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nx::Object

nx::Object(3) 2.3.0 Object "NX API"

Name

nx::Object - API reference of the base class in the NX object system

Synopsis

Description

nx::Object is the base class of the NX object system. All objects defined in NX are (direct or indirect) instances of this base class. The methods provided by the nx::Object base class are available to all objects and to all classes defined in NX.

 +---------+
 | ::nx::* |
 +---------+--------------------------------------Y
 |                                                |
 |  +---------+     instance of     +----------+  |
 |  |         |<....................|          |  |
 |  |  Class  |                     |  Object  |  |
 |  |         |....................>|          |  |
 |  +----+----+     subclass of     +-----+----+  |
 |       ^                           ^    ^       |
instance.|...........................|....|......./
      of |                           |    |
   +-----+-----+    subclass of      |    | instance
   |           |.....................|    | of
   |   /cls/   |    (by default)          |
   |           |                          |
   +-----------+                          |
         ^                                |
instance |.............(xor)..............|
      of |         +-----------+          |
         |.........|           |..........|
                   |   /obj/   |
                   |           |
                   +-----------+

NX allows for creating and for using objects (e.g. obj) which are instantiated from the base class nx::Object directly. Typical use cases are singletons and anonymous, inline objects. In such use cases, NX does not require creating an intermediate application class (e.g. cls), which specializes the base class nx::Object by default, beforehand.

Objects (e.g. obj) which are creating by instantiating a previously defined application class (e.g. cls) are indirect instances of nx::Object.

Direct instances of nx::Object can be created as follows:

nx::Object create obj ?-object-mixins mixinSpec? ?-class newClassName? ?-object-filters filterSpec? ?initBlock?

To create a direct instance of nx::Object having an explicit name obj, use create on nx::Object. Note that create is defined by nx::Class and is available to nx::Object being an instance of nx::Class. This way, singleton objects can be created, for example.

nx::Object new ?-object-mixins mixinSpec? ?-class newClassName? ?-object-filters filterSpec? ?initBlock?

To create a direct instance of nx::Object having an automatically assigned, implicit object name, use new on nx::Object. Note that new is defined by nx::Class and is available to nx::Object being an instance of nx::Class. Using new allows for creating anonymous, inline objects, for example.

The configuration options for direct and indirect instances of nx::Object, which can be passed when calling create and new, are documented in the subsequent section.

Configuration Options for Instances of nx::Object

Configuration options can be used for configuring objects during their creation by passing the options as non-positional arguments into calls of new and create (see nx::Class). An existing object can be queried for its current configuration using cget and it can be re-configured using configure. Legal configuration options are:

-class ?className?

Retrieves the current class of the object or sets the object's class to className, if provided.

-object-filters ?filterMethods?

Retrieves the list of currently active per-object filter methods or sets a list of per-object filter methods, if filterMethods is provided.

-object-mixins ?mixinSpecs?

If mixinSpecs is not specified, retrieves the list of currently active per-object mixin specifications. If mixinSpecs is specified, sets a list of per-object mixin specifications to become active. mixin classes are returned or set in terms of a list of mixin specifications.

Methods for Instances of nx::Object

alias
obj ?public | private | protected? object alias ?-debug? ?-deprecated? methodName ?-returns valueChecker? ?-frame object | method? cmdName

Define an alias method for the given object. The resulting method registers a pre-existing Tcl command cmdName under the (alias) name methodName with the object. If cmdName refers to another method, the corresponding argument should be a valid method handle. If a Tcl command (e.g., a proc), the argument should be a fully qualified Tcl command name. If aliasing a subcommand (e.g., array exists) of a Tcl namespace ensemble (e.g., array), cmdName must hold the fully qualified subcommand name (and not the ensemble name of the subcommand).

As for a regular object method, -returns allows for setting a value checker on the values returned by the aliased command cmdName.

When creating an alias method for a C-implemented Tcl command (i.e., command defined using the Tcl/NX C-API), -frame sets the scope for variable references used in the aliased command. If the provided value is object, then variable references will be resolved in the context of the called object, i.e., the object upon which the alias method is invoked, as if they were object variables. There is no need for using the colon-prefix notation for identifying object variables. If the value is method, then the aliased command will be executed as a regular method call. The command is aware of its called-object context; i.e., it can resolve ::nx::self. In addition, the alias method has access to the method-call context (e.g., nx::next). If -frame is omitted, and by default, the variable references will resolve in the context of the caller of the alias method.

