WISH: finer control over reactive relations triggered by pairs

[hiiamboris]

I find it often a case where a reaction should be only placed on x or y coordinate of face's offset, size or custom pair dimension.

However, reactivity does not provide this flexibility: place a reaction on /x and it will be triggered by a change in /y. (Not just reactivity, on-deep-change does not provide this info either)

Not only this produces unneeded reactions, but also prevents one from creating flexible resize scenarios, e.g. what if I want to set /y to a default, but only if it wasn't explicitly set to another value?

default: 10
r: deep-reactor [
    s: 1x1
    react [
        [self/s/x]                          ;) s/x serves as a reaction source
        triggered-by-SX: yes                ;) NO WAY TO KNOW THIS!!
        if triggered-by-SX [s/y: default]   ;) otherwise I wanna leave s/y as is - how?
        ?? s
    ]
]
r/s/x: 2
r/s/y: 3

Output:

s: 1x10
s: 2x10
s: 2x10        ;) I want 2x3 here

[dockimbel]

After the changes made by on-deep-fixes branch, pair individual component setting will trigger a on-change reaction (and no more on-deep-change). That was necessary as the deep change handler is really meant for series. OTOH, the value change handler spec does not allow to pass the information about which component was changed. So I think that the on-change spec should be extended to pass the value's component name, when applicable.

[hiiamboris]

Like on-change [subject [word! path!] old [any-type!] new [any-type!]] ?

[dockimbel]

That's one option, another one is just to add an extra field [word! none!] argument.