const_str/__ctfe/
to_char_array.rs

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pub struct ToCharArray<T>(pub T);

impl ToCharArray<&str> {
    pub const fn output_len(&self) -> usize {
        crate::utf8::str_count_chars(self.0)
    }

    pub const fn const_eval<const N: usize>(&self) -> [char; N] {
        crate::utf8::str_chars(self.0)
    }
}

/// Converts a string slice into an array of its characters.
///
/// This macro is [const-context only](./index.html#const-context-only).
///
/// # Examples
/// ```
/// const CHARS: [char; 5] = const_str::to_char_array!("Hello");
/// assert_eq!(CHARS, ['H', 'e', 'l', 'l', 'o']);
/// ```
///
#[macro_export]
macro_rules! to_char_array {
    ($s: expr) => {{
        const OUTPUT_LEN: usize = $crate::__ctfe::ToCharArray($s).output_len();
        const OUTPUT_BUF: [char; OUTPUT_LEN] =
            $crate::__ctfe::ToCharArray($s).const_eval::<OUTPUT_LEN>();
        OUTPUT_BUF
    }};
}