A special form of the for statement allows you to loop over all
the elements of a structure:
for [ val, key ] = expression
body
endfor
In this form of the for statement, the value of expression
must be a structure. If it is, key and val are set to the
name of the element and the corresponding value in turn, until there are
no more elements. For example,
x.a = 1
x.b = [1, 2; 3, 4]
x.c = "string"
for [val, key] = x
key
val
endfor
-| key = a
-| val = 1
-| key = b
-| val =
-|
-| 1 2
-| 3 4
-|
-| key = c
-| val = string
The elements are not accessed in any particular order. If you need to
cycle through the list in a particular way, you will have to use the
function struct_elements and sort the list yourself.
The key variable may also be omitted. If it is, the brackets are also optional. This is useful for cycling through the values of all the structure elements when the names of the elements do not need to be known.