Why have I to rename before aliasing a command

[mauric...@gmail.com]

Hello,

I got a
'bad window path name ".f"
while executing
"pack .f"'
error with the following script.

package require Tk
frame .f
#rename ::.f ::_.f
proc myproc {args} {}
pack .f

The error vanished when I renamed the command (commented out line).
Can someone explain me what happened?
(I use Tk 8.4 and doz XP)

Thanks

ulis

[mauric...@gmail.com]

Sorry.
The complete script:

package require Tk
frame .f
#rename ::.f ::_.f

interp alias {} ::.f {} ::myproc

[stephan...@yahoo.fr]

Hi Maurice,

I tested it and saw that, each time you invoke interp alias, it causes
the aliased proc (or widget) to be destroyed.

proc a {arg} {puts a:$arg}
proc b {arg} {puts b:$arg}
# it works
puts [info body a]
interp alias {} ::a {} ::b
# error : a is not a procedure :
info body a

Regards,
Stéphane

[mauric...@gmail.com]

Many thanks for this info Stéphane.

It's strange that interp alias destroys the aliased command.
And it remains strange that pack .f uses the .f command.

ulis

[suchenwi]

Strange?
A command is either a C-coded one, a proc, or an alias. When you define
an alias named "foo", it deletes the previous instance. And in Tk, each
widget has a command with the same name. Removing such a command also
destroys the connected widget. Easily seen when you type, in an
interactive wish:
proc . args {puts hello}
The proc "." overwrites the widget command ".", which leads to its
destruction, and exit of the whole wish :-)

[mauric...@gmail.com]

lamentable

[Floria...@siemens.com]

lamentable? On the contrary!
See this beauty: I had some events that sent milli-seconds to my
programm and I had to cope with overflow of 32-bit ints. So I came up
with the following:

set WIDE_MAX_INT [expr {wide((1<<31)-1)}]
set wideUint [expr {wide(0)}]

proc wideUintP {a} {
if {$a<0} {
set ::wideUint [expr
{$::wideUint+$::WIDE_MAX_INT+$::WIDE_MAX_INT+2}]
interp alias {} ::wide_unsigned {} ::wideUintM
}
expr {wide($::wideUint+$a)}
}

proc wideUintM {a} {
if {$a>0} { interp alias {} ::wide_unsigned {} ::wideUintP }
expr {$::wideUint+$a}
}

interp alias {} ::wide_unsigned {} ::wideUintP

Now I can use [wide_unsigned $milli] without having to bother about
overflow anymore!
See how beautiful the two procs toggle.
And the best is, the implementation is so simple and efficient!