Default operation for array items?

[pivotaljohn]

A common pain point (especially for the newly initiated) is the need to add an annotation to every &$!@ array item named in an overlay.

This is a sharp edge for folks learning about ytt, let alone overlays.

With Schema, all Data Values are about to become overlays (even the first Data Value document). This means for someone who is just using a ytt library, they'll have to know/learn that they need to include some kind of matcher+operation for every array item in a data value. This feels like an unduly steep learning curve.

In the same way that we assume @overlay/merge (-ish) as the default for map items...

What if the default operation of array items is overlay/append?

---

(last update: reflect results of design conversations from 2021-01-25)

[cppforlife]

alternative to consider here is replacing entire array (left side) with given array (right side).

^ this might be a less surprising behaviour and may be more familiar from other tools.

[pivotaljohn]

With no objection, here, and the driving need to make the UX around Schemas as smooth as we can, we're pulling the trigger on this: https://www.pivotaltracker.com/story/show/176489687.

[pivotaljohn]

There were objections — or at least a desire to unpack the implications of this idea. There was a design discussion circa week 4 of 2021.

TL;DR.

• an implied @overlay/replace on the containing array is problematic
  • created a break change.
  • when expressions are present on array items (i.e. the children of the array), that exclude those items, the overall behavior changes in undesirable ways.
• an implied @overlay/append on the array item avoids those problems.

[joaopapereira]

Created issue #269 to depict the result of this conversation