TIP:            200
Title:          Listing the Values in an Array
Version:        $Revision: 1.4 $
Author:         Donal K. Fellows <donal.k.fellows@man.ac.uk>
Author:         Dossy Shiobara <dossy@panoptic.com>
State:          Rejected
Type:           Project
Vote:           Done
Created:        20-May-2004
Post-History:   
Keywords:       Tcl
Tcl-Version:    8.5

~ Abstract

This TIP proposes adding another subcommand to the '''array''' command
to list the values in an array.

~ Rationale

Currently, the easiest ways of building a list of all values within an
array involve either iterating over the names of the array elements
and then reading the value at each step, or iterating over the result
of '''array get''' and dropping the ''name'' part of each pair, as can
be seen from these code examples:

|set list {}
|foreach name [array names SomeArray] {
|   lappend list $SomeArray($name)
|}
|
|set list {}
|foreach {name value} [array get SomeArray] {
|   lappend list $value
|}

Neither of these is especially efficient, since the first does a very
large number of array reads, and the second builds a very large
intermediate list (particularly if you subsequently want to filter the
values to select a subset of them.)

It would be better if the functionality was added directly to the Tcl
core, especially as the conceptual overhead would be very low as there
are already subcommands of '''array''' for returning both the names of
the array and the name/value pairs.

~ Proposed Change

I propose to add a new subcommand to '''array''' called '''values'''
with the following syntax:

 > '''array values''' ''arrayName'' ?''globPattern''?

This returns a list of values that are contained in the array in the
"natural order" of the values within the array.  The optional
''globPattern'' argument allows for returning only some of the values
in the array (those values for keys that match the pattern according
to the rules of '''string match''').  The pattern will not change the
ordering of the list; it only filters the result.

The order of the values returned shall be such that the following two
'''foreach''' iterations shall behave identically (modulo traces on
the array variable):

|foreach {name value} [array get AnyArray $pattern] {
|   AnyScript
|}

|foreach name  [array names  AnyArray $pattern] \
|        value [array values AnyArray $pattern] {
|   AnyScript
|}

Note that this implies that the resulting list from '''array values'''
may well contain duplicates, and that none of the values actually
returned will necessarily match the supplied pattern.

~ Copyright

This document has been placed in the public domain.