start vs stop logic inconsistency

[vitaly-t]

We may have a bit of issue (or not) with the inconsistency: start logic is inclusive, while stop is exclusive, i.e. we start from the element that passes the predicate, but we stop with the element that's prior to the predicate that passed.

Should they not be both inclusive or exclusive?

@RebeccaStevens What do you think?

[vitaly-t]

I've tried to compare the logic to RXJS (where it uses a predicate):

• skipWhile is inclusive
• takeWhile is exclusive

So that doesn't help much, though if we follow their logic in the Recipes, then it is consistent with how we do it:

• skipWhile(predicate) => start(!predicate) => inclusive
• takeWhile(predicate) => stop(!predicate) => exclusive

[vitaly-t]

The problem that I'm seeing now is linguistic. It makes perfect sense why skipWhile logic produces inclusive result, and why takeWhile produces exclusive result. But with the start and stop operators it is absolutely not clear, and you can assume it either way.

This brings the idea of adding skipWhile + takeWhile, and retiring start and stop operators.

[vitaly-t]

new operators have been added, and now in master:

• Operator skipWhile added, and operator start marked deprecated
• Operator takeWhile added, and operator stop marked deprecated

[vitaly-t]

v2.4.0 now has the new operators.

The old operators will be removed in v3.0.0, as it will be a breaking change.

[vitaly-t]

TODO: Need to revisit the inclusive/exclusive logic added by skipUntil and takeUntil, to see if they are needed.

UPDATE

Here's what I found, after many tests and analysis...

• takeWhile must always be exclusive, based on linguistic logic (done)
• skipWhile must always be inclusive, based on linguistic logic (done)

The until logic is supposed to complete the scope by reversing that:

• takeUntil must be inclusive
• skipUntil must be exclusive

Then we would have a complete logical range. ☝️

CONCLUSION

We do need to add inclusive takeUntil and exclusive skipUntil, to complete our logical range. 🔖

[vitaly-t]

I did not feel sure about this, so I have posted a question.

[vitaly-t]

Looks like my assumption was correct after all, and until must be treated as check after, which makes takeUntil inclusive, and skipUntil exclusive.

[vitaly-t]

New operator takeUntil merged into the master.

[vitaly-t]

New operator skipUntil merged into the master.

[vitaly-t]

v2.5.0-beta.0 released with all 4 new operators.

[vitaly-t]

v2.5.0 release completed this task.