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namespace(n)                 Tcl Built-In Commands                namespace(n)

______________________________________________________________________________


NAME

       namespace - create and manipulate contexts for commands and variables


SYNOPSIS

       namespace subcommand ?arg ...?
______________________________________________________________________________


DESCRIPTION

       The namespace command lets you create, access, and destroy separate
       contexts for commands and variables.  See the section WHAT IS A
       NAMESPACE? below for a brief overview of namespaces.  The legal values
       of subcommand are listed below.  Note that you can abbreviate the
       subcommands.

       namespace children ?namespace? ?pattern?
              Returns a list of all child namespaces that belong to the
              namespace namespace.  If namespace is not specified, then the
              children are returned for the current namespace.  This command
              returns fully-qualified names, which start with a double colon
              (::).  If the optional pattern is given, then this command
              returns only the names that match the glob-style pattern.  The
              actual pattern used is determined as follows: a pattern that
              starts with double colon (::) is used directly, otherwise the
              namespace namespace (or the fully-qualified name of the current
              namespace) is prepended onto the pattern.

       namespace code script
              Captures the current namespace context for later execution of
              the script script.  It returns a new script in which script has
              been wrapped in a namespace inscope command.  The new script has
              two important properties.  First, it can be evaluated in any
              namespace and will cause script to be evaluated in the current
              namespace (the one where the namespace code command was
              invoked).  Second, additional arguments can be appended to the
              resulting script and they will be passed to script as additional
              arguments.  For example, suppose the command set script
              [namespace code {foo bar}] is invoked in namespace ::a::b.  Then
              eval $script [list x y] can be executed in any namespace
              (assuming the value of script has been passed in properly) and
              will have the same effect as the command ::namespace eval ::a::b
              {foo bar x y}.  This command is needed because extensions like
              Tk normally execute callback scripts in the global namespace.  A
              scoped command captures a command together with its namespace
              context in a way that allows it to be executed properly later.
              See the section SCOPED SCRIPTS for some examples of how this is
              used to create callback scripts.

       namespace current
              Returns the fully-qualified name for the current namespace.  The
              actual name of the global namespace is "" (i.e., an empty
              string), but this command returns :: for the global namespace as
              a convenience to programmers.

       namespace delete ?namespace namespace ...?
              Each namespace namespace is deleted and all variables,
              procedures, and child namespaces contained in the namespace are
              deleted.  If a procedure is currently executing inside the
              namespace, the namespace will be kept alive until the procedure
              returns; however, the namespace is marked to prevent other code
              from looking it up by name.  If a namespace does not exist, this
              command returns an error.  If no namespace names are given, this
              command does nothing.

       namespace ensemble subcommand ?arg ...?
              Creates and manipulates a command that is formed out of an
              ensemble of subcommands.  See the section ENSEMBLES below for
              further details.

       namespace eval namespace arg ?arg ...?
              Activates a namespace called namespace and evaluates some code
              in that context.  If the namespace does not already exist, it is
              created.  If more than one arg argument is specified, the
              arguments are concatenated together with a space between each
              one in the same fashion as the eval command, and the result is
              evaluated.

              If namespace has leading namespace qualifiers and any leading
              namespaces do not exist, they are automatically created.

       namespace exists namespace
              Returns 1 if namespace is a valid namespace in the current
              context, returns 0 otherwise.

       namespace export ?-clear? ?pattern pattern ...?
              Specifies which commands are exported from a namespace.  The
              exported commands are those that can be later imported into
              another namespace using a namespace import command.  Both
              commands defined in a namespace and commands the namespace has
              previously imported can be exported by a namespace.  The
              commands do not have to be defined at the time the namespace
              export command is executed.  Each pattern may contain glob-style
              special characters, but it may not include any namespace
              qualifiers.  That is, the pattern can only specify commands in
              the current (exporting) namespace.  Each pattern is appended
              onto the namespace's list of export patterns.  If the -clear
              flag is given, the namespace's export pattern list is reset to
              empty before any pattern arguments are appended.  If no patterns
              are given and the -clear flag is not given, this command returns
              the namespace's current export list.