To express deprecation of the alias method methodName, set the -deprecated flag. Deprecated methods remain usable from client code, but their usage will be signaled to the developer and/or can be tracked using ::nsf::deprecated. To register methodName with the debugger, set the -debug flag. Entering and exiting a method, which was flagged for debugging, is recorded by calling the redefinable callback procs ::nsf::debug::call and ::nsf::debug::exit, respectively. By default, these callbacks forward to ::nsf::log, which can also be customized at the script level.

cget
obj cget configurationOption

The method is used to obtain the current value of configurationOption for obj. The configuration options available for querying through cget are determined by the configurable properties defined by the class hierarchy of obj. The queriable configuration options for obj can be obtained by calling info lookup syntax configure. The configurationOption can be set and modified using configure.

% nx::Object create obj
::obj
% ::obj info lookup syntax configure
?-object-mixins /mixinreg .../? ?-class /class/? ?-object-filters /filterreg .../? ?/__initblock/?
% ::obj cget -class
::nx::Object
configure
obj configure ?configurationOption value ...?

This method sets configuration options on an object. The configuration options available for setting on obj are determined by the configurable properties defined by the class hierarchy of obj. The settable configuration options for obj can be obtained by calling info lookup syntax configure. Furthermore, configure is also called during object construction. Under object construction, it receives the arguments passed into calls of create and new. Options set using configure can be retrieved using cget.

% nx::Class create Foo {:property x}
::Foo
% Foo create f1 -x 101
::f1
% f1 cget -x
101
% f1 configure -x 200
% f1 cget -x
200
contains
obj contains ?-withnew trueFalse? ?-object objectName? ?-class className? cmds

This method acts as a builder for nested object structures. Object and class construction statements passed to this method as its last argument cmds are evaluated in a way so that the receiver object obj becomes the parent of the newly constructed objects and classes. This is realized by setting explicitly the namespace for constructing relatively named objects. Fully qualified object names in cmds evade the nesting.

-withnew requests the automatic rescoping of objects created using new so that they become nested into the receiver object obj, rather than being created in the default namespace for autonamed objects (i.e., ::nsf). If turned off, autonamed objects do not become children of obj.

The parent object objectName to be used instead of obj can be specified using -object. If this explicitly set parent object does not exist prior to calling contains, it will be created on the fly as a direct instance of nx::Object. Alternatively, using -class, a class className other than nx::Object for the on-the-fly creation of objectName can be provided.

% nx::Class create Window {
  :contains {
    #
    # Become children of Window, implicitly
    #
    nx::Class create Header; # Window::Header
    nx::Object create Panel; # Window::Panel
  }
  #
  # Explicitly declared a child of Window using [self]
  #
  nx::Class create [self]::Slider; # Window::Slider
  #
  # Fully-qualified objects do not become nested
  #
  nx::Class create ::Door; # ::Door
}
::Window
% ::Window info children
::Window::Panel ::Window::Header ::Window::Slider
copy
obj copy ?newObjectName?

Creates a full and deep copy of a source object obj. The object's copy features all structural and behavioral properties of the source object, including object variables, per-object methods, nested objects, slot objects, namespaces, filters, mixins, and traces. The copy can be named explicitly, if newObjectName is provided, or it is named automatically (in the spirit of new of nx::Class).

delete
obj delete object feature arg

This method serves as the equivalent to Tcl's rename for removing structural (properties, variables) and behavioral features (methods) of the object:

obj delete object property propertyName
obj delete object variable variableName
obj delete object method methodName

Removes a property propertyName, variable variableName, and method methodName, respectively, previously defined for the scope of the object.

delete object method can be equally used for removing regular methods (see object method), an alias method (see object alias), and a forwarder method (see object forward).

destroy
obj destroy

This method allows for explicitly destructing an object obj, potentially prior to obj being destroyed by the object system (e.g. during the shutdown of the object system upon calling exit):

[nx::Object new] destroy

By providing a custom implementation of destroy, the destruction procedure of obj can be customized. Typically, once the application-specific destruction logic has completed, a custom destroy will trigger the actual, physical object destruction via next.

