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use crate::ascii;

#[cfg(not(test))]
impl<const N: usize> [u8; N] {
    /// 将此字节数组转换为 ASCII 字符数组，如果任何字符为非 ASCII，则返回 `None`。
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(ascii_char)]
    /// #![feature(const_option)]
    ///
    /// const HEX_DIGITS: [std::ascii::Char; 16] =
    ///     *b"0123456789abcdef".as_ascii().unwrap();
    ///
    /// assert_eq!(HEX_DIGITS[1].as_str(), "1");
    /// assert_eq!(HEX_DIGITS[10].as_str(), "a");
    /// ```
    #[unstable(feature = "ascii_char", issue = "110998")]
    #[must_use]
    #[inline]
    pub const fn as_ascii(&self) -> Option<&[ascii::Char; N]> {
        if self.is_ascii() {
            // SAFETY: 刚刚检查它是 ASCII
            Some(unsafe { self.as_ascii_unchecked() })
        } else {
            None
        }
    }

    /// 将此字节数组转换为 ASCII 字符数组，而不检查它们是否有效。
    ///
    ///
    /// # Safety
    ///
    /// 数组中的每个字节都必须在 `0..=127` 中，否则就是 UB。
    #[unstable(feature = "ascii_char", issue = "110998")]
    #[must_use]
    #[inline]
    pub const unsafe fn as_ascii_unchecked(&self) -> &[ascii::Char; N] {
        let byte_ptr: *const [u8; N] = self;
        let ascii_ptr = byte_ptr as *const [ascii::Char; N];
        // SAFETY: 调用者承诺所有字节都是 ASCII
        unsafe { &*ascii_ptr }
    }
}