Tcl - Newby question about colons

Author

Newby question about colons

pn8830

2007-04-25, 7:07 pm

Hi,

It's probably a very simple question but I could not find answer
mostly because google does nto accept :: as a search pattern :(
Why do some Tcl commands have :: in them (for example md5 hash -
[::md5::md5] ). This must be some sort of naming convention and this
should be for a reason. I would like to know that reason just to
understand things better. Could someone help?

Thanks,
PN.

Bryan Oakley

2007-04-25, 7:07 pm

pn8830 wrote:
> Hi,
>
> It's probably a very simple question but I could not find answer
> mostly because google does nto accept :: as a search pattern :(
> Why do some Tcl commands have :: in them (for example md5 hash -
> [::md5::md5] ). This must be some sort of naming convention and this
> should be for a reason. I would like to know that reason just to
> understand things better. Could someone help?
>
> Thanks,
> PN.
>

:: is a namespace separator. :: by itself refers to the global
namespace. So, if you see ::foo, it means to explicitly run the command
"foo" defined in the global namespace.

This is mostly used if you redefine a core command in a namespace and
want to reference the core command instead of the namespace command. For
example:

namespace eval Foo {
proc set {a b} {
puts "this is set, inside of foo"
}
proc bar {} {
# use the "set" defined in this namespace
set a b
# use the core "set" command
::set a b
}
}
::Foo::bar

More information on namespaces is here:

http://www.tcl.tk/man/tcl8.4/TclCmd/namespace.htm#M20

--
Bryan Oakley
http://www.tclscripting.com

Sponsored Links