% [nx::Object create obj {
  :public method destroy {} {
    puts "destroying [self]"
    next; # physical destruction
  }
}] destroy
destroying ::obj

A customized object-destruction scheme can be made shared between the instances of a class, by defining the custom destroy for an application class:

% nx::Class create Foo {
    :method destroy {} {
      puts "destroying [self]"
      next; # physical destruction
    }
}
::Foo
% Foo create f1
::f1
% f1 destroy
destroying ::f1

Physical destruction is performed by clearing the in-memory object storage of obj. This is achieved by passing obj into a call to dealloc provided by nx::Class. A near, scripted equivalent to the C-implemented destroy provided by nx::Object would look as follows:

% Object method destroy {} {
  [:info class] dealloc [self]
}

Note, however, that destroy is protected against application-level redefinition. Trying to evaluate the above script snippet yields:

refuse to overwrite protected method 'destroy'; derive e.g. a subclass!

A custom destroy must be provided as a refinement in a subclass of nx::Object or in a mixin class.

eval
obj eval arg ?arg ...?

Evaluates a special Tcl script for the scope of obj in the style of Tcl's eval. There are, however, notable differences to the standard eval: In this script, the colon-prefix notation is available to dispatch to methods and to access variables of obj. Script-local variables, which are thrown away once the evaluation of the script has completed, can be defined to store intermediate results.

 
  % nx::Object create obj {
    :object property {bar 1}
    :public object method foo {x} { return $x }
  }
  ::obj
  % ::obj eval {
    set y [:foo ${:bar}]
  }
  1
filters
obj object filters submethod ?arg ...?

Accesses and modifies the list of methods which are registered as filters with obj using a specific setter or getter submethod:

obj object filters add spec ?index?

Inserts a single filter into the current list of filters of obj. Using index, a position in the existing list of filters for inserting the new filter can be set. If omitted, index defaults to the list head (0).

obj object filters clear

Removes all filters from obj and returns the list of removed filters. Clearing is equivalent to passing an empty list for filterSpecList to object filter set.

obj object filters delete ?-nocomplain? specPattern

Removes a single filter from the current list of filters of obj whose spec matches specPattern. specPattern can contain special matching chars (see string match). object filters delete will throw an error if there is no matching filter, unless -nocomplain is set.

obj object filters get

Returns the list of current filter specifications registered for obj.

obj object filters guard methodName ?expr?

If expr is specified, registers a guard expression expr with a filter methodName. This requires that the filter methodName has been previously set using object filters set or added using object filters add. expr must be a valid Tcl expression (see expr). An empty string for expr will clear the currently registered guard expression for filter methodName.

If expr is omitted, returns the guard expression set on the filter methodName defined for obj. If none is available, an empty string will be returned.

obj object filters methods ?pattern?

If pattern is omitted, returns all filter names which are defined by obj. By specifying pattern, the returned filters can be limited to those whose names match patterns (see string match).

obj object filters set filterSpecList

filterSpecList takes a list of filter specs, with each spec being itself either a one-element or a two-element list: methodName ?-guard guardExpr?. methodName identifies an existing method of obj which becomes registered as a filter. If having three elements, the third element guardExpr will be stored as a guard expression of the filter. This guard expression must be a valid Tcl expression (see expr). expr is evaluated when obj receives a message to determine whether the filter should intercept the message. Guard expressions allow for realizing context-dependent or conditional filter composition.

Every methodName in a spec must resolve to an existing method in the scope of the object. To access and to manipulate the list of filters of obj, cget|configure -object-filters can also be used.

forward
obj ?public | protected | private? object forward ?-debug? ?-deprecated? methodName ?-prefix prefixName? ?-frame object? ?-returns valueChecker? ?-verbose? ?target? ?arg ...?

Define a forward method for the given object. The definition of a forward method registers a predefined, but changeable list of forwarder arguments under the (forwarder) name methodName. Upon calling the forward method, the forwarder arguments are evaluated as a Tcl command call. That is, if present, target is interpreted