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diff --git a/doc/namespace.n b/doc/namespace.n new file mode 100644 index 0000000..b06d27a --- /dev/null +++ b/doc/namespace.n @@ -0,0 +1,969 @@ +'\" +'\" Copyright (c) 1993-1997 Bell Labs Innovations for Lucent Technologies +'\" Copyright (c) 1997 Sun Microsystems, Inc. +'\" Copyright (c) 2000 Scriptics Corporation. +'\" Copyright (c) 2004-2005 Donal K. Fellows. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.so man.macros +.TH namespace n 8.5 Tcl "Tcl Built-In Commands" +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +namespace \- create and manipulate contexts for commands and variables +.SH SYNOPSIS +\fBnamespace \fR?\fIsubcommand\fR? ?\fIarg ...\fR? +.BE +.SH DESCRIPTION +.PP +The \fBnamespace\fR command lets you create, access, and destroy +separate contexts for commands and variables. +See the section \fBWHAT IS A NAMESPACE?\fR below +for a brief overview of namespaces. +The legal values of \fIsubcommand\fR are listed below. +Note that you can abbreviate the \fIsubcommand\fRs. +.TP +\fBnamespace children \fR?\fInamespace\fR? ?\fIpattern\fR? +. +Returns a list of all child namespaces that belong to the +namespace \fInamespace\fR. +If \fInamespace\fR is not specified, +then the children are returned for the current namespace. +This command returns fully-qualified names, +which start with a double colon (\fB::\fR). +If the optional \fIpattern\fR 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 (\fB::\fR) is used directly, +otherwise the namespace \fInamespace\fR +(or the fully-qualified name of the current namespace) +is prepended onto the pattern. +.TP +\fBnamespace code \fIscript\fR +. +Captures the current namespace context for later execution +of the script \fIscript\fR. +It returns a new script in which \fIscript\fR has been wrapped +in a \fBnamespace inscope\fR command. +The new script has two important properties. +First, it can be evaluated in any namespace and will cause +\fIscript\fR to be evaluated in the current namespace +(the one where the \fBnamespace code\fR command was invoked). +Second, additional arguments can be appended to the resulting script +and they will be passed to \fIscript\fR as additional arguments. +For example, suppose the command +\fBset script [namespace code {foo bar}]\fR +is invoked in namespace \fB::a::b\fR. +Then \fBeval $script [list x y]\fR +can be executed in any namespace (assuming the value of +\fBscript\fR has been passed in properly) +and will have the same effect as the command +\fB::namespace eval ::a::b {foo bar x y}\fR. +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 \fBSCOPED SCRIPTS\fR for some examples +of how this is used to create callback scripts. +.TP +\fBnamespace current\fR +. +Returns the fully-qualified name for the current namespace. +The actual name of the global namespace is +.MT +(i.e., an empty string), +but this command returns \fB::\fR for the global namespace +as a convenience to programmers. +.TP +\fBnamespace delete \fR?\fInamespace namespace ...\fR? +. +Each namespace \fInamespace\fR 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. +.TP +\fBnamespace ensemble\fR \fIsubcommand\fR ?\fIarg ...\fR? +. +Creates and manipulates a command that is formed out of an ensemble of +subcommands. See the section \fBENSEMBLES\fR below for further +details. +.TP +\fBnamespace eval\fR \fInamespace arg\fR ?\fIarg ...\fR? +. +Activates a namespace called \fInamespace\fR and evaluates some code +in that context. +If the namespace does not already exist, it is created. +If more than one \fIarg\fR argument is specified, +the arguments are concatenated together with a space between each one +in the same fashion as the \fBeval\fR command, +and the result is evaluated. +.RS +.PP +If \fInamespace\fR has leading namespace qualifiers +and any leading namespaces do not exist, +they are automatically created. +.RE +.TP +\fBnamespace exists\fR \fInamespace\fR +. +Returns \fB1\fR if \fInamespace\fR is a valid namespace in the current +context, returns \fB0\fR otherwise. +.TP +\fBnamespace export \fR?\fB\-clear\fR? ?\fIpattern pattern ...