Changing a rule input variable in a child interface changes it in the parent but SAIL in local variable doesn't?

Question

Just a question regarding the exact location and order that variable data is saved in. I have noticed that saving a variable in a child interface that was passed into it as a rule input also changes the related local variable in the parent interface, which is normal functionality that is explained in several tutorials. However I also noticed that saving a set of identical SAIL code into a local variable and then changing another local variable results in no change. For example if a dropdown option like this were selected it immediately resets the variable, local!madeFromCDT , back to the default: local!madeFromCDT : cast( typeof(type!("arbitraryType"), {abitraryField: null}))), 
 local!sailInterfaceDropdown: a!sideBySideLayout( item: rule!nestedDropdownfield( choiceLabels: local!listOfYesNo choiceValues: local!listOfYesNo value: index( local!madeFromCDT , "arbitraryField" saveInto: a!save( local!madeFromCDT , updatedictionary( dictionary: local! madeFromCDT , fieldsAndValues: {arbitraryField: save!value} ) ) ) ) However, using a expression rule does permanently change the local variable, local!madeFromCDT : local!madeFromCDT : cast( typeof(type!("arbitraryType"), {abitraryField: null}))), rule!sameSAILDropDownButInExpressionRule( madeFromCDT: local!madeFromCDT )

Mike Schmitt · Answer

francoh7128 said: using a expression rule does permanently 
 "does" or "doesn't"? It sounds like you meant to say "doesn't" but it's a little ambiguous. 
 If you declare interface components in a local variable, strange things can and will happen sometimes. You CAN (usually) get it to work, however, but I believe the code in the local variable must be manually declared using a Refresh Variable set to "REFRESH ALWAYS" behavior. local!sailInterfaceDropdown: a!refreshVariable(
 value: a!sideBySideLayout(
 item: rule!nestedDropdownfield(
 choiceLabels: local!listOfYesNo
 choiceValues: local!listOfYesNo
 value: index(
 local!madeFromCDT,
 "arbitraryField"
 saveInto: a!save(
 local!madeFromCDT,
 updatedictionary(
 dictionary: local!madeFromCDT,
 fieldsAndValues: {arbitraryField: save!value}
 )
 )
 )
 )
 ),
 refreshAlways: true()
) 
 Additionally, since this manually references the earlier local variable, it's not clear what would happen if, for instance, you then try to reference this local variable multiple times within an interface. It might just break, or do something even more unexpected. Generally I avoid doing this except for when I have static UI elements I want to use several times on a form without having to manually declare them everywhere, but even then they only reference generic external variables (like simply saving a single value into a single rule input, like a submit button or similar).

Changing a rule input variable in a child interface changes it in the parent but SAIL in local variable doesn't?

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