1ensemble(n) [incr Tcl] ensemble(n)
2______________________________________________________________________________
6
8 itcl::ensemble - create or modify a composite command
9
11 itcl::ensemble ensName ?command arg arg...?
12 or
13 ensemble ensName {
14 part partName args body
15 ...
16 ensemble partName {
17 part subPartName args body
18 part subPartName args body
19 ...
20 }
21 }
22______________________________________________________________________________
23
26 The ensemble command is used to create or modify a composite command.
27 See the section WHAT IS AN ENSEMBLE? below for a brief overview of
28 ensembles.
29 If the ensemble command finds an existing ensemble called ensName, it
31 updates that ensemble. Otherwise, it creates an ensemble called
32 ensName. If the ensName is a simple name like "foo", then an ensemble
33 command named "foo" is added to the current namespace context. If a
34 command named "foo" already exists in that context, then it is deleted.
35 If the ensName contains namespace qualifiers like "a::b::foo", then the
36 namespace path is resolved, and the ensemble command is added that
37 namespace context. Parent namespaces like "a" and "b" are created
38 automatically, as needed.
39 If the ensName contains spaces like "a::b::foo bar baz", then addi‐
41 tional words like "bar" and "baz" are treated as sub-ensembles. Sub-
42 ensembles are merely parts within an ensemble; they do not have a Tcl
43 command associated with them. An ensemble like "foo" can have a sub-
44 ensemble called "foo bar", which in turn can have a sub-ensemble called
45 "foo bar baz". In this case, the sub-ensemble "foo bar" must be cre‐
46 ated before the sub-ensemble "foo bar baz" that resides within it.
47 If there are any arguments following ensName, then they are treated as
49 commands, and they are executed to update the ensemble. The following
50 commands are recognized in this context: part and ensemble.
51 The part command defines a new part for the ensemble. Its syntax is
53 identical to the usual proc command, but it defines a part within an
54 ensemble, instead of a Tcl command. If a part called partName already
55 exists within the ensemble, then the part command returns an error.
56 The ensemble command can be nested inside another ensemble command to
58 define a sub-ensemble.
59
62 The usual "info" command is a composite command--the command name info
63 must be followed by a sub-command like body or globals. We will refer
64 to a command like info as an ensemble, and to sub-commands like body or
65 globals as its parts.
66 Ensembles can be nested. For example, the info command has an ensemble
68 info namespace within it. This ensemble has parts like info namespace
69 all and info namespace children.
70 With ensembles, composite commands can be created and extended in an
72 automatic way. Any package can find an existing ensemble and add new
73 parts to it. So extension writers can add their own parts, for exam‐
74 ple, to the info command.
75 The ensemble facility manages all of the part names and keeps track of
77 unique abbreviations. Normally, you can abbreviate info complete to
78 info comp. But if an extension adds the part info complexity, the min‐
79 imum abbreviation for info complete becomes info complet.
80 The ensemble facility not only automates the construction of composite
82 commands, but it automates the error handling as well. If you invoke
83 an ensemble command without specifying a part name, you get an automat‐
84 ically generated error message that summarizes the usage information.
85 For example, when the info command is invoked without any arguments, it
86 produces the following error message:
87 wrong # args: should be one of...
89 info args procname
90 info body procname
91 info cmdcount
92 info commands ?pattern?
93 info complete command
94 info context
95 info default procname arg varname
96 info exists varName
97 info globals ?pattern?
98 info level ?number?
99 info library
100 info locals ?pattern?
101 info namespace option ?arg arg ...?
102 info patchlevel
103 info procs ?pattern?
104 info protection ?-command? ?-variable? name
105 info script
106 info tclversion
107 info vars ?pattern?
108 info which ?-command? ?-variable? ?-namespace? name
109 You can also customize the way an ensemble responds to errors. When an
111 ensemble encounters an unspecified or ambiguous part name, it looks for
112 a part called @error. If it exists, then it is used to handle the
113 error. This part will receive all of the arguments on the command line
114 starting with the offending part name. It can find another way of
115 resolving the command, or generate its own error message.
116
119 We could use an ensemble to clean up the syntax of the various "wait"
120 commands in Tcl/Tk. Instead of using a series of strange commands like
121 this:
122 vwait x
124 tkwait visibility .top
125 tkwait window .
126 we could use commands with a uniform syntax, like this:
128 wait variable x
130 wait visibility .top
131 wait window .
132 The Tcl package could define the following ensemble:
134 itcl::ensemble wait part variable {name} {
136 uplevel vwait $name
137 }
138 The Tk package could add some options to this ensemble, with a command
140 like this:
141 itcl::ensemble wait {
143 part visibility {name} {
144 tkwait visibility $name
145 }
146 part window {name} {
147 tkwait window $name
148 }
149 }
150 Other extensions could add their own parts to the wait command too.
152
155 ensemble, part, info
156itcl 3.0 ensemble(n)