\fR? +. +Specifies which commands are exported from a namespace. +The exported commands are those that can be later imported +into another namespace using a \fBnamespace import\fR 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 \fBnamespace export\fR command is executed. +Each \fIpattern\fR 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 \fIpattern\fR is appended onto the namespace's list of export patterns. +If the \fB\-clear\fR flag is given, +the namespace's export pattern list is reset to empty before any +\fIpattern\fR arguments are appended. +If no \fIpattern\fRs are given and the \fB\-clear\fR flag is not given, +this command returns the namespace's current export list. +.TP +\fBnamespace forget \fR?\fIpattern pattern ...\fR? +. +Removes previously imported commands from a namespace. +Each \fIpattern\fR is a simple or qualified name such as +\fBx\fR, \fBfoo::x\fR or \fBa::b::p*\fR. +Qualified names contain double colons (\fB::\fR) and qualify a name +with the name of one or more namespaces. +Each +.QW "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 +.QW "simple pattern" +this command deletes the matching commands of the +current namespace that were imported from a different namespace. +For +.QW "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 un-does the action of a \fBnamespace import\fR command. +.TP +\fBnamespace import \fR?\fB\-force\fR? ?\fIpattern\fR \fIpattern ...\fR? +. +Imports commands into a namespace, or queries the set of imported +commands in a namespace. When no arguments are present, +\fBnamespace import\fR 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 \fBnamespace forget\fR +(see \fBEXAMPLES\fR below). +.RS +.PP +When \fIpattern\fR arguments are present, +each \fIpattern\fR is a qualified name like +\fBfoo::x\fR or \fBa::p*\fR. +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 \fBNAME RESOLUTION\fR section; it is an error if +no namespace with that name can be found. +.PP +All the commands that match a \fIpattern\fR 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 \fB\-force\fR option is given, +imported commands will silently replace existing commands. +The \fBnamespace import\fR 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 \fBnamespace import\fR command is executed. +If another command is defined and exported in this namespace later on, +it will not be imported. +.RE +.TP +\fBnamespace inscope\fR \fInamespace\fR \fIscript\fR ?\fIarg ...\fR? +. +Executes a script in the context of the specified \fInamespace\fR. +This command is not expected to be used directly by programmers; +calls to it are generated implicitly when applications +use \fBnamespace code\fR commands to create callback scripts +that the applications then register with, e.g., Tk widgets. +The \fBnamespace inscope\fR command is much like the \fBnamespace eval\fR +command except that the \fInamespace\fR must already exist, +and \fBnamespace inscope\fR appends additional \fIarg\fRs +as proper list elements. +.RS +.PP +.CS +\fBnamespace inscope ::foo $script $x $y $z\fR +.CE +.PP +is equivalent to +.PP +.CS +\fBnamespace eval ::foo [concat $script [list $x $y $z]]\fR +.CE +.PP +thus additional arguments will not undergo a second round of substitution, +as is the case with \fBnamespace eval\fR. +.RE +.TP +\fBnamespace origin \fIcommand\fR +. +Returns the fully-qualified name of the original command +to which the imported command \fIcommand\fR 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 +\fIa, b,...,n\fR 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, \fIa\fR. +If \fIcommand\fR does not refer to an imported command, +the command's own fully-qualified name is returned. +.TP +\fBnamespace parent\fR ?\fInamespace\fR? +. +Returns the fully-qualified name of the parent namespace +for namespace \fInamespace\fR. +If \fInamespace\fR is not specified, +the fully-qualified name of the current namespace's parent is returned. +.TP +\fBnamespace path\fR ?