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From: Mark Summerfield <m.n.summerfield@gmail.com>
Newsgroups: comp.lang.tcl
Subject: Re: The best way to copy a list?
Date: Wed, 18 Jun 2025 11:59:04 -0000 (UTC)
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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.