Both Arrays and Maps use similar syntax, so care is required to ensure the variable is of the correct datatype - this is determined by the first declaration line for the variable:

Using empty [ ] declares a Map:

Local $vVar[] ; A Map

Filling the [ ] with a dimension size declares an Array:

Local $vVar[3] ; An Array

Assigning element values when declaring makes the variable an Array - these three lines are functionally equivalent:

Local $vVar[3] = [1, 2, 3] ; An Array
Local $vVar[] = [1, 2, 3] ; An Array
Local $vVar = [1, 2, 3] ; An Array