       namespace forget ?pattern pattern ...?
              Removes previously imported commands from a namespace.  Each
              pattern is a simple or qualified name such as x, foo::x or
              a::b::p*.  Qualified names contain double colons (::) and
              qualify a name with the name of one or more namespaces.  Each
              "qualified pattern" is qualified with the name of an exporting
              namespace and may have glob-style special characters in the
              command name at the end of the qualified name.  Glob characters
              may not appear in a namespace name.  For each "simple pattern"
              this command deletes the matching commands of the current
              namespace that were imported from a different namespace.  For
              "qualified patterns", this command first finds the matching
              exported commands.  It then checks whether any of those commands
              were previously imported by the current namespace.  If so, this
              command deletes the corresponding imported commands.  In effect,
              this undoes the action of a namespace import command.

       namespace import ?-force? ?pattern pattern ...?
              Imports commands into a namespace, or queries the set of
              imported commands in a namespace.  When no arguments are
              present, namespace import returns the list of commands in the
              current namespace that have been imported from other namespaces.
              The commands in the returned list are in the format of simple
              names, with no namespace qualifiers at all.  This format is
              suitable for composition with namespace forget (see EXAMPLES
              below).

              When pattern arguments are present, each pattern is a qualified
              name like foo::x or a::p*.  That is, it includes the name of an
              exporting namespace and may have glob-style special characters
              in the command name at the end of the qualified name.  Glob
              characters may not appear in a namespace name.  When the
              namespace name is not fully qualified (i.e., does not start with
              a namespace separator) it is resolved as a namespace name in the
              way described in the NAME RESOLUTION section; it is an error if
              no namespace with that name can be found.

              All the commands that match a pattern string and which are
              currently exported from their namespace are added to the current
              namespace.  This is done by creating a new command in the
              current namespace that points to the exported command in its
              original namespace; when the new imported command is called, it
              invokes the exported command.  This command normally returns an
              error if an imported command conflicts with an existing command.
              However, if the -force option is given, imported commands will
              silently replace existing commands.  The namespace import
              command has snapshot semantics: that is, only requested commands
              that are currently defined in the exporting namespace are
              imported.  In other words, you can import only the commands that
              are in a namespace at the time when the namespace import command
              is executed.  If another command is defined and exported in this
              namespace later on, it will not be imported.

       namespace inscope namespace script ?arg ...?
              Executes a script in the context of the specified namespace.
              This command is not expected to be used directly by programmers;
              calls to it are generated implicitly when applications use
              namespace code commands to create callback scripts that the
              applications then register with, e.g., Tk widgets.  The
              namespace inscope command is much like the namespace eval
              command except that the namespace must already exist, and
              namespace inscope appends additional args as proper list
              elements.

                     namespace inscope ::foo $script $x $y $z

              is equivalent to

                     namespace eval ::foo [concat $script [list $x $y $z]]

              thus additional arguments will not undergo a second round of
              substitution, as is the case with namespace eval.

       namespace origin command
              Returns the fully-qualified name of the original command to
              which the imported command command refers.  When a command is
              imported into a namespace, a new command is created in that
              namespace that points to the actual command in the exporting
              namespace.  If a command is imported into a sequence of
              namespaces a, b,...,n where each successive namespace just
              imports the command from the previous namespace, this command
              returns the fully-qualified name of the original command in the
              first namespace, a.  If command does not refer to an imported
              command, the command's own fully-qualified name is returned.

       namespace parent ?namespace?
              Returns the fully-qualified name of the parent namespace for
              namespace namespace.  If namespace is not specified, the fully-
              qualified name of the current namespace's parent is returned.

       namespace path ?namespaceList?
              Returns the command resolution path of the current namespace. If
              namespaceList is specified as a list of named namespaces, the
              current namespace's command resolution path is set to those
              namespaces and returns the empty list. The default command
              resolution path is always empty. See the section NAME RESOLUTION
              below for an explanation of the rules regarding name resolution.

