Re: [TCLCORE] TIP #349: New "-cargo" option for every Tk widget

[Damon C. <da...@tc...>]

> Why an option, rather than a common command?
>
> It strikes me that an option is rather limited -- give it about 2  
> months
> and we will see reusable bits of code on the wiki that do cool things
> (like tooltips) using -cargo, and suddenly its not really available  
> for
> "the script author" because (s)he is trying to juggle the 5 cool
> extensions that all want to use it.  Only then (too late) does someone
> suggest a protocol for using -cargo (e.g. make it a dict), but there  
> are
> already incompatible uses around.
>
> A "cargo" subcommand that is set up as a key/value mechanism would
> surely be a more generic solution?
>
> e.g.
> button .b
> .b cargo ;# lists cargo keys
> .b cargo key ;# returns the value for "key"
> .b cargo key val ;# sets the value for "key"
>
> This specific interface doesn't deal with deleting cargo values; one
> could assume that the value {} is effectively a delete; one could also
> specify whether ".b cargo key" returns empty or throws an error if key
> does not exist.

I would go one further and say why add a "cargo" method to every  
widget when you can just add a cargo command to attach data to a  
widget?  I argued this same point in the referenced thread, and no one  
listened.  By the way, I prefer clientdata or something like that.

clientdata .b "foo"
clientdata .e [dict create foo bar]

Whatever.  If you REALLY wanted to implement this in C, you could, but  
it's quite easy in Tcl.  I would just use a simple command trace on  
the deletion of the widget.  Binding to <Destroy>, as some in the  
original thread had suggested, has the side-effect of being easy to  
wipe out by the developer if they choose to bind <Destroy> themselves.

D