Re: The best way to copy a list?

On Wed, 18 Jun 2025 17:03:36 +0530, Ashok wrote:

Not sure I understand the question. Why not just
 
set b $a
 
?
 
Also, your code will not always give identical results using expr ([expr
{$x}] is not always $x). For example,
 
% set a {a 0x10 b}
a 0x10 b % set b [lmap x $a {expr {$x}}]
a 16 b
 
You could use one of the following forms instead
 
% set b [lmap x $a {lindex $x}]
a 0x10 b % set b [lmap x $a {string cat $x}]
a 0x10 b % set b [lmap x $a {return -level 0 $x}]
a 0x10 b
 
but as I said, why not just set a $b ?
 
/Ashok
 
set a {a 0x10 b}
On 6/18/2025 12:49 PM, Mark Summerfield wrote:

Is using `lmap` the best way to copy a list? For example:
 
     package require struct::list 1 set a {a bc def ghij klmno}
     # is the following the best way to copy a list?
     set b [lmap x $a {expr {$x}}]
     puts "a={$a} b={$b} a==b=[struct::list equal $a $b]"
 
Output:
 
     a={a bc def ghij klmno} b={a bc def ghij klmno} a==b=1

I'm coming to Tcl from Python & Go. In Python saying `a = [1, 2, 3]` and
then `b = a` makes `b` a _reference_ to `a` rather than an independent
variable. Now I realise that Tcl doesn't do it that way and that `set a
$b` works fine.