       namespace qualifiers string
              Returns any leading namespace qualifiers for string.  Qualifiers
              are namespace names separated by double colons (::).  For the
              string ::foo::bar::x, this command returns ::foo::bar, and for
              :: it returns an empty string.  This command is the complement
              of the namespace tail command.  Note that it does not check
              whether the namespace names are, in fact, the names of currently
              defined namespaces.

       namespace tail string
              Returns the simple name at the end of a qualified string.
              Qualifiers are namespace names separated by double colons (::).
              For the string ::foo::bar::x, this command returns x, and for ::
              it returns an empty string.  This command is the complement of
              the namespace qualifiers command.  It does not check whether the
              namespace names are, in fact, the names of currently defined
              namespaces.

       namespace upvar namespace ?otherVar myVar ...?
              This command arranges for zero or more local variables in the
              current procedure to refer to variables in namespace. The
              namespace name is resolved as described in section NAME
              RESOLUTION.  The command namespace upvar $ns a b has the same
              behaviour as upvar 0 ${ns}::a b, with the sole exception of the
              resolution rules used for qualified namespace or variable names.
              namespace upvar returns an empty string.

       namespace unknown ?script?
              Sets or returns the unknown command handler for the current
              namespace.  The handler is invoked when a command called from
              within the namespace cannot be found in the current namespace,
              the namespace's path nor in the global namespace.  The script
              argument, if given, should be a well formed list representing a
              command name and optional arguments. When the handler is
              invoked, the full invocation line will be appended to the script
              and the result evaluated in the context of the namespace. The
              default handler for all namespaces is ::unknown. If no argument
              is given, it returns the handler for the current namespace.

       namespace which ?-command? ?-variable? name
              Looks up name as either a command or variable and returns its
              fully-qualified name.  For example, if name does not exist in
              the current namespace but does exist in the global namespace,
              this command returns a fully-qualified name in the global
              namespace.  If the command or variable does not exist, this
              command returns an empty string.  If the variable has been
              created but not defined, such as with the variable command or
              through a trace on the variable, this command will return the
              fully-qualified name of the variable.  If no flag is given, name
              is treated as a command name.  See the section NAME RESOLUTION
              below for an explanation of the rules regarding name resolution.


WHAT IS A NAMESPACE?

       A namespace is a collection of commands and variables.  It encapsulates
       the commands and variables to ensure that they will not interfere with
       the commands and variables of other namespaces.  Tcl has always had one
       such collection, which we refer to as the global namespace.  The global
       namespace holds all global variables and commands.  The namespace eval
       command lets you create new namespaces.  For example,

              namespace eval Counter {
                  namespace export bump
                  variable num 0

                  proc bump {} {
                      variable num
                      incr num
                  }
              }

       creates a new namespace containing the variable num and the procedure
       bump.  The commands and variables in this namespace are separate from
       other commands and variables in the same program.  If there is a
       command named bump in the global namespace, for example, it will be
       different from the command bump in the Counter namespace.

       Namespace variables resemble global variables in Tcl.  They exist
       outside of the procedures in a namespace but can be accessed in a
       procedure via the variable command, as shown in the example above.

       Namespaces are dynamic.  You can add and delete commands and variables
       at any time, so you can build up the contents of a namespace over time
       using a series of namespace eval commands.  For example, the following
       series of commands has the same effect as the namespace definition
       shown above:

              namespace eval Counter {
                  variable num 0
                  proc bump {} {
                      variable num
                      return [incr num]
                  }
              }
              namespace eval Counter {
                  proc test {args} {
                      return $args
                  }
              }
              namespace eval Counter {
                   rename test ""
              }

       Note that the test procedure is added to the Counter namespace, and
       later removed via the rename command.

       Namespaces can have other namespaces within them, so they nest
       hierarchically.  A nested namespace is encapsulated inside its parent
       namespace and can not interfere with other namespaces.


