Assignment to local variables in Expression rule

There are mainly only 2 places where you can "assign a value" to a local variable:

1) at declaration

2) as the result of a user interaction in an interface component

Seeing as this is an expression rule, and therefore #2 is irrelevant, you will need to assign the value at declaration (#1). 

This is the most important concept here: There is no such thing, in Appian's expression language, as "define a blank local variable then in a later line of code give it a new value".  If you know its initial value, then you will assign it at creation time.

I think maybe having that variable being the key in the dictionary might be doing weird things.

Try this:

a!localVariables(
  local!parts: {
    a!map(
      partName: "part1",
      quantity: 1,
      unitCost: 1
    ),
    a!map(
      partName: "part2",
      quantity: 1,
      unitCost: 1
    )

  },
  {
    parts: local!parts,
    length: length(local!parts)
  }
)

Thanks Mike for your input. 

  If you know its initial value, then you will assign it at creation time. --  what if I don't know the value of the variable during initialization and the value would come after initialization as a result of some equation like we do in traditional programming. how to handle such scenarios.

Vasudeva said:

the value would come after initialization as a result of some equation

You would declare its value after any other calculations (usually declared as their own local variables) on which it depends.

ok, so the rule of thumb is to initialize the local variable during declaration it self. Got it, thanks

basically, yes.

Where can I find more info on this, I have tried the expression section of the Appian documentation, but I couldn't find any thing, I'm looking for examples and howtos.. 

I have referred to this -> docs.appian.com/.../Expressions.html

The local variables section pretty much covers it.

docs.appian.com/.../Local_Variables.html

thank you will go through it... really this is a wonderful community