Re: Array get element with default (no error if not exist)

On Fri, 16 Aug 2024 07:10:30 +0000
RodionGork <rodiongork@github.com> wrote:

Hi Friends!
 
Still making my first feeble steps in TCL so please excuse me if this is
naive or was asked multiple times.
 
Attempt to fetch by non-existing key in "associative array" results in
error, e.g.
 
set a(1) 5
puts $a(2) ;# yields error
 
the workaround seems to be [info exists ::a(2)] which feels a bit remote
from other "array" commands.
 
Is there some motivation why some command for get-with-default is not
implemented, e.g.
 
puts [array peek $a 2 "default value"]
 
Popular use-case for this would be creating map where elements are
updated (like counter of words etc) - though I found this is cleverly
covered by "incr" and "append" commands properly behaving
when element to be incremented or appended does not exist yet.
 
But I suspect there are other situations when such a command may be
handy.

Already there in 8.7/9.0

% array default set foo NOSUCHVALUE
% set foo(1)
NOSUCHVALUE
% info exists foo(1)
0

8.7/9.0 also adds [dict getwithdefault] (aka [dict getdef]) for dict
values.

Also why [array exists ...] command does not exist (while [dict exists
..] does)? Perhaps there is something about no good syntax for it due
to how arrays are implemented?

The [array exists] command is there since ... forever

% array exists foo
1
% array exists nosucharray
0

Well, at least since 8.4 . See https://www.tcl-lang.org/man/tcl8.4/TclCmd/array.htm

--
Emiliano