[EEZ Flow] Deep comparison of Structs and Watch on Struct member changes

[dhugoexe]

Context

I'm building a Flow that needs to detect whether a Struct variable has been
edited by the user (e.g. a config sub-struct), by
comparing a saved snapshot against the current live value, and re-evaluating
whenever any member of the struct changes.

Questions

1. Struct equality with Compare (= operator)
   Does the Compare action's = operator perform a deep, member-by-member
   comparison when both operands are of type Struct, or does it compare by
   reference ? The docs (P8. Variables) don't specify this.

2. Assignment semantics for Structs (SetVariable)
   When doing SetVariable myVar <- otherStructVar, is the resulting value a
   deep copy, or a reference to the same underlying struct instance?

3. Watching changes on a whole Struct
   The Watch component docs describe monitoring "the value of the
   variable" — is it possible to Watch an entire Struct variable and get
   notified if any member changes, or is Watch limited to scalar/leaf
   values, requiring one Watch per member?

Why this matters

This is a common pattern (dirty-state / "unsaved changes" detection on a
config form bound to a struct) and the docs don't currently clarify whether
struct comparison, copy, and watch semantics support it out of the box, or
whether member-by-member workarounds are required.

Thanks,

[mvladic]

1. Struct equality with Compare (= operator) ...

It compares by reference.

2. Assignment semantics for Structs (SetVariable) ...

It assigns reference to the same struct instance. Use SetVariable myVar <- Array.clone(otherStructOrArrayVar) to make a deep copy.

3. Watching changes on a whole Struct ...

Not possible to watch an entire Struct variable and get notified if any member changes.

This is a common pattern (dirty-state / "unsaved changes" detection on a config form bound to a struct)...

So, only point no. 2 is covered for this use case.

[mvladic]

[EDITED]

I added expression function Array.isEqual to perform a deep, member-by-member comparison of two array or struct variables.

Functions Array.clone and Array.isEqual also works for struct variables because internally struct variables are stored as arrays. But, to avoid confusion I also added Struct.clone and Struct.isEqual as aliases to Array.clone and Array.isEqual.

So, in your case, you can use Struct.isEqual to find out if the item under edit is modified compared to the original item, for example like this:

Or you can just set Disabled state of the Save button like this: