1namespace(n) Tcl Built-In Commands namespace(n)
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8 namespace - create and manipulate contexts for commands and variables
9
11 namespace ?subcommand? ?arg ...?
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13
15 The namespace command lets you create, access, and destroy separate
16 contexts for commands and variables. See the section WHAT IS A NAMES‐
17 PACE? below for a brief overview of namespaces. The legal values of
18 subcommand are listed below. Note that you can abbreviate the subcom‐
19 mands.
20 namespace children ?namespace? ?pattern?
22 Returns a list of all child namespaces that belong to the names‐
23 pace namespace. If namespace is not specified, then the chil‐
24 dren are returned for the current namespace. This command
25 returns fully-qualified names, which start with a double colon
26 (::). If the optional pattern is given, then this command
27 returns only the names that match the glob-style pattern. The
28 actual pattern used is determined as follows: a pattern that
29 starts with double colon (::) is used directly, otherwise the
30 namespace namespace (or the fully-qualified name of the current
31 namespace) is prepended onto the pattern.
32 namespace code script
34 Captures the current namespace context for later execution of
35 the script script. It returns a new script in which script has
36 been wrapped in a namespace inscope command. The new script has
37 two important properties. First, it can be evaluated in any
38 namespace and will cause script to be evaluated in the current
39 namespace (the one where the namespace code command was
40 invoked). Second, additional arguments can be appended to the
41 resulting script and they will be passed to script as additional
42 arguments. For example, suppose the command set script [names‐
43 pace code {foo bar}] is invoked in namespace ::a::b. Then eval
44 $script [list x y] can be executed in any namespace (assuming
45 the value of script has been passed in properly) and will have
46 the same effect as the command ::namespace eval ::a::b {foo bar
47 x y}. This command is needed because extensions like Tk nor‐
48 mally execute callback scripts in the global namespace. A
49 scoped command captures a command together with its namespace
50 context in a way that allows it to be executed properly later.
51 See the section SCOPED SCRIPTS for some examples of how this is
52 used to create callback scripts.
53 namespace current
55 Returns the fully-qualified name for the current namespace. The
56 actual name of the global namespace is “” (i.e., an empty
57 string), but this command returns :: for the global namespace as
58 a convenience to programmers.
59 namespace delete ?namespace namespace ...?
61 Each namespace namespace is deleted and all variables, proce‐
62 dures, and child namespaces contained in the namespace are
63 deleted. If a procedure is currently executing inside the
64 namespace, the namespace will be kept alive until the procedure
65 returns; however, the namespace is marked to prevent other code
66 from looking it up by name. If a namespace does not exist, this
67 command returns an error. If no namespace names are given, this
68 command does nothing.
69 namespace ensemble subcommand ?arg ...?
71 Creates and manipulates a command that is formed out of an
72 ensemble of subcommands. See the section ENSEMBLES below for
73 further details.
74 namespace eval namespace arg ?arg ...?
76 Activates a namespace called namespace and evaluates some code
77 in that context. If the namespace does not already exist, it is
78 created. If more than one arg argument is specified, the argu‐
79 ments are concatenated together with a space between each one in
80 the same fashion as the eval command, and the result is evalu‐
81 ated.
82 If namespace has leading namespace qualifiers and any leading
84 namespaces do not exist, they are automatically created.
85 namespace exists namespace
87 Returns 1 if namespace is a valid namespace in the current con‐
88 text, returns 0 otherwise.
89 namespace export ?-clear? ?pattern pattern ...?
91 Specifies which commands are exported from a namespace. The
92 exported commands are those that can be later imported into
93 another namespace using a namespace import command. Both com‐
94 mands defined in a namespace and commands the namespace has pre‐
95 viously imported can be exported by a namespace. The commands
96 do not have to be defined at the time the namespace export com‐
97 mand is executed. Each pattern may contain glob-style special
98 characters, but it may not include any namespace qualifiers.
99 That is, the pattern can only specify commands in the current
100 (exporting) namespace. Each pattern is appended onto the names‐
101 pace's list of export patterns. If the -clear flag is given,
102 the namespace's export pattern list is reset to empty before any
103 pattern arguments are appended. If no patterns are given and
104 the -clear flag is not given, this command returns the names‐
105 pace's current export list.
106 namespace forget ?pattern pattern ...?
108 Removes previously imported commands from a namespace. Each
109 pattern is a simple or qualified name such as x, foo::x or
110 a::b::p*. Qualified names contain double colons (::) and qual‐
111 ify a name with the name of one or more namespaces. Each “qual‐
112 ified pattern” is qualified with the name of an exporting names‐
113 pace and may have glob-style special characters in the command
114 name at the end of the qualified name. Glob characters may not
115 appear in a namespace name. For each “simple pattern” this com‐
116 mand deletes the matching commands of the current namespace that
117 were imported from a different namespace. For “qualified pat‐
118 terns”, this command first finds the matching exported commands.
119 It then checks whether any of those commands were previously
120 imported by the current namespace. If so, this command deletes
121 the corresponding imported commands. In effect, this un-does
122 the action of a namespace import command.
123 namespace import ?-force? ?pattern pattern ...?
125 Imports commands into a namespace, or queries the set of
126 imported commands in a namespace. When no arguments are
127 present, namespace import returns the list of commands in the
128 current namespace that have been imported from other namespaces.
129 The commands in the returned list are in the format of simple
130 names, with no namespace qualifiers at all. This format is
131 suitable for composition with namespace forget (see EXAMPLES
132 below).
133 When pattern arguments are present, each pattern is a qualified
135 name like foo::x or a::p*. That is, it includes the name of an
136 exporting namespace and may have glob-style special characters
137 in the command name at the end of the qualified name. Glob
138 characters may not appear in a namespace name. When the names‐
139 pace name is not fully qualified (i.e., does not start with a
140 namespace separator) it is resolved as a namespace name in the
141 way described in the NAME RESOLUTION section; it is an error if
142 no namespace with that name can be found.
143 All the commands that match a pattern string and which are cur‐
145 rently exported from their namespace are added to the current
146 namespace. This is done by creating a new command in the cur‐
147 rent namespace that points to the exported command in its origi‐
148 nal namespace; when the new imported command is called, it
149 invokes the exported command. This command normally returns an
150 error if an imported command conflicts with an existing command.
151 However, if the -force option is given, imported commands will
152 silently replace existing commands. The namespace import com‐
153 mand has snapshot semantics: that is, only requested commands
154 that are currently defined in the exporting namespace are
155 imported. In other words, you can import only the commands that
156 are in a namespace at the time when the namespace import command
157 is executed. If another command is defined and exported in this
158 namespace later on, it will not be imported.
159 namespace inscope namespace script ?arg ...?
161 Executes a script in the context of the specified namespace.
162 This command is not expected to be used directly by programmers;
163 calls to it are generated implicitly when applications use
164 namespace code commands to create callback scripts that the
165 applications then register with, e.g., Tk widgets. The names‐
166 pace inscope command is much like the namespace eval command
167 except that the namespace must already exist, and namespace
168 inscope appends additional args as proper list elements.
169 namespace inscope ::foo $script $x $y $z
171 is equivalent to
173 namespace eval ::foo [concat $script [list $x $y $z]]
175 thus additional arguments will not undergo a second round of
177 substitution, as is the case with namespace eval.
178 namespace origin command
180 Returns the fully-qualified name of the original command to
181 which the imported command command refers. When a command is
182 imported into a namespace, a new command is created in that
183 namespace that points to the actual command in the exporting
184 namespace. If a command is imported into a sequence of names‐
185 paces a, b,...,n where each successive namespace just imports
186 the command from the previous namespace, this command returns
187 the fully-qualified name of the original command in the first
188 namespace, a. If command does not refer to an imported command,
189 the command's own fully-qualified name is returned.
190 namespace parent ?namespace?
192 Returns the fully-qualified name of the parent namespace for
193 namespace namespace. If namespace is not specified, the fully-
194 qualified name of the current namespace's parent is returned.
195 namespace path ?namespaceList?
197 Returns the command resolution path of the current namespace. If
198 namespaceList is specified as a list of named namespaces, the
199 current namespace's command resolution path is set to those
200 namespaces and returns the empty list. The default command reso‐
201 lution path is always empty. See the section NAME RESOLUTION
202 below for an explanation of the rules regarding name resolution.
