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 03:14:34)

 T213 - Tcl/Tk - Libraries, Packages and Namespaces

Back to a comment on comments

Previous and next or Horse's mouth home

Forward to Recent technical articles

Confession
Fish stocks
Programming in isolation
Recent technical articles
example of Tcl namespaces and packages
a comment on comments
Tcl sandwich - lists in Tcl
Network Camera
Colour for access
Too technical?
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 at 50 posts per page


This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).