example of Tcl namespaces and packages

For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Packages in Tcl allow you to define a file of code that's going to be loaded as required at run time. Namespaces allow you to define a new set of variable and proc names that doesn't conflict with the variable and proc names in your main program - rather like giving all the variable and procs in part of your code a surname.

Although packages and namespaces are different facilities and technically not linked in any way, in practise they're often used together. I've often been asked for a simple example showing the mechanism of packages and namespaces working together ...

Here's a main program:

lappend auto_path /home/trainee/ltcl/bowbells
package require amerifruit 1.0
puts [usa::grapefruit]

Here's the file that defines the amerifruit package - it happens to be called florida.tcl in a directory called bowbells:

package provide amerifruit 1.0
namespace eval usa {
proc grapefruit {} {
puts "Big water melons"
}
}

The file bowbells/pkgIndex.tcl provides an index that links the amerifruit package to the florida.tcl file:

package ifneeded amerifruit 1.0 [list source [file join $dir florida.tcl]]
package ifneeded fruit 1.0 [list source [file join $dir clements.tcl]]

If you're worried about the syntax of this, don't be; it was genarated by the command
pkg_mkIndex . *.tcl
run in interactive mode in the bowbells directory

For further details and examples, see our training module on the subject
(written 2004-12-10, updated 2006-06-05)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

T213 - Tcl/Tk - Libraries, Packages and Namespaces
  [1339] Packages and Namespaces are like Suitcases and Aircraft - (2007-09-09)
  [1529] Tcl - learning how to use namespaces, packages and libraries together - (2008-02-02)
  [2476] Tcl - uplevel to run code at calling level - (2009-10-24)
  [3066] Separating groups of variables into namespaces - (2010-11-24)
  [3417] What is a namespace and why do we need them? - (2011-09-03)
  [3418] Tcl packages, pkg_mkIndex, pkgIndex.tcl -what are they and why use them. - (2011-09-03)
  [4522] Loading packages in your Tcl program - (2015-10-09)

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