QUALIFIED NAMES

       Each namespace has a textual name such as history or ::safe::interp.
       Since namespaces may nest, qualified names are used to refer to
       commands, variables, and child namespaces contained inside namespaces.
       Qualified names are similar to the hierarchical path names for Unix
       files or Tk widgets, except that :: is used as the separator instead of
       / or ..  The topmost or global namespace has the name "" (i.e., an
       empty string), although :: is a synonym.  As an example, the name
       ::safe::interp::create refers to the command create in the namespace
       interp that is a child of namespace ::safe, which in turn is a child of
       the global namespace, ::.

       If you want to access commands and variables from another namespace,
       you must use some extra syntax.  Names must be qualified by the
       namespace that contains them.  From the global namespace, we might
       access the Counter procedures like this:

              Counter::bump 5
              Counter::Reset

       We could access the current count like this:

              puts "count = $Counter::num"

       When one namespace contains another, you may need more than one
       qualifier to reach its elements.  If we had a namespace Foo that
       contained the namespace Counter, you could invoke its bump procedure
       from the global namespace like this:

              Foo::Counter::bump 3

       You can also use qualified names when you create and rename commands.
       For example, you could add a procedure to the Foo namespace like this:

              proc Foo::Test {args} {return $args}

       And you could move the same procedure to another namespace like this:

              rename Foo::Test Bar::Test

       There are a few remaining points about qualified names that we should
       cover.  Namespaces have nonempty names except for the global namespace.
       :: is disallowed in simple command, variable, and namespace names
       except as a namespace separator.  Extra colons in any separator part of
       a qualified name are ignored; i.e. two or more colons are treated as a
       namespace separator.  A trailing :: in a qualified variable or command
       name refers to the variable or command named {}.  However, a trailing
       :: in a qualified namespace name is ignored.


NAME RESOLUTION

       In general, all Tcl commands that take variable and command names
       support qualified names.  This means you can give qualified names to
       such commands as set, proc, rename, and interp alias.  If you provide a
       fully-qualified name that starts with a ::, there is no question about
       what command, variable, or namespace you mean.  However, if the name
       does not start with a :: (i.e., is relative), Tcl follows basic rules
       for looking it up:

       o      Variable names are always resolved by looking first in the
              current namespace, and then in the global namespace.

       o      Command names are always resolved by looking in the current
              namespace first. If not found there, they are searched for in
              every namespace on the current namespace's command path (which
              is empty by default). If not found there, command names are
              looked up in the global namespace (or, failing that, are
              processed by the appropriate namespace unknown handler.)

       o      Namespace names are always resolved by looking in only the
              current namespace.

       In the following example,

              set traceLevel 0
              namespace eval Debug {
                  printTrace $traceLevel
              }

       Tcl looks for traceLevel in the namespace Debug and then in the global
       namespace.  It looks up the command printTrace in the same way.  If a
       variable or command name is not found in either context, the name is
       undefined.  To make this point absolutely clear, consider the following
       example:

              set traceLevel 0
              namespace eval Foo {
                  variable traceLevel 3

                  namespace eval Debug {
                      printTrace $traceLevel
                  }
              }

       Here Tcl looks for traceLevel first in the namespace Foo::Debug.  Since
       it is not found there, Tcl then looks for it in the global namespace.
       The variable Foo::traceLevel is completely ignored during the name
       resolution process.

       You can use the namespace which command to clear up any question about
       name resolution.  For example, the command:

              namespace eval Foo::Debug {namespace which -variable traceLevel}

       returns ::traceLevel.  On the other hand, the command,

              namespace eval Foo {namespace which -variable traceLevel}

       returns ::Foo::traceLevel.

       As mentioned above, namespace names are looked up differently than the
       names of variables and commands.  Namespace names are always resolved
       in the current namespace.  This means, for example, that a namespace
       eval command that creates a new namespace always creates a child of the
       current namespace unless the new namespace name begins with ::.

       Tcl has no access control to limit what variables, commands, or
       namespaces you can reference.  If you provide a qualified name that
       resolves to an element by the name resolution rule above, you can
       access the element.

