Practical Programming in Tcl & Tk, Third Edition

The blob Command Example

This section illustrates some standard coding practices with a bigger example. The example is still artificial in that it doesn't actually do very much. However, it illustrates a few more common idioms you should know about when creating Tcl commands.

The blob command creates and manipulates blobs. Each blob has a name and some associated properties. The blob command uses a hash table to keep track of blobs by their name. The hash table is an example of state associated with a command that needs to be cleaned up when the Tcl interpreter is destroyed. The Tcl hash table implementation is nice and general, too, so you may find it helpful in a variety of situations.

You can associate a Tcl script with a blob. When you poke ...