\fInamespaceList\fR? +. +Returns the command resolution path of the current namespace. If +\fInamespaceList\fR 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 \fBNAME RESOLUTION\fR below for an +explanation of the rules regarding name resolution. +.TP +\fBnamespace qualifiers\fR \fIstring\fR +. +Returns any leading namespace qualifiers for \fIstring\fR. +Qualifiers are namespace names separated by double colons (\fB::\fR). +For the \fIstring\fR \fB::foo::bar::x\fR, +this command returns \fB::foo::bar\fR, +and for \fB::\fR it returns an empty string. +This command is the complement of the \fBnamespace tail\fR command. +Note that it does not check whether the +namespace names are, in fact, +the names of currently defined namespaces. +.TP +\fBnamespace tail\fR \fIstring\fR +. +Returns the simple name at the end of a qualified string. +Qualifiers are namespace names separated by double colons (\fB::\fR). +For the \fIstring\fR \fB::foo::bar::x\fR, +this command returns \fBx\fR, +and for \fB::\fR it returns an empty string. +This command is the complement of the \fBnamespace qualifiers\fR command. +It does not check whether the namespace names are, in fact, +the names of currently defined namespaces. +.TP +\fBnamespace upvar\fR \fInamespace\fR ?\fIotherVar myVar \fR... +. +This command arranges for zero or more local variables in the current +procedure to refer to variables in \fInamespace\fR. The namespace name is +resolved as described in section \fBNAME RESOLUTION\fR. +The command +\fBnamespace upvar $ns a b\fR has the same behaviour as +\fBupvar 0 ${ns}::a b\fR, with the sole exception of the resolution rules +used for qualified namespace or variable names. +\fBnamespace upvar\fR returns an empty string. +.TP +\fBnamespace unknown\fR ?\fIscript\fR? +. +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 \fIscript\fR 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 \fB::unknown\fR. If no argument +is given, it returns the handler for the current namespace. +.TP +\fBnamespace which\fR ?\fB\-command\fR? ?\fB\-variable\fR? \fIname\fR +. +Looks up \fIname\fR as either a command or variable +and returns its fully-qualified name. +For example, if \fIname\fR 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 \fBvariable\fR command +or through a \fBtrace\fR on the variable, this command will return the +fully-qualified name of the variable. +If no flag is given, \fIname\fR is treated as a command name. +See the section \fBNAME RESOLUTION\fR below for an explanation of +the rules regarding name resolution. +.SH "WHAT IS A NAMESPACE?" +.PP +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 \fIglobal namespace\fR. +The global namespace holds all global variables and commands. +The \fBnamespace eval\fR command lets you create new namespaces. +For example, +.PP +.CS +\fBnamespace eval\fR Counter { + \fBnamespace export\fR bump + variable num 0 + + proc bump {} { + variable num + incr num + } +} +.CE +.PP +creates a new namespace containing the variable \fBnum\fR and +the procedure \fBbump\fR. +The commands and variables in this namespace are separate from +other commands and variables in the same program. +If there is a command named \fBbump\fR in the global namespace, +for example, it will be different from the command \fBbump\fR +in the \fBCounter\fR namespace. +.PP +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 \fBvariable\fR command, +as shown in the example above. +.PP +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 \fBnamespace eval\fR commands. +For example, the following series of commands has the same effect +as the namespace definition shown above: +.PP +.CS +\fBnamespace eval\fR Counter { + variable num 0 + proc bump {} { + variable num + return [incr num] + } +} +\fBnamespace eval\fR Counter { + proc test {args} { + return $args + } +} +\fBnamespace eval\fR Counter { + rename test "" +} +.CE +.PP +Note that the \fBtest\fR procedure is added to the \fBCounter\fR namespace, +and later removed via the \fBrename\fR command. +.PP +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. +.SH "QUALIFIED NAMES" +.PP +Each namespace has a textual name such as +\fBhistory\fR or \fB::safe::interp\fR. +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 \fB::\fR is used as the separator +instead of \fB/\fR or \fB.