//! Extensions

pub trait Tuple2Ext<T, U>
{
    fn swap(self) -> (U, T);
}

impl<T, U> Tuple2Ext<T, U> for (T, U)
{
    #[inline(always)]
    fn swap(self) -> (U, T) {
	(self.1, self.0)
    }
}

#[inline(always)] 
pub fn is_utf8_char_boundary(byte: u8) -> bool
{
    //! 
    //! Copied from stdlib
    (byte as i8) >= -0x40
}

pub trait StrExt
{
    fn floor_char_boundary_impl(&self, index: usize) -> usize;
}

impl<T: ?Sized + AsRef<str>> StrExt for T
{
    #[inline] 
    fn floor_char_boundary_impl(&self, index: usize) -> usize {
	//!
	//! copied from stdlib
	let this = self.as_ref();
	if index >= this.len() {
	    this.len()
	} else {
	    let lower_bound = index.saturating_sub(3);
	    let new_index = this.as_bytes()[lower_bound..=index]
		.iter()
		.rposition(|&b| is_utf8_char_boundary(b));
	    
	    // SAFETY: we know that the character boundary will be within four bytes
            unsafe { lower_bound + new_index.unwrap_unchecked() }
	}
    }
}