# comfort-array: Arrays where the index type is a function of the shape type

[ bsd3, data-structures, library ] [ Propose Tags ]

Arrays from the basic array package are already very powerful compared with arrays in other languages. They may have any number of dimensions, are type safe and defined in a uniform way using the Ix class with free choice of the lower bounds (0, 1, or whatever you like).

This package goes one step further: The shape and the index type are different, but the index type is a type function of the shape type. This offers much more flexibility and type safety.

Some examples are:

• Range: Allow dynamic choice of lower and upper array bounds such as in the Arrays from the array package. You can combine it with other shapes in other dimensions. It allows you to describe the bounds of each dimension individually.

• Shifted: Describe array bounds by start index and length. It is sometimes more natural to use these parameters. E.g. a non-negative index type like Word cannot represent -1 and thus cannot encode an empty range starting with index 0.

• Square: An 2D array where both dimensions always have equal size.

• ZeroBased, OneBased: Arrays with fixed lower bound, either 0 or 1, respectively.

• (:+:): The Append type constructor allows to respresent block arrays, e.g. block matrices.

• Arrays with indices like LT, EQ, GT and dummy shape.

The lapack package defines even more fancy shapes like tall rectangular matrices, triangular matrices and banded matrices.