\fR. +The topmost or global namespace has the name +.MT +(i.e., an empty string), although \fB::\fR is a synonym. +As an example, the name \fB::safe::interp::create\fR +refers to the command \fBcreate\fR in the namespace \fBinterp\fR +that is a child of namespace \fB::safe\fR, +which in turn is a child of the global namespace, \fB::\fR. +.PP +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 \fBCounter\fR procedures like this: +.PP +.CS +Counter::bump 5 +Counter::Reset +.CE +.PP +We could access the current count like this: +.PP +.CS +puts "count = $Counter::num" +.CE +.PP +When one namespace contains another, you may need more than one +qualifier to reach its elements. +If we had a namespace \fBFoo\fR that contained the namespace \fBCounter\fR, +you could invoke its \fBbump\fR procedure +from the global namespace like this: +.PP +.CS +Foo::Counter::bump 3 +.CE +.PP +You can also use qualified names when you create and rename commands. +For example, you could add a procedure to the \fBFoo\fR +namespace like this: +.PP +.CS +proc Foo::Test {args} {return $args} +.CE +.PP +And you could move the same procedure to another namespace like this: +.PP +.CS +rename Foo::Test Bar::Test +.CE +.PP +There are a few remaining points about qualified names +that we should cover. +Namespaces have nonempty names except for the global namespace. +\fB::\fR 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 \fB::\fR in a qualified variable or command name +refers to the variable or command named {}. +However, a trailing \fB::\fR in a qualified namespace name is ignored. +.SH "NAME RESOLUTION" +.PP +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 +\fBset\fR, \fBproc\fR, \fBrename\fR, and \fBinterp alias\fR. +If you provide a fully-qualified name that starts with a \fB::\fR, +there is no question about what command, variable, or namespace +you mean. +However, if the name does not start with a \fB::\fR +(i.e., is \fIrelative\fR), +Tcl follows basic rules for looking it up: +.IP \(bu +\fBVariable names\fR are always resolved by looking first in the current +namespace, and then in the global namespace. +.IP \(bu +\fBCommand names\fR 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 \fBnamespace unknown\fR handler.) +.IP \(bu +\fBNamespace names\fR are always resolved by looking in only the current +namespace. +.PP +In the following example, +.PP +.CS +set traceLevel 0 +\fBnamespace eval\fR Debug { + printTrace $traceLevel +} +.CE +.PP +Tcl looks for \fBtraceLevel\fR in the namespace \fBDebug\fR +and then in the global namespace. +It looks up the command \fBprintTrace\fR 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: +.PP +.CS +set traceLevel 0 +\fBnamespace eval\fR Foo { + variable traceLevel 3 + + \fBnamespace eval\fR Debug { + printTrace $traceLevel + } +} +.CE +.PP +Here Tcl looks for \fBtraceLevel\fR first in the namespace \fBFoo::Debug\fR. +Since it is not found there, Tcl then looks for it +in the global namespace. +The variable \fBFoo::traceLevel\fR is completely ignored +during the name resolution process. +.PP +You can use the \fBnamespace which\fR command to clear up any question +about name resolution. +For example, the command: +.PP +.CS +\fBnamespace eval\fR Foo::Debug {\fBnamespace which\fR \-variable traceLevel} +.CE +.PP +returns \fB::traceLevel\fR. +On the other hand, the command, +.PP +.CS +\fBnamespace eval\fR Foo {\fBnamespace which\fR \-variable traceLevel} +.CE +.PP +returns \fB::Foo::traceLevel\fR. +.PP +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 \fBnamespace eval\fR command that creates a new namespace +always creates a child of the current namespace +unless the new namespace name begins with \fB::\fR. +.PP +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. +.PP +You can access a namespace variable +from a procedure in the same namespace +by using the \fBvariable\fR command. +Much like the \fBglobal\fR 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 \fBglobal\fR command only creates links +to variables in the global namespace. +It is not necessary to use a \fBvariable\fR command +if you always refer to the namespace variable using an +appropriate qualified name. +.SH "IMPORTING COMMANDS" +.PP +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 \fBBlt\fR. +Then you might access these commands like this: +.PP +.CS +Blt::graph .g \-background red +Blt::table . .g 0,0 +.CE +.PP +If you use the \fBgraph\fR and \fBtable\fR commands frequently, +you may want to access them without the \fBBlt::\fR prefix. +You can do this by importing the commands into the current namespace, +like this: +.PP +.CS +\fBnamespace import\fR Blt::* +.CE +.PP +This adds all exported commands from the \fBBlt\fR namespace +into the current namespace context, so you can write code like this: +.PP +.CS +graph .g \-background red +table . .g 0,0 +.CE +.PP +The \fBnamespace import\fR command only imports commands +from a namespace that that namespace exported +with a \fBnamespace export\fR command. +.PP +Importing \fIevery\fR 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 +.PP +.CS +\fBnamespace import\fR Blt::graph Blt::table +.CE +.PP +imports only the \fBgraph\fR and \fBtable\fR commands into the +current context. +.PP +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 \fBnamespace import\fR command to pick up new commands +that have appeared in a namespace. In that case, you can use the +\fB\-force\fR option, and existing commands will be silently overwritten: +.PP +.CS +\fBnamespace import\fR \-force Blt::graph Blt::table +.CE +.PP +If for some reason, you want to stop using the imported commands, +you can remove them with a \fBnamespace forget\fR command, like this: +.PP +.CS +\fBnamespace forget\fR Blt::* +.CE +.PP +This searches the current namespace for any commands imported from \fBBlt\fR. +If it finds any, it removes them. Otherwise, it does nothing. +After this, the \fBBlt\fR commands must be accessed with the \fBBlt::\fR +prefix. +.PP +When you delete a command from the exporting namespace like this: +.PP +.CS +rename Blt::graph "" +.CE +.PP +the command is automatically removed from all namespaces that import it. +.SH "EXPORTING COMMANDS" +You can export commands from a namespace like this: +.PP +.CS +\fBnamespace eval\fR Counter { + \fBnamespace export\fR 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!" + } + } +} +.CE +.PP +The procedures \fBbump\fR and \fBreset\fR are exported, +so they are included when you import from the \fBCounter\fR namespace, +like this: +.PP +.CS +\fBnamespace import\fR Counter::* +.CE +.PP +However, the \fBCheck\fR procedure is not exported, +so it is ignored by the import operation. +.PP +The \fBnamespace import\fR command only imports commands +that were declared as exported by their namespace. +The \fBnamespace export\fR command specifies what commands +may be imported by other namespaces. +If a \fBnamespace import\fR command specifies a command +that is not exported, the command is not imported. +.SH "SCOPED SCRIPTS" +.PP +The \fBnamespace code\fR 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 \fBtrace\fR callback into the current +namespace: +.PP +.CS +\fBnamespace eval\fR 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 [\fBnamespace code\fR theTraceCallback] +} +set a::b c +.CE +.PP +When executed, it prints the message: +.PP +.CS +the value of a::b has changed to c +.CE +.SH ENSEMBLES +.PP +The \fBnamespace ensemble\fR 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. +.PP +Three subcommands of the \fBnamespace ensemble\fR command are defined: +.TP +\fBnamespace ensemble create\fR ?\fIoption value ...\fR? +. +Creates a new ensemble command linked to the current namespace, +returning the fully qualified name of the command created. The +arguments to \fBnamespace ensemble create\fR allow the configuration +of the command as if with the \fBnamespace ensemble configure\fR +command. If not overridden with the \fB\-command\fR option, this +command creates an ensemble with exactly the same name as the linked +namespace. See the section \fBENSEMBLE OPTIONS\fR below for a full +list of options supported and their effects. +.TP +\fBnamespace ensemble configure \fIcommand\fR ?\fIoption\fR? ?\fIvalue ...\fR? +. +Retrieves the value of an option associated with the ensemble command +named \fIcommand\fR, or updates some options associated with that +ensemble command. See the section \fBENSEMBLE OPTIONS\fR below for a +full list of options supported and their effects. +.TP +\fBnamespace ensemble exists\fR \fIcommand\fR +. +Returns a boolean value that describes whether the command +\fIcommand\fR exists and is an ensemble command. This command only +ever returns an error if the number of arguments to the command is +wrong. +.PP +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 \fBTcl_EvalObjv\fR) 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 \fBuplevel\fR or \fBinfo level\fR commands. +.SS "ENSEMBLE OPTIONS" +.PP +The following options, supported by the \fBnamespace ensemble +create\fR and \fBnamespace ensemble configure\fR commands, control