       You can access a namespace variable from a procedure in the same
       namespace by using the variable command.  Much like the global command,
       this creates a local link to the namespace variable.  If necessary, it
       also creates the variable in the current namespace and initializes it.
       Note that the global command only creates links to variables in the
       global namespace.  It is not necessary to use a variable command if you
       always refer to the namespace variable using an appropriate qualified
       name.


IMPORTING COMMANDS

       Namespaces are often used to represent libraries.  Some library
       commands are used so frequently that it is a nuisance to type their
       qualified names.  For example, suppose that all of the commands in a
       package like BLT are contained in a namespace called Blt.  Then you
       might access these commands like this:

              Blt::graph .g -background red
              Blt::table . .g 0,0

       If you use the graph and table commands frequently, you may want to
       access them without the Blt:: prefix.  You can do this by importing the
       commands into the current namespace, like this:

              namespace import Blt::*

       This adds all exported commands from the Blt namespace into the current
       namespace context, so you can write code like this:

              graph .g -background red
              table . .g 0,0

       The namespace import command only imports commands from a namespace
       that that namespace exported with a namespace export command.

       Importing every command from a namespace is generally a bad idea since
       you do not know what you will get.  It is better to import just the
       specific commands you need.  For example, the command

              namespace import Blt::graph Blt::table

       imports only the graph and table commands into the current context.

       If you try to import a command that already exists, you will get an
       error.  This prevents you from importing the same command from two
       different packages.  But from time to time (perhaps when debugging),
       you may want to get around this restriction.  You may want to reissue
       the namespace import command to pick up new commands that have appeared
       in a namespace.  In that case, you can use the -force option, and
       existing commands will be silently overwritten:

              namespace import -force Blt::graph Blt::table

       If for some reason, you want to stop using the imported commands, you
       can remove them with a namespace forget command, like this:

              namespace forget Blt::*

       This searches the current namespace for any commands imported from Blt.
       If it finds any, it removes them.  Otherwise, it does nothing.  After
       this, the Blt commands must be accessed with the Blt:: prefix.

       When you delete a command from the exporting namespace like this:

              rename Blt::graph ""

       the command is automatically removed from all namespaces that import
       it.


EXPORTING COMMANDS

       You can export commands from a namespace like this:

              namespace eval Counter {
                  namespace export bump reset
                  variable Num 0
                  variable Max 100

                  proc bump {{by 1}} {
                      variable Num
                      incr Num $by
                      Check
                      return $Num
                  }
                  proc reset {} {
                      variable Num
                      set Num 0
                  }
                  proc Check {} {
                      variable Num
                      variable Max
                      if {$Num > $Max} {
                          error "too high!"
                      }
                  }
              }

       The procedures bump and reset are exported, so they are included when
       you import from the Counter namespace, like this:

              namespace import Counter::*

       However, the Check procedure is not exported, so it is ignored by the
       import operation.

       The namespace import command only imports commands that were declared
       as exported by their namespace.  The namespace export command specifies
       what commands may be imported by other namespaces.  If a namespace
       import command specifies a command that is not exported, the command is
       not imported.


SCOPED SCRIPTS

       The namespace code command is the means by which a script may be
       packaged for evaluation in a namespace other than the one in which it
       was created.  It is used most often to create event handlers, Tk
       bindings, and traces for evaluation in the global context.  For
       instance, the following code indicates how to direct a variable trace
       callback into the current namespace:

              namespace eval a {
                  variable b
                  proc theTraceCallback { n1 n2 op } {
                      upvar 1 $n1 var
                      puts "the value of $n1 has changed to $var"
                      return
                  }
                  trace add variable b write [namespace code theTraceCallback]
              }
              set a::b c

       When executed, it prints the message:

              the value of a::b has changed to c


ENSEMBLES

       The namespace ensemble is used to create and manipulate ensemble
       commands, which are commands formed by grouping subcommands together.
       The commands typically come from the current namespace when the
       ensemble was created, though this is configurable.  Note that there may
       be any number of ensembles associated with any namespace (including
       none, which is true of all namespaces by default), though all the
       ensembles associated with a namespace are deleted when that namespace
       is deleted.  The link between an ensemble command and its namespace is
       maintained however the ensemble is renamed.

