The documentation for the [rename] command, used to rename Tcl procs, is available at http://purl.org/tcl/home/man/tcl8.5/TclCmd/rename.htm .
The [rename] command is most often used for wrapping commands. In other words, the programmer uses [rename] to hide another command -- so that a wrapper can be placed around the hidden command to change its behavior. Examples of this important concept abound on the Wiki; among the clearest are: DGP: Be aware that if you rename a command into another
[Discuss examples. Explain errorInfo subtleties (refer to live examples). Explain "return [eval ::_$original_command \$first_argument $args]" idiom.]
RS Another frequent application for rename is to remove commands, by renaming them to the empty string:
rename foo {}
DGP Be aware that if you [rename] a command into another namespace, its evaluation context will change to that namespace. HaO 2010-04-10: (discussion on CLT ): rename or delete from inside targeted proc is allowed:
% namespace eval one {
variable message "I'm in one"
proc test {} {variable message; return $message}
}
% namespace eval two {variable message "I'm in two"}
% rename one::test two::test
% two::test
I'm in twoGDE What's the recommended way to test for the pre-existence of the "destination" argument proc to avoid an error at runtime? The best I could come up with is:
if {![llength [info commands new_proc_name]]} {
rename old_proc_name new_proc_name
}MJ - The way to avoid the error is to use [catch], this is in line with the view that you shouldn't check if you can do something, but just do it (and handle errors):
if {[catch {rename old new}]} {
# handle error because new already exists
} GDE What if I actually do care about the error? In other words, I don't want to do the rename if I've already done it?
(By way of context: this is in a script that may repeatedly get sourced into a single interpreter during a debug session. The first rename creates a backup of the "production" version of the proc then the rest of the script redefines a wrapper around that production version. The user may then edit the debug script to further refine the wrapper proc and re-source, but the catch method will then create a wrapper around the wrapper around the original, rather than just redefining the first wrapper.)
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