203 namespace qualifiers string
205 Returns any leading namespace qualifiers for string. Qualifiers
206 are namespace names separated by double colons (::). For the
207 string ::foo::bar::x, this command returns ::foo::bar, and for
208 :: it returns an empty string. This command is the complement
209 of the namespace tail command. Note that it does not check
210 whether the namespace names are, in fact, the names of currently
211 defined namespaces.
212 namespace tail string
214 Returns the simple name at the end of a qualified string. Qual‐
215 ifiers are namespace names separated by double colons (::). For
216 the string ::foo::bar::x, this command returns x, and for :: it
217 returns an empty string. This command is the complement of the
218 namespace qualifiers command. It does not check whether the
219 namespace names are, in fact, the names of currently defined
220 namespaces.
221 namespace upvar namespace ?otherVar myVar ...?
223 This command arranges for zero or more local variables in the
224 current procedure to refer to variables in namespace. The names‐
225 pace name is resolved as described in section NAME RESOLUTION.
226 The command namespace upvar $ns a b has the same behaviour as
227 upvar 0 ${ns}::a b, with the sole exception of the resolution
228 rules used for qualified namespace or variable names. namespace
229 upvar returns an empty string.
230 namespace unknown ?script?
232 Sets or returns the unknown command handler for the current
233 namespace. The handler is invoked when a command called from
234 within the namespace cannot be found in the current namespace,
235 the namespace's path nor in the global namespace. The script
236 argument, if given, should be a well formed list representing a
237 command name and optional arguments. When the handler is
238 invoked, the full invocation line will be appended to the script
239 and the result evaluated in the context of the namespace. The
240 default handler for all namespaces is ::unknown. If no argument
241 is given, it returns the handler for the current namespace.
242 namespace which ?-command? ?-variable? name
244 Looks up name as either a command or variable and returns its
245 fully-qualified name. For example, if name does not exist in
246 the current namespace but does exist in the global namespace,
247 this command returns a fully-qualified name in the global names‐
248 pace. If the command or variable does not exist, this command
249 returns an empty string. If the variable has been created but
250 not defined, such as with the variable command or through a
251 trace on the variable, this command will return the fully-quali‐
252 fied name of the variable. If no flag is given, name is treated
253 as a command name. See the section NAME RESOLUTION below for an
254 explanation of the rules regarding name resolution.
255
257 A namespace is a collection of commands and variables. It encapsulates
258 the commands and variables to ensure that they will not interfere with
259 the commands and variables of other namespaces. Tcl has always had one
260 such collection, which we refer to as the global namespace. The global
261 namespace holds all global variables and commands. The namespace eval
262 command lets you create new namespaces. For example,
263 namespace eval Counter {
265 namespace export bump
266 variable num 0
267 proc bump {} {
269 variable num
270 incr num
271 }
272 }
273 creates a new namespace containing the variable num and the procedure
275 bump. The commands and variables in this namespace are separate from
276 other commands and variables in the same program. If there is a com‐
277 mand named bump in the global namespace, for example, it will be dif‐
278 ferent from the command bump in the Counter namespace.
279 Namespace variables resemble global variables in Tcl. They exist out‐
281 side of the procedures in a namespace but can be accessed in a proce‐
282 dure via the variable command, as shown in the example above.
283 Namespaces are dynamic. You can add and delete commands and variables
285 at any time, so you can build up the contents of a namespace over time
286 using a series of namespace eval commands. For example, the following
287 series of commands has the same effect as the namespace definition
288 shown above:
289 namespace eval Counter {
291 variable num 0
292 proc bump {} {
293 variable num
294 return [incr num]
295 }
296 }
297 namespace eval Counter {
298 proc test {args} {
299 return $args
300 }
301 }
302 namespace eval Counter {
303 rename test ""
304 }
305 Note that the test procedure is added to the Counter namespace, and
307 later removed via the rename command.
308 Namespaces can have other namespaces within them, so they nest hierar‐
310 chically. A nested namespace is encapsulated inside its parent names‐
311 pace and can not interfere with other namespaces.
