Re: New aggregates with Ada 2022.

["Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>]

On 2022-06-29 06:01, Randy Brukardt wrote:
> 
> But there is (or shouldn't be) anything special about a one-dimensional
> array (presuming you intend to allow arrays with more dimensions). And the
> "abstraction" you talk about is selecting a bunch of barely related elements
> from a multi-dimensional array.

Arrays are usually used to implement map, (mathematical) matrices and vectors, 
or sequences. Each usage tends to have unique features:

* Maps are usually constrained. It does not make sense to concatenate, sort, 
slice, or slide a map. The abstraction of a map includes non-discrete key 
subtypes, so arrays used as maps are a special case.

* Matrices have component types that behave like numbers. The mathematical 
definition of matrices includes integer indices with a lower bound of 1. Vectors 
are usually considered to be matrices of one column ("column vector") which can 
be transposed to obtain matrices of one row ("row vector").

* Sequences are usually unconstrained. Typical discussion of sequences outside 
of programming use integer values to indicate positions, using terms such as the 
first thing in a sequence, the second thing, ..., so indices should be of an 
integer type with a lower bound of 1. It sometimes makes sense to concatenate, 
sort, slice, or slide sequences.

A language that provided direct support for these abstractions should not need 
to provide arrays.

-- 
Jeff Carter
"[T]he language [Ada] incorporates many excellent structural
features which have proved their value in many precursor
languages ..."
C. A. R. Hoare
180