how +an ensemble command behaves: +.TP +\fB\-map\fR +. +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 \fBinterp alias\fR; 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 +\fIcurrent\fR 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 +\fB\-subcommands\fR option is empty, the ensemble subcommand names +will be exactly those words that have mappings in the dictionary. +.TP +\fB\-parameters\fR +.VS 8.6 +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. +.VE 8.6 +.TP +\fB\-prefixes\fR +. +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. +.TP +\fB\-subcommands\fR +. +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 \fB\-map\fR 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 \fB\-map\fR option or the exported commands +of the linked namespace at the time of the invocation of the ensemble +command. +.TP +\fB\-unknown\fR +. +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 +\fBTcl_GetIndexFromObj\fR) is generated whenever the ensemble is +unable to determine how to implement a particular subcommand. See +\fBUNKNOWN HANDLER BEHAVIOUR\fR for more details. +.PP +The following extra option is allowed by \fBnamespace ensemble +create\fR: +.TP +\fB\-command\fR +. +This write-only option allows the name of the ensemble created by +\fBnamespace ensemble create\fR to be anything in any existing +namespace. The default value for this option is the fully-qualified +name of the namespace in which the \fBnamespace ensemble create\fR +command is invoked. +.PP +The following extra option is allowed by \fBnamespace ensemble +configure\fR: +.TP +\fB\-namespace\fR +. +This read-only option allows the retrieval of the fully-qualified name +of the namespace which the ensemble was created within. +.SS "UNKNOWN HANDLER BEHAVIOUR" +.PP +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 +\fB\-subcommands\fR, \fB\-map\fR and \fB\-prefixes\fR options as +described above. +.PP +To execute the unknown handler, the ensemble mechanism takes the +specified \fB\-unknown\fR 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. +.PP +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 +\fB\-unknown\fR 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. +.PP +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 \fB\-map\fR. 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 \fBtext\fR 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. +.PP +Where an empty \fB\-unknown\fR 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 \fBTcl_GetIndexFromObj\fR). This is the error that +will be thrown when the subcommand is still not recognized during +reparsing. It is also an error for an \fB\-unknown\fR handler to +delete its namespace. +.SH EXAMPLES +Create a namespace containing a variable and an exported command: +.PP +.CS +\fBnamespace eval\fR foo { + variable bar 0 + proc grill {} { + variable bar + puts "called [incr bar] times" + } + \fBnamespace export\fR grill +} +.CE +.PP +Call the command defined in the previous example in various ways. +.PP +.CS +# Direct call +::foo::grill + +# Use the command resolution path to find the name +\fBnamespace eval\fR boo { + \fBnamespace path\fR ::foo + grill +} + +# Import into current namespace, then call local alias +\fBnamespace import\fR foo::grill +grill + +# Create two ensembles, one with the default name and one with a +# specified name. Then call through the ensembles. +\fBnamespace eval\fR foo { + \fBnamespace ensemble\fR create + \fBnamespace ensemble\fR create -command ::foobar +} +foo grill +foobar grill +.CE +.PP +Look up where the command imported in the previous example came from: +.PP +.CS +puts "grill came from [\fBnamespace origin\fR grill]" +.CE +.PP +Remove all imported commands from the current namespace: +.PP +.CS +namespace forget {*}[namespace import] +.CE +.PP +.VS 8.6 +Create an ensemble for simple working with numbers, using the +\fB\-parameters\fR option to allow the operator to be put between the first +and second arguments. +.PP +.CS +\fBnamespace eval\fR do { + \fBnamespace export\fR * + \fBnamespace ensemble\fR 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]] +.CE +.VE 8.6 +.SH "SEE ALSO" +interp(n), upvar(n), variable(n) +.SH KEYWORDS +command, ensemble, exported, internal, variable +'\" Local Variables: +'\" mode: nroff +'\" End: |