Arrays and maps: consistency

[ChristianGruen]

Suggestions (based on #1338, related: #1868)

1. In symmetry with the pairs lookup specifier, we should add array:pairs and an inverse array:of-pairs function.
2. In symmetry with the values lookup specifier, we should add array:values and map:values functions, to retrieve the values of maps and the members of arrays in a sequence of arrays.
3. In return, array:members and array:of-members seem redundant, and we should drop them.
4. In analogy with the keys specifier and map:keys, we should add array:keys (which returns a dense integer range).

Background

With version 4.0, we are adding a lot of promising and powerful new map and array features. This is a big step forward, compared to the obvious limitations of 3.1.

Some aspects of the 3.1 design have made it difficult (or impossible) to fully adjust array and maps, but (in my opinion) the old overall concept was impressively consistent – and it is definitely a big challenge to achieve a 4.0 design that is not too fragmented.

To me, this becomes particularly evident in the case of arrays. The following example sums up the items of all members of an array. For the cumbersome 3.1 solution…

for $pos in 1 to array:size($array)
return sum($array($pos))

…we now have several (roughly?) equivalent options to do this:

1. for member $m in $array return sum($m)
2. array:members($array) ! sum(?value)
3. $array?pairs::* ! sum(?value)
4. $array?values::* ! sum(.)

The examples above imply that:

• for 1., an array member is a sequence;
• for 2., an array member is a map;
• for 3., an array has pairs (but there is no array:pairs);
• for 4., an array has values (but there is no array:values).

[dnovatchev]

Suggestions (based on #1338, related: #1868)

1. In symmetry with the pairs lookup specifier, we should add array:pairs and an inverse array:of-pairs function.

We already have the numbered-item record which serves exactly this purpose (the mentioned above array:pairs). Therefore, in order to avoid clutter and pollution, we could reuse this record and have: array:numbered-items, and array:from-numbered-items

3. In symmetry with the values lookup specifier, we should add array:values and map:values functions, to retrieve the values of maps and the members of arrays in a sequence of arrays.

4. In return, array:members and array:of-members seem redundant, and we should drop them.

6. In analogy with the keys specifier and map:keys, we should add array:keys (which returns a dense integer range).

This seems quite unnecessary, because we already have array:size. If it was allowed to have any integer as the first and last index of an array, then a useful function would be array:bounds

[ChristianGruen]

Note that the main intent of this issue is consistency, i.e. to bring maps and arrays closer together, and to align array terminology with the key specifiers of the lookup operator, which allows you to retrieve “pairs”, “keys” and “values” of arrays (see https://qt4cg.org/specifications/xquery-40/xpath-40.html#id-postfix-lookup).