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diff --git a/doc/namespace.n b/doc/namespace.n new file mode 100644 index 0000000..5bf787d --- /dev/null +++ b/doc/namespace.n @@ -0,0 +1,563 @@ +'\" +'\" Copyright (c) 1993-1997 Bell Labs Innovations for Lucent Technologies +'\" Copyright (c) 1997 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +'\" SCCS: @(#) namespace.n 1.9 97/08/13 17:08:25 +'\" +.so man.macros +.TH namespace n 8.0 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?\fIoption\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 \fIoption\fR's are listed below. +Note that you can abbreviate the \fIoption\fR's. +.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 \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 \fB::\fR is used directly, +otherwise the namespace \fInamespace\fR +(or the fully-qualified name of the current namespace) +is prepended onto the 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 code\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 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 +\fBnamespace 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 VALUES\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 ``'' +(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 doesn't exist, this command returns an error. +If no namespace names are given, this command does nothing. +.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. +.br +.sp +If \fInamespace\fR has leading namespace qualifiers +and any leading namespaces do not exist, +they are automatically created. +.TP +\fBnamespace export \fR?\-\fBclear\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 \-\fBclear\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 \-\fBclear\fR flag isn't 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 qualified name such as +\fBfoo::x\fR or \fBa::b::p*\fR. +Qualified names contain \fB::\fRs and qualify a name +with the name of one or more namespaces. +Each \fIpattern\fR 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. +This command first finds the matching exported commands. +It then checks whether any of those 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. +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. +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 \-\fBforce\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. +.TP +\fBnamespace inscope\fR \fInamespace arg\fR ?\fIarg ...\fR? +Executes a script in the context of a particular namespace. +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 it has \fBlappend\fR semantics +and the namespace must already exist. +It treats the first argument as a list, +and appends any arguments after the first +onto the end as proper list elements. +\fBnamespace inscope ::foo a x y z\fR +is equivalent to +\fBnamespace eval ::foo [concat a [list x y z]]\fR +This \fBlappend\fR semantics is important because many callback scripts +are actually prefixes. +.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 qualifiers\fR \fIstring\fR +Returns any leading namespace qualifiers for \fIstring\fR. +Qualifiers are namespace names separated by \fB::\fRs. +For the \fIstring\fR \fB::foo::bar::x\fR, +this command returns \fB::foo::bar\fR, +and for \fB::\fR it returns \fB``''\fR (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 \fB::\fRs. +For the \fIstring\fR \fB::foo::bar::x\fR, +this command returns \fBx\fR, +and for \fB::\fR it returns \fB``''\fR (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 which\fR ?\-\fBcommand\fR? ?\-\fBvariable\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 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 +won't 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, +.CS +\fBnamespace eval Counter { + namespace export Bump + variable num 0 + + proc Bump {} { + variable num + incr num + } +}\fR +.CE +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: +.CS +\fBnamespace 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 "" +}\fR +.CE +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 ``'' (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 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: +.CS +\fBCounter::Bump 5 +Counter::Reset\fR +.CE +We could access the current count like this: +.CS +\fBputs "count = $Counter::num"\fR +.CE +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: +.CS +\fBFoo::Counter::Bump 3\fR +.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: +.CS +\fBproc Foo::Test {args} {return $args}\fR +.CE +And you could move the same procedure to another namespace like this: +.CS +\fBrename Foo::Test Bar::Test\fR +.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 \fB:\fRs in a qualified name are ignored; +that is, two or more \fB:\fRs 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 a fixed rule for looking it up: +Command and variable names are always resolved +by looking first in the current namespace, +and then in the global namespace. +Namespace names, on the other hand, are always resolved +by looking in only the current namespace. +.PP +In the following example, +.CS +\fBset traceLevel 0 +namespace eval Debug { + printTrace $traceLevel +}\fR +.CE +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: +.CS +\fBset traceLevel 0 +namespace eval Foo { + variable traceLevel 3 + + namespace eval Debug { + printTrace $traceLevel + } +}\fR +.CE +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: +.CS +\fBnamespace eval Foo::Debug {namespace which \-variable traceLevel}\fR +.CE +returns \fB::traceLevel\fR. +On the other hand, the command, +.CS +\fBnamespace eval Foo {namespace which \-variable traceLevel}\fR +.CE +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 a \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: +.CS +\fBBlt::graph .g \-background red +Blt::table . .g 0,0\fR +.CE +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: +.CS +\fBnamespace import Blt::*\fR +.CE +This adds all exported commands from the \fBBlt\fR namespace +into the current namespace context, so you can write code like this: +.CS +\fBgraph .g \-background red +table . .g 0,0\fR +.CE +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 don't know what you will get. +It is better to import just the specific commands you need. +For example, the command +.CS +\fBnamespace import Blt::graph Blt::table\fR +.CE +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: +.CS +\fBnamespace import \-force Blt::graph Blt::table\fR +.CE +If for some reason, you want to stop using the imported commands, +you can remove them with an \fBnamespace forget\fR command, like this: +.CS +\fBnamespace forget Blt::*\fR +.CE +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: +.CS +\fBrename Blt::graph ""\fR +.CE +the command is automatically removed from all namespaces that import it. + +.SH "EXPORTING COMMANDS" +You can export commands from a namespace like this: +.CS +\fBnamespace 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!" + } + } +}\fR +.CE +The procedures \fBBump\fR and \fBReset\fR are exported, +so they are included when you import from the \fBCounter\fR namespace, +like this: +.CS +\fBnamespace import Counter::*\fR +.CE +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 "SEE ALSO" +variable(n) + +.SH KEYWORDS +exported, internal, variable |