312
314 Each namespace has a textual name such as history or ::safe::interp.
315 Since namespaces may nest, qualified names are used to refer to com‐
316 mands, variables, and child namespaces contained inside namespaces.
317 Qualified names are similar to the hierarchical path names for Unix
318 files or Tk widgets, except that :: is used as the separator instead of
319 / or .. The topmost or global namespace has the name “” (i.e., an
320 empty string), although :: is a synonym. As an example, the name
321 ::safe::interp::create refers to the command create in the namespace
322 interp that is a child of namespace ::safe, which in turn is a child of
323 the global namespace, ::.
324 If you want to access commands and variables from another namespace,
326 you must use some extra syntax. Names must be qualified by the names‐
327 pace that contains them. From the global namespace, we might access
328 the Counter procedures like this:
329 Counter::bump 5
331 Counter::Reset
332 We could access the current count like this:
334 puts "count = $Counter::num"
336 When one namespace contains another, you may need more than one quali‐
338 fier to reach its elements. If we had a namespace Foo that contained
339 the namespace Counter, you could invoke its bump procedure from the
340 global namespace like this:
341 Foo::Counter::bump 3
343 You can also use qualified names when you create and rename commands.
345 For example, you could add a procedure to the Foo namespace like this:
346 proc Foo::Test {args} {return $args}
348 And you could move the same procedure to another namespace like this:
350 rename Foo::Test Bar::Test
352 There are a few remaining points about qualified names that we should
354 cover. Namespaces have nonempty names except for the global namespace.
355 :: is disallowed in simple command, variable, and namespace names
356 except as a namespace separator. Extra colons in any separator part of
357 a qualified name are ignored; i.e. two or more colons are treated as a
358 namespace separator. A trailing :: in a qualified variable or command
359 name refers to the variable or command named {}. However, a trailing
360 :: in a qualified namespace name is ignored.
361
363 In general, all Tcl commands that take variable and command names sup‐
364 port qualified names. This means you can give qualified names to such
365 commands as set, proc, rename, and interp alias. If you provide a
366 fully-qualified name that starts with a ::, there is no question about
367 what command, variable, or namespace you mean. However, if the name
368 does not start with a :: (i.e., is relative), Tcl follows basic rules
369 for looking it up:
370 · Variable names are always resolved by looking first in the cur‐
372 rent namespace, and then in the global namespace.
373 · Command names are always resolved by looking in the current
375 namespace first. If not found there, they are searched for in
376 every namespace on the current namespace's command path (which
377 is empty by default). If not found there, command names are
378 looked up in the global namespace (or, failing that, are pro‐
379 cessed by the appropriate namespace unknown handler.)
380 · Namespace names are always resolved by looking in only the cur‐
382 rent namespace.
383 In the following example,
385 set traceLevel 0
387 namespace eval Debug {
388 printTrace $traceLevel
389 }
390 Tcl looks for traceLevel in the namespace Debug and then in the global
392 namespace. It looks up the command printTrace in the same way. If a
393 variable or command name is not found in either context, the name is
394 undefined. To make this point absolutely clear, consider the following
395 example:
396 set traceLevel 0
398 namespace eval Foo {
399 variable traceLevel 3
400 namespace eval Debug {
402 printTrace $traceLevel
403 }
404 }
405 Here Tcl looks for traceLevel first in the namespace Foo::Debug. Since
407 it is not found there, Tcl then looks for it in the global namespace.
408 The variable Foo::traceLevel is completely ignored during the name res‐
409 olution process.
410 You can use the namespace which command to clear up any question about
412 name resolution. For example, the command:
413 namespace eval Foo::Debug {namespace which -variable traceLevel}
415 returns ::traceLevel. On the other hand, the command,
417 namespace eval Foo {namespace which -variable traceLevel}
419 returns ::Foo::traceLevel.
421 As mentioned above, namespace names are looked up differently than the
423 names of variables and commands. Namespace names are always resolved
424 in the current namespace. This means, for example, that a namespace
425 eval command that creates a new namespace always creates a child of the
426 current namespace unless the new namespace name begins with ::.
427 Tcl has no access control to limit what variables, commands, or names‐
429 paces you can reference. If you provide a qualified name that resolves
430 to an element by the name resolution rule above, you can access the
431 element.
