> Tcl arrays are associative. Tcl has pretty much 3 data structures:
>
> - scalars
> - lists
> - arrays (which are associative)
>
> The trick is that a list is really just a scalar with whitespace between
> the elements, unless the element is enclosed by braces, so there's really
> only two.
Woah, that last part isn't true at all, and is a common misconception
that leads people to think Tcl isn't up-to-snuff, which isn't true.
Lists are preserved in Tcl as arrays of Tcl_Obj's. If I do the following:
proc makeList {size} {
set output ""
for {set i 0} {$i < $size} {incr i} {
lappend output $i
}
return $output
}
set myList [makeList 50]
I will not have a *single* byte in memory reserved for a char. I will
have a Tcl_Obj *objv[50] where each Tcl_Obj is an Integer object. I
*can* then say:
puts $myList
and that will cause the whole thing to create a string representation
of each object (the list and each integer respectively). If I do:
set otherList $myList
I don't create any new objects - I increment the reference count of the
original list by one and point to that. If I then modify the original
list, then otherList will be left with the original (lazy copy-on-write
semantics).
That means that list's lindex accessor is O(1) and appends are O(1)
except where we need to increase the C Tcl_Obj **objv array (and that
only needs to copy the pointers).
Jeff Hobbs The Tcl Guy
Senior Developer http://www.ActiveState.com/
Tcl Support and Productivity Solutions
