Macro arr 

macro_rules! arr {
    ($([$([$($elems:expr),+]),+]),+ $(,)?) => { ... };
    ($([$($elems:expr),+]),+ $(,)?) => { ... };
    ($($elem:expr),+ $(,)?) => { ... };
}

The arr! macro is designed to accept arrays of depth 1D, 2D and 3D and flatten them into a single-dimensional vector. It also tracks and stores the shape (dimensions) of the array, which includes the number of rows, columns, and further dimensions as needed.