432 You can access a namespace variable from a procedure in the same names‐
434 pace by using the variable command. Much like the global command, this
435 creates a local link to the namespace variable. If necessary, it also
436 creates the variable in the current namespace and initializes it. Note
437 that the global command only creates links to variables in the global
438 namespace. It is not necessary to use a variable command if you always
439 refer to the namespace variable using an appropriate qualified name.
440
442 Namespaces are often used to represent libraries. Some library com‐
443 mands are used so frequently that it is a nuisance to type their quali‐
444 fied names. For example, suppose that all of the commands in a package
445 like BLT are contained in a namespace called Blt. Then you might
446 access these commands like this:
447 Blt::graph .g -background red
449 Blt::table . .g 0,0
450 If you use the graph and table commands frequently, you may want to
452 access them without the Blt:: prefix. You can do this by importing the
453 commands into the current namespace, like this:
454 namespace import Blt::*
456 This adds all exported commands from the Blt namespace into the current
458 namespace context, so you can write code like this:
459 graph .g -background red
461 table . .g 0,0
462 The namespace import command only imports commands from a namespace
464 that that namespace exported with a namespace export command.
465 Importing every command from a namespace is generally a bad idea since
467 you do not know what you will get. It is better to import just the
468 specific commands you need. For example, the command
469 namespace import Blt::graph Blt::table
471 imports only the graph and table commands into the current context.
473 If you try to import a command that already exists, you will get an
475 error. This prevents you from importing the same command from two dif‐
476 ferent packages. But from time to time (perhaps when debugging), you
477 may want to get around this restriction. You may want to reissue the
478 namespace import command to pick up new commands that have appeared in
479 a namespace. In that case, you can use the -force option, and existing
480 commands will be silently overwritten:
481 namespace import -force Blt::graph Blt::table
483 If for some reason, you want to stop using the imported commands, you
485 can remove them with a namespace forget command, like this:
486 namespace forget Blt::*
488 This searches the current namespace for any commands imported from Blt.
490 If it finds any, it removes them. Otherwise, it does nothing. After
491 this, the Blt commands must be accessed with the Blt:: prefix.
492 When you delete a command from the exporting namespace like this:
494 rename Blt::graph ""
496 the command is automatically removed from all namespaces that import
498 it.
499
501 You can export commands from a namespace like this:
502 namespace eval Counter {
504 namespace export bump reset
505 variable Num 0
506 variable Max 100
507 proc bump {{by 1}} {
509 variable Num
510 incr Num $by
511 Check
512 return $Num
513 }
514 proc reset {} {
515 variable Num
516 set Num 0
517 }
518 proc Check {} {
519 variable Num
520 variable Max
521 if {$Num > $Max} {
522 error "too high!"
523 }
524 }
525 }
526 The procedures bump and reset are exported, so they are included when
528 you import from the Counter namespace, like this:
529 namespace import Counter::*
531 However, the Check procedure is not exported, so it is ignored by the
533 import operation.
534 The namespace import command only imports commands that were declared
536 as exported by their namespace. The namespace export command specifies
537 what commands may be imported by other namespaces. If a namespace
538 import command specifies a command that is not exported, the command is
539 not imported.
540
542 The namespace code command is the means by which a script may be pack‐
543 aged for evaluation in a namespace other than the one in which it was
544 created. It is used most often to create event handlers, Tk bindings,
545 and traces for evaluation in the global context. For instance, the
546 following code indicates how to direct a variable trace callback into
547 the current namespace:
548 namespace eval a {
550 variable b
551 proc theTraceCallback { n1 n2 op } {
552 upvar 1 $n1 var
553 puts "the value of $n1 has changed to $var"
554 return
555 }
556 trace add variable b write [namespace code theTraceCallback]
557 }
558 set a::b c
559 When executed, it prints the message:
561 the value of a::b has changed to c
563
565 The namespace ensemble is used to create and manipulate ensemble com‐
566 mands, which are commands formed by grouping subcommands together. The
567 commands typically come from the current namespace when the ensemble
568 was created, though this is configurable. Note that there may be any
569 number of ensembles associated with any namespace (including none,
570 which is true of all namespaces by default), though all the ensembles
571 associated with a namespace are deleted when that namespace is deleted.
