Macro dim4 

macro_rules! dim4 {
    ($dim0:expr) => { ... };
    ($dim0:expr, $dim1:expr) => { ... };
    ($dim0:expr, $dim1:expr, $dim2:expr) => { ... };
    ($dim0:expr, $dim1:expr, $dim2:expr, $dim3:expr) => { ... };
}

Create a dim4 object from provided dimensions

The user can pass 1 or more sizes and the left over values will default to 1.