       Three subcommands of the namespace ensemble command are defined:

       namespace ensemble create ?option value ...?
              Creates a new ensemble command linked to the current namespace,
              returning the fully qualified name of the command created.  The
              arguments to namespace ensemble create allow the configuration
              of the command as if with the namespace ensemble configure
              command.  If not overridden with the -command option, this
              command creates an ensemble with exactly the same name as the
              linked namespace.  See the section ENSEMBLE OPTIONS below for a
              full list of options supported and their effects.

       namespace ensemble configure command ?option? ?value ...?
              Retrieves the value of an option associated with the ensemble
              command named command, or updates some options associated with
              that ensemble command.  See the section ENSEMBLE OPTIONS below
              for a full list of options supported and their effects.

       namespace ensemble exists command
              Returns a boolean value that describes whether the command
              command exists and is an ensemble command.  This command only
              ever returns an error if the number of arguments to the command
              is wrong.

       When called, an ensemble command takes its first argument and looks it
       up (according to the rules described below) to discover a list of words
       to replace the ensemble command and subcommand with.  The resulting
       list of words is then evaluated (with no further substitutions) as if
       that was what was typed originally (i.e. by passing the list of words
       through Tcl_EvalObjv) and returning the result of the command.  Note
       that it is legal to make the target of an ensemble rewrite be another
       (or even the same) ensemble command.  The ensemble command will not be
       visible through the use of the uplevel or info level commands.

   ENSEMBLE OPTIONS
       The following options, supported by the namespace ensemble create and
       namespace ensemble configure commands, control how an ensemble command
       behaves:

       -map   When non-empty, this option supplies a dictionary that provides
              a mapping from subcommand names to a list of prefix words to
              substitute in place of the ensemble command and subcommand words
              (in a manner similar to an alias created with interp alias; the
              words are not reparsed after substitution); if the first word of
              any target is not fully qualified when set, it is assumed to be
              relative to the current namespace and changed to be exactly that
              (that is, it is always fully qualified when read). When this
              option is empty, the mapping will be from the local name of the
              subcommand to its fully-qualified name.  Note that when this
              option is non-empty and the -subcommands option is empty, the
              ensemble subcommand names will be exactly those words that have
              mappings in the dictionary.

       -parameters
              This option gives a list of named arguments (the names being     |
              used during generation of error messages) that are passed by the |
              caller of the ensemble between the name of the ensemble and the  |
              subcommand argument. By default, it is the empty list.

       -prefixes
              This option (which is enabled by default) controls whether the
              ensemble command recognizes unambiguous prefixes of its
              subcommands.  When turned off, the ensemble command requires
              exact matching of subcommand names.

       -subcommands
              When non-empty, this option lists exactly what subcommands are
              in the ensemble.  The mapping for each of those commands will be
              either whatever is defined in the -map option, or to the command
              with the same name in the namespace linked to the ensemble.  If
              this option is empty, the subcommands of the namespace will
              either be the keys of the dictionary listed in the -map option
              or the exported commands of the linked namespace at the time of
              the invocation of the ensemble command.

       -unknown
              When non-empty, this option provides a partial command (to which
              all the words that are arguments to the ensemble command,
              including the fully-qualified name of the ensemble, are
              appended) to handle the case where an ensemble subcommand is not
              recognized and would otherwise generate an error.  When empty
              (the default) an error (in the style of Tcl_GetIndexFromObj) is
              generated whenever the ensemble is unable to determine how to
              implement a particular subcommand.  See UNKNOWN HANDLER
              BEHAVIOUR for more details.

       The following extra option is allowed by namespace ensemble create:

       -command
              This write-only option allows the name of the ensemble created
              by namespace ensemble create to be anything in any existing
              namespace.  The default value for this option is the fully-
              qualified name of the namespace in which the namespace ensemble
              create command is invoked.

       The following extra option is allowed by namespace ensemble configure:

       -namespace
              This read-only option allows the retrieval of the fully-
              qualified name of the namespace which the ensemble was created
              within.

