Interfaces

Abstract axes

ComponentArrays uses AbstractAxis values to associate named components with flat positions in an array. A custom axis subtype is appropriate when the component map is static and encoded in the subtype. Ordinary named layouts should use Axis.

An AbstractAxis subtype must provide an IdxMap type parameter whose keys are the accepted component names and whose values describe the corresponding flat positions or nested component metadata. The map is part of the type, so instances should not carry a second runtime copy of it.

The generic implementation supplies keys, symbol and Val indexing, multi-name indexing, firstindex, lastindex, and valkeys. A custom subtype should therefore usually only define the subtype and a zero-argument constructor. Its map must describe the same layout as the data passed to ComponentArray.

using ComponentArrays

struct TwoComponentAxis <: AbstractAxis{(left = 1, right = 2)} end

axis = TwoComponentAxis()
keys(axis), axis[Val(:left)], valkeys(axis)

((:left, :right), ComponentIndex(1, NullAxis()), (Val{:left}(), Val{:right}()))

The package tests this contract with an external subtype that defines no indexing or iteration methods of its own. This is the intended extension pattern for the interface.