Re: New aggregates with Ada 2022.

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

On 2022-06-29 13:06, Niklas Holsti wrote:
> On 2022-06-29 11:30, Jeffrey R.Carter wrote:
>>
>> * Maps are usually constrained. It does not make sense to concatenate, sort, 
>> slice, or slide a map.
> 
> In mathematics, maps (functions) are often sliced, in other words restricted to 
> a subset of their full domain. They are also often concatenated, in the sense of 
> combining functions defined on separate domain sets into a combined function 
> defined on the union of those separate domain sets. Those operations would be 
> useful in programs too.
> 
> The essential aspect of maps and map operations is that there is no "sliding" 
> that changes the relationship of domain values (keys) with range values.
> 
> That said, it very often makes sense to provide sorted access to the elements of 
> a map, sorted by some criterion, while maintaining the relationship of keys and 
> their mapped values. That might be seen as sorting the map into a sequence (as 
> described below).

Perhaps I could have been clearer. I mean that it doesn't make sense to 
concatenate, sort, slice, or slide an array used as a map. For example, if we 
represent a map Character => Natural as

type Char_Count_Map is array (Character) of Natural;
Map : Char_Count_Map;

and want a map with the domain restricted to the ASCII letters, both capital and 
small,

Map ('A' .. 'Z') & Map ('a' ..'z')

doesn't do what we want.

You are talking about the abstraction of a map in general, and the operations 
you describe are different from the array operations I was talking about.

-- 
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