572 The link between an ensemble command and its namespace is maintained
573 however the ensemble is renamed.
574 Three subcommands of the namespace ensemble command are defined:
576 namespace ensemble create ?option value ...?
578 Creates a new ensemble command linked to the current namespace,
579 returning the fully qualified name of the command created. The
580 arguments to namespace ensemble create allow the configuration
581 of the command as if with the namespace ensemble configure com‐
582 mand. If not overridden with the -command option, this command
583 creates an ensemble with exactly the same name as the linked
584 namespace. See the section ENSEMBLE OPTIONS below for a full
585 list of options supported and their effects.
586 namespace ensemble configure command ?option? ?value ...?
588 Retrieves the value of an option associated with the ensemble
589 command named command, or updates some options associated with
590 that ensemble command. See the section ENSEMBLE OPTIONS below
591 for a full list of options supported and their effects.
592 namespace ensemble exists command
594 Returns a boolean value that describes whether the command com‐
595 mand exists and is an ensemble command. This command only ever
596 returns an error if the number of arguments to the command is
597 wrong.
598 When called, an ensemble command takes its first argument and looks it
600 up (according to the rules described below) to discover a list of words
601 to replace the ensemble command and subcommand with. The resulting
602 list of words is then evaluated (with no further substitutions) as if
603 that was what was typed originally (i.e. by passing the list of words
604 through Tcl_EvalObjv) and returning the result of the command. Note
605 that it is legal to make the target of an ensemble rewrite be another
606 (or even the same) ensemble command. The ensemble command will not be
607 visible through the use of the uplevel or info level commands.
608 ENSEMBLE OPTIONS
610 The following options, supported by the namespace ensemble create and
611 namespace ensemble configure commands, control how an ensemble command
612 behaves:
613 -map When non-empty, this option supplies a dictionary that provides
615 a mapping from subcommand names to a list of prefix words to
616 substitute in place of the ensemble command and subcommand words
617 (in a manner similar to an alias created with interp alias; the
618 words are not reparsed after substitution); if the first word of
619 any target is not fully qualified when set, it is assumed to be
620 relative to the current namespace and changed to be exactly that
621 (that is, it is always fully qualified when read). When this
622 option is empty, the mapping will be from the local name of the
623 subcommand to its fully-qualified name. Note that when this
624 option is non-empty and the -subcommands option is empty, the
625 ensemble subcommand names will be exactly those words that have
626 mappings in the dictionary.
627 -parameters
629 This option gives a list of named arguments (the names being │
630 used during generation of error messages) that are passed by the │
631 caller of the ensemble between the name of the ensemble and the │
632 subcommand argument. By default, it is the empty list.
633 -prefixes
635 This option (which is enabled by default) controls whether the
636 ensemble command recognizes unambiguous prefixes of its subcom‐
637 mands. When turned off, the ensemble command requires exact
638 matching of subcommand names.
639 -subcommands
641 When non-empty, this option lists exactly what subcommands are
642 in the ensemble. The mapping for each of those commands will be
643 either whatever is defined in the -map option, or to the command
644 with the same name in the namespace linked to the ensemble. If
645 this option is empty, the subcommands of the namespace will
646 either be the keys of the dictionary listed in the -map option
647 or the exported commands of the linked namespace at the time of
648 the invocation of the ensemble command.
649 -unknown
651 When non-empty, this option provides a partial command (to which
652 all the words that are arguments to the ensemble command,
653 including the fully-qualified name of the ensemble, are
654 appended) to handle the case where an ensemble subcommand is not
655 recognized and would otherwise generate an error. When empty
656 (the default) an error (in the style of Tcl_GetIndexFromObj) is
657 generated whenever the ensemble is unable to determine how to
658 implement a particular subcommand. See UNKNOWN HANDLER BEHAV‐
659 IOUR for more details.
660 The following extra option is allowed by namespace ensemble create:
662 -command
664 This write-only option allows the name of the ensemble created
665 by namespace ensemble create to be anything in any existing
666 namespace. The default value for this option is the fully-qual‐
667 ified name of the namespace in which the namespace ensemble cre‐
668 ate command is invoked.
