TIP #200: Listing the Values in an Array
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TIP:	200
Title:	Listing the Values in an Array
Version:	$Revision: 1.4 $
Authors:	Donal K. Fellows <donal.k.fellows@man.ac.uk>
	Dossy Shiobara <dossy@panoptic.com>
State:	Rejected
Type:	Project
Tcl-Version:	8.5
Vote:	Done
Created:	Thu May 20 00:00:00 UTC 2004
Keywords:	Tcl
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] \par        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.
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