   UNKNOWN HANDLER BEHAVIOUR
       If an unknown handler is specified for an ensemble, that handler is
       called when the ensemble command would otherwise return an error due to
       it being unable to decide which subcommand to invoke. The exact
       conditions under which that occurs are controlled by the -subcommands,
       -map and -prefixes options as described above.

       To execute the unknown handler, the ensemble mechanism takes the
       specified -unknown option and appends each argument of the attempted
       ensemble command invocation (including the ensemble command itself,
       expressed as a fully qualified name). It invokes the resulting command
       in the scope of the attempted call. If the execution of the unknown
       handler terminates normally, the ensemble engine reparses the
       subcommand (as described below) and tries to dispatch it again, which
       is ideal for when the ensemble's configuration has been updated by the
       unknown subcommand handler. Any other kind of termination of the
       unknown handler is treated as an error.

       The result of the unknown handler is expected to be a list (it is an
       error if it is not). If the list is an empty list, the ensemble command
       attempts to look up the original subcommand again and, if it is not
       found this time, an error will be generated just as if the -unknown
       handler was not there (i.e. for any particular invocation of an
       ensemble, its unknown handler will be called at most once.) This makes
       it easy for the unknown handler to update the ensemble or its backing
       namespace so as to provide an implementation of the desired subcommand
       and reparse.

       When the result is a non-empty list, the words of that list are used to
       replace the ensemble command and subcommand, just as if they had been
       looked up in the -map. It is up to the unknown handler to supply all
       namespace qualifiers if the implementing subcommand is not in the
       namespace of the caller of the ensemble command. Also note that when
       ensemble commands are chained (e.g. if you make one of the commands
       that implement an ensemble subcommand into an ensemble, in a manner
       similar to the text widget's tag and mark subcommands) then the rewrite
       happens in the context of the caller of the outermost ensemble. That is
       to say that ensembles do not in themselves place any namespace contexts
       on the Tcl call stack.

       Where an empty -unknown handler is given (the default), the ensemble
       command will generate an error message based on the list of commands
       that the ensemble has defined (formatted similarly to the error message
       from Tcl_GetIndexFromObj). This is the error that will be thrown when
       the subcommand is still not recognized during reparsing. It is also an
       error for an -unknown handler to delete its namespace.


EXAMPLES

       Create a namespace containing a variable and an exported command:

              namespace eval foo {
                  variable bar 0
                  proc grill {} {
                      variable bar
                      puts "called [incr bar] times"
                  }
                  namespace export grill
              }

       Call the command defined in the previous example in various ways.

              # Direct call
              ::foo::grill

              # Use the command resolution path to find the name
              namespace eval boo {
                  namespace path ::foo
                  grill
              }

              # Import into current namespace, then call local alias
              namespace import foo::grill
              grill

              # Create two ensembles, one with the default name and one with a
              # specified name.  Then call through the ensembles.
              namespace eval foo {
                  namespace ensemble create
                  namespace ensemble create -command ::foobar
              }
              foo grill
              foobar grill

       Look up where the command imported in the previous example came from:

              puts "grill came from [namespace origin grill]"

       Remove all imported commands from the current namespace:

              namespace forget {*}[namespace import]

       Create an ensemble for simple working with numbers, using the           |
       -parameters option to allow the operator to be put between the first    |
       and second arguments.                                                   |

              namespace eval do {                                              |
                  namespace export *                                           |
                  namespace ensemble create -parameters x                      |
                  proc plus  {x y} {expr { $x + $y }}                          |
                  proc minus {x y} {expr { $x - $y }}                          |
              }                                                                |

              # In use, the ensemble works like this:                          |
              puts [do 1 plus [do 9 minus 7]]                                  |


SEE ALSO

       interp(n), upvar(n), variable(n)


KEYWORDS

       command, ensemble, exported, internal, variable

Tcl                                   8.5                         namespace(n)

tcl 8.6.14 - Generated Sat Mar 2 15:16:55 CST 2024
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