669 The following extra option is allowed by namespace ensemble configure:
671 -namespace
673 This read-only option allows the retrieval of the fully-quali‐
674 fied name of the namespace which the ensemble was created
675 within.
676 UNKNOWN HANDLER BEHAVIOUR
678 If an unknown handler is specified for an ensemble, that handler is
679 called when the ensemble command would otherwise return an error due to
680 it being unable to decide which subcommand to invoke. The exact condi‐
681 tions under which that occurs are controlled by the -subcommands, -map
682 and -prefixes options as described above.
683 To execute the unknown handler, the ensemble mechanism takes the speci‐
685 fied -unknown option and appends each argument of the attempted ensem‐
686 ble command invocation (including the ensemble command itself,
687 expressed as a fully qualified name). It invokes the resulting command
688 in the scope of the attempted call. If the execution of the unknown
689 handler terminates normally, the ensemble engine reparses the subcom‐
690 mand (as described below) and tries to dispatch it again, which is
691 ideal for when the ensemble's configuration has been updated by the
692 unknown subcommand handler. Any other kind of termination of the
693 unknown handler is treated as an error.
694 The result of the unknown handler is expected to be a list (it is an
696 error if it is not). If the list is an empty list, the ensemble command
697 attempts to look up the original subcommand again and, if it is not
698 found this time, an error will be generated just as if the -unknown
699 handler was not there (i.e. for any particular invocation of an ensem‐
700 ble, its unknown handler will be called at most once.) This makes it
701 easy for the unknown handler to update the ensemble or its backing
702 namespace so as to provide an implementation of the desired subcommand
703 and reparse.
704 When the result is a non-empty list, the words of that list are used to
706 replace the ensemble command and subcommand, just as if they had been
707 looked up in the -map. It is up to the unknown handler to supply all
708 namespace qualifiers if the implementing subcommand is not in the
709 namespace of the caller of the ensemble command. Also note that when
710 ensemble commands are chained (e.g. if you make one of the commands
711 that implement an ensemble subcommand into an ensemble, in a manner
712 similar to the text widget's tag and mark subcommands) then the rewrite
713 happens in the context of the caller of the outermost ensemble. That is
714 to say that ensembles do not in themselves place any namespace contexts
715 on the Tcl call stack.
716 Where an empty -unknown handler is given (the default), the ensemble
718 command will generate an error message based on the list of commands
719 that the ensemble has defined (formatted similarly to the error message
720 from Tcl_GetIndexFromObj). This is the error that will be thrown when
721 the subcommand is still not recognized during reparsing. It is also an
722 error for an -unknown handler to delete its namespace.
723
725 Create a namespace containing a variable and an exported command:
726 namespace eval foo {
728 variable bar 0
729 proc grill {} {
730 variable bar
731 puts "called [incr bar] times"
732 }
733 namespace export grill
734 }
735 Call the command defined in the previous example in various ways.
737 # Direct call
739 ::foo::grill
740 # Use the command resolution path to find the name
742 namespace eval boo {
743 namespace path ::foo
744 grill
745 }
746 # Import into current namespace, then call local alias
748 namespace import foo::grill
749 grill
750 # Create two ensembles, one with the default name and one with a
752 # specified name. Then call through the ensembles.
753 namespace eval foo {
754 namespace ensemble create
755 namespace ensemble create -command ::foobar
756 }
757 foo grill
758 foobar grill
759 Look up where the command imported in the previous example came from:
761 puts "grill came from [namespace origin grill]"
763 Remove all imported commands from the current namespace:
765 namespace forget {*}[namespace import]
767 Create an ensemble for simple working with numbers, using the -parame‐ │
769 ters option to allow the operator to be put between the first and sec‐ │
770 ond arguments. │
771 namespace eval do { │
773 namespace export * │
774 namespace ensemble create -parameters x │
775 proc plus {x y} {expr { $x + $y }} │
776 proc minus {x y} {expr { $x - $y }} │
777 } │
778 # In use, the ensemble works like this: │
780 puts [do 1 plus [do 9 minus 7]] │
781
783 interp(n), upvar(n), variable(n)
784
786 command, ensemble, exported, internal, variable
787Tcl 8.5 namespace(n)