https://wiki.tcl-lang.org/page/Feature+Request%3A+lappend+return+index

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On Thursday, August 11, 2022 at 11:01:31 AM UTC+2, aotto1 wrote:

https://wiki.tcl-lang.org/page/Feature+Request%3A+lappend+return+index

Before others will point out that wiki is the wrong tool, let me appreciate that you took your time to create a description with use case and examples :-)

Nevertheless, the specification is not complete as lappend can append more list items; which index should be returned?

Then:
* the index of the latest item is "end", i.e. {[lindex [lappend list $a] end] == $a}
* llength is a cheap operation because of Tcl's internal representation, you can get the value before and after lappend (and that also makes the code more readable imo)

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heinrichmartin <martin.heinrich@frequentis.com> wrote:

On Thursday, August 11, 2022 at 11:01:31 AM UTC+2, aotto1 wrote:

https://wiki.tcl-lang.org/page/Feature+Request%3A+lappend+return+index

Before others will point out that wiki is the wrong tool, let me
appreciate that you took your time to create a description with use
case and examples :-)

Nevertheless, the specification is not complete as lappend can append
more list items; which index should be returned?

Then:

* the index of the latest item is "end", i.e. {[lindex [lappend list
$a] end] == $a}

* llength is a cheap operation because of Tcl's internal
representation, you can get the value before and after lappend (and
that also makes the code more readable imo)

Further, for the specific case requested in the wiki article, there is
no need to maintain a separate variable, in the case of wanting the
index of the end element after lappend:

The LcConfigC_WriteHDL method just needs to be:

method LcConfigC_WriteHDL { hdl } {
my variable LcConfigC_Handle
lappend LcConfigC_Handle $hdl
return [expr {[llength $LcConfigC_Handle]-1}]
}

To get the index of the new "end" element.

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At Thu, 11 Aug 2022 13:15:48 -0000 (UTC) Rich <rich@example.invalid> wrote:

heinrichmartin <martin.heinrich@frequentis.com> wrote:

On Thursday, August 11, 2022 at 11:01:31 AM UTC+2, aotto1 wrote:

https://wiki.tcl-lang.org/page/Feature+Request%3A+lappend+return+index

Before others will point out that wiki is the wrong tool, let me
appreciate that you took your time to create a description with use
case and examples :-)

Nevertheless, the specification is not complete as lappend can append
more list items; which index should be returned?

Then:

* the index of the latest item is "end", i.e. {[lindex [lappend list
$a] end] == $a}

* llength is a cheap operation because of Tcl's internal
representation, you can get the value before and after lappend (and
that also makes the code more readable imo)

Further, for the specific case requested in the wiki article, there is
no need to maintain a separate variable, in the case of wanting the
index of the end element after lappend:

The LcConfigC_WriteHDL method just needs to be:

method LcConfigC_WriteHDL { hdl } {
my variable LcConfigC_Handle
lappend LcConfigC_Handle $hdl
return [expr {[llength $LcConfigC_Handle]-1}]
}

To get the index of the new "end" element.

Also: the index "end" is always the index of the last element of a list. The word end can be used anywhere a list index can be used:


lappend foo a b c
puts [lindex $foo end]





--
Robert Heller -- Cell: 413-658-7953 GV: 978-633-5364
Deepwoods Software -- Custom Software Services
http://www.deepsoft.com/ -- Linux Administration Services
heller@deepsoft.com -- Webhosting Services

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Robert Heller <heller@deepsoft.com> wrote:

At Thu, 11 Aug 2022 13:15:48 -0000 (UTC) Rich <rich@example.invalid> wrote:

heinrichmartin <martin.heinrich@frequentis.com> wrote:

On Thursday, August 11, 2022 at 11:01:31 AM UTC+2, aotto1 wrote:

https://wiki.tcl-lang.org/page/Feature+Request%3A+lappend+return+index

Before others will point out that wiki is the wrong tool, let me
appreciate that you took your time to create a description with use
case and examples :-)

Nevertheless, the specification is not complete as lappend can append
more list items; which index should be returned?

Then:

* the index of the latest item is "end", i.e. {[lindex [lappend list
$a] end] == $a}

* llength is a cheap operation because of Tcl's internal
representation, you can get the value before and after lappend (and
that also makes the code more readable imo)

Further, for the specific case requested in the wiki article, there is
no need to maintain a separate variable, in the case of wanting the
index of the end element after lappend:

The LcConfigC_WriteHDL method just needs to be:

method LcConfigC_WriteHDL { hdl } {
my variable LcConfigC_Handle
lappend LcConfigC_Handle $hdl
return [expr {[llength $LcConfigC_Handle]-1}]
}

To get the index of the new "end" element.

Also: the index "end" is always the index of the last element of a list. The word end can be used anywhere a list index can be used:

lappend foo a b c
puts [lindex $foo end]

Yes, but the OP's posting (and the wiki article) appears to be using
the numeric list position of the elements as a "handle" (in some ways
similar to libc file handle integers) to reference whatever it is the
list element references.

So for his use case he wants the numeric value of the new "end" so when
he attaches another new "end" his "handle" for the prior one does not
change position within the list.

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Hi, I want the *index* and *not* the *value* as return:

only possible solution is `expr {[llength $LcConfigC_Handle]-1}` but this only works well if one argument is appended
multiple arguments like `lappend -index varname a b c d` should return a list of indexes from position of "a b c d"


Robert Heller schrieb am Donnerstag, 11. August 2022 um 16:09:45 UTC+2:

At Thu, 11 Aug 2022 13:15:48 -0000 (UTC) Rich <ri...@example.invalid> wrote:

Also: the index "end" is always the index of the last element of a list. The word end can be used anywhere a list index can be used:

lappend foo a b c
puts [lindex $foo end]

--
Robert Heller -- Cell: 413-658-7953 GV: 978-633-5364
Deepwoods Software -- Custom Software Services
http://www.deepsoft.com/ -- Linux Administration Services
hel...@deepsoft.com -- Webhosting Services

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