//! Utils

pub trait NewCapacity: Sized
{
    fn new() -> Self;
    fn with_capacity(cap: usize) -> Self;
}

impl NewCapacity for String
{
    fn new() -> Self
    {
	Self::new()
    }
    
    fn with_capacity(cap: usize) -> Self
    {
	Self::with_capacity(cap)
    }
}

impl<T> NewCapacity for Vec<T>
{
    fn new() -> Self
    {
	Self::new()
    }
    
    fn with_capacity(cap: usize) -> Self
    {
	Self::with_capacity(cap)
    }
}

pub fn hint_cap<T: NewCapacity, I: Iterator>(iter: &I) -> T
{
    match iter.size_hint() {
	(0, Some(0)) | (0, None) => T::new(),
	(_, Some(x)) | (x, _) => T::with_capacity(x)
    }
}

#[macro_export] macro_rules! opaque_error {
    ($msg:literal) => {
	{
	    #[derive(Debug)]
	    struct OpaqueError;

	    impl ::std::error::Error for OpaqueError{}
	    impl ::std::fmt::Display for OpaqueError
	    {
		fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result
		{
		    write!(f, $msg)
		}
	    }
	    OpaqueError
	}
    };
    ($msg:literal $($tt:tt)*) => {
	{
	    #[derive(Debug)]
	    struct OpaqueError(String);

	    impl ::std::error::Error for OpaqueError{}
	    impl ::std::fmt::Display for OpaqueError
	    {
		fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result
		{
		    write!(f, "{}", self.0)
		}
	    }
	    OpaqueError(format!($msg $($tt)*))
	}
    };
    (yield $msg:literal $($tt:tt)*) => {
	{
	    #[derive(Debug)]
	    struct OpaqueError<'a>(fmt::Arguments<'a>);

	    impl ::std::error::Error for OpaqueError{}
	    impl ::std::fmt::Display for OpaqueError
	    {
		fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result
		{
		    write!(f, "{}", self.0)
		}
	    }
	    OpaqueError(format_args!($msg $($tt)*))
	}
    };
}