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#[macro_export]
macro_rules! new_flattened {
    ($value:expr, $container:ident) => {
        $container::new($value)
    };
    ($value:expr, $container:ident, $($containers:ident),+) => {
        $container::new(new_flattened!($value, $($containers),+))
    };
}

#[cfg(test)]
mod tests {
    #[test]
    fn simple() {
        assert_eq!(
            Box::new(Box::new(Box::new(5))),
            new_flattened!(5, Box, Box, Box),
        );
    }
}