[Tcl-bugs] [ tcl-Bugs-707104 ] [interp alias] commands cannot be [rename]d

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Bugs item #707104, was opened at 2003-03-20 21:05
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Category: 19. [interp]
Group: None
Status: Open
Resolution: Duplicate
Priority: 2
Submitted By: Vince Darley (vincentdarley)
Assigned to: miguel sofer (msofer)
Summary: [interp alias] commands cannot be [rename]d

Initial Comment:
I see some very peculiar behaviour with aliased 
commands, which is at the very least not 
documented, and possible a bug:

% proc foo {} { puts "orig" }
% interp alias {} bar {} foo
% bar
orig
% rename bar bar2
% bar2
orig
% bar
orig
# (So now both 'bar' and 'bar2' are aliases, 
i.e. 'rename' actually copies the alias rather than 
renaming it)

% proc foo2 {} { puts "new" }
% interp alias {} bar {} foo2
% bar
new
% bar2
invalid command name "bar2"

# (So the act of creating a new alias "bar" deletes 
both the old aliases "bar" and "bar2")




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Comment By: Eric Boudaillier (beric)
Date: 2003-03-21 10:56

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Does this help ? It takes care of renaming an alias (restricted 
in one interp)

proc rename_alias {oldCmd newCmd} {
    set alias [interp alias {} $oldCmd]
    if {[llength $alias]} {
        if {$newCmd ne ""} {
            eval [concat [list interp alias {} $newCmd {}] $alias]
        }
        interp alias {} $oldCmd {}
    } else {
        rename $oldCmd $newCmd
    }
}



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Comment By: Donal K. Fellows (dkf)
Date: 2003-03-21 10:45

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I agree with Vince here, especially now we've got command
traces.

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Comment By: Vince Darley (vincentdarley)
Date: 2003-03-21 09:48

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The 'rename' man page needs updating then to reflect this limitation.  It's 
a shame that aliases don't work in this way, since they are otherwise a 
very powerful part of Tcl.  However, they completely break the 
semantics of a Tcl command, which is bad!

Is there any reason 'interp aliases' can't return the *current* name of the 
alias, which users can quite happily iterate over. I wouldn't even see this 
as a back-compatibility issue, but as a bug fix.

After all:

proc foo {} {}
rename foo bar
info procs foo
# should obviously not return 'foo'

So, similarly

interp alias {} foo {} implementation
rename foo bar
interp aliases
# should not return foo either



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Comment By: miguel sofer (msofer)
Date: 2003-03-20 21:55

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As noted in
http://groups.google.com/groups?hl=en&safe=off&th=1784032ddc241340%2C4&seekm=8mf2uq%24jkq%241%40bob.news.rcn.net
this behaviour is ancient (since 7.6).

Don's summary of the issue (from the chat):
The issue is the [interp aliases] introspection. It always
returns the original names of the aliases. So even if there
is a [rename], the alias still keeps a connection to its
original name, so it can be reached by folks iterating of
[interp aliases].	
This was a bad choice.  If we need a permanent name for
[interp aliases] to return, we should have a special token
just for that purpose.
For now, the practical advice is "you can't [rename] an alias"

Low priority to signify "not much can be done about it for now".

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Comment By: miguel sofer (msofer)
Date: 2003-03-20 21:26

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Yup, this is weird ... 
It is not a new issue in 8.4 (pheww!), it fails already in 8.3.4

% info patch
8.3.4
% proc foo {} { puts "orig" }
% interp alias {} bar {} foo
bar
% bar
orig
% rename bar bar2
% bar
orig
% bar2
orig
% rename bar {}
can't delete "bar": command doesn't exist
% bar
orig
% bar2
orig
% rename bar2 {}
% bar
invalid command name "bar"
% bar2
invalid command name "bar2"


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Comment By: Don Porter (dgp)
Date: 2003-03-20 21:26

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This is a known issue, and can't
really be corrected unless/until
[interp aliases] is changed to return
a token.  See FR 524140.

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