericArrayImplEven {
            parent1: self.parent1.clone(),
            parent2: self.parent2.clone(),
            _marker: PhantomData
        }
    }
}

impl<T: Copy, U: Copy> Copy for GenericArrayImplEven<T, U> {}

/// Internal type used to generate a struct of appropriate size
#[allow(dead_code)]
#[repr(C)]
pub struct GenericArrayImplOdd<T, U> {
    parent1: U,
    parent2: U,
    data: T
}

impl<T: Clone, U: Clone> Clone for GenericArrayImplOdd<T, U> {
    fn clone(&self) -> GenericArrayImplOdd<T, U> {
        GenericArrayImplOdd {
            parent1: self.parent1.clone(),
            parent2: self.parent2.clone(),
            data: self.data.clone()
        }
    }
}

impl<T: Copy, U: Copy> Copy for GenericArrayImplOdd<T, U> {}

unsafe impl<T, N: ArrayLength<T>> ArrayLength<T> for UInt<N, B0> {
    type ArrayType = GenericArrayImplEven<T, N::ArrayType>;
}

unsafe impl<T, N: ArrayLength<T>> ArrayLength<T> for UInt<N, B1> {
    type ArrayType = GenericArrayImplOdd<T, N::ArrayType>;
}

/// Struct representing a generic array - GenericArray<T, N> works like [T; N]
#[allow(dead_code)]
pub struct GenericArray<T, U: ArrayLength<T>> {
    data: U::ArrayType
}

impl<T, N> Deref for GenericArray<T, N> where N: ArrayLength<T> {
    type Target = [T];

    fn deref(&self) -> &[T] {
        unsafe {
            slice::from_raw_parts(self as *const Self as *const T, N::to_usize())
        }
    }
}

impl<T, N> DerefMut for GenericArray<T, N> where N: ArrayLength<T> {
    fn deref_mut(&mut self) -> &mut [T] {
        unsafe {
            slice::from_raw_parts_mut(self as *mut Self as *mut T, N::to_usize())
        }
    }
}

impl<T: Default, N> GenericArray<T, N> where N: ArrayLength<T> {

    /// Function constructing an array filled with default values
    pub fn new() -> GenericArray<T, N> {
        unsafe {
            let mut res: GenericArray<T, N> = mem::uninitialized();
            for r in res.iter_mut() { ptr::write(r, T::default()) }
            res
        }
    }

}

impl<T: Clone, N> GenericArray<T, N> where N: ArrayLength<T> {

    /// Function constructing an array from a slice; the length of the slice must be equal to the length of the array
    pub fn from_slice(list: &[T]) -> GenericArray<T, N> {
        assert_eq!(list.len(), N::to_usize());
        unsafe {
            let mut res: GenericArray<T, N> = mem::uninitialized();
            for i in 0..N::to_usize() { ptr::write(&mut res[i], list[i].clone()) }
            res
        }
    }

}

impl<T: Clone, N> Clone for GenericArray<T, N> where N: ArrayLength<T> {
    fn clone(&self) -> GenericArray<T, N> {
        unsafe {
            let mut res: GenericArray<T, N> = mem::uninitialized();
            for i in 0..N::to_usize() { ptr::write(&mut res[i], self[i].clone()) }
            res
        }
    }
}
impl<T: Copy, N> Copy for GenericArray<T, N> where N: ArrayLength<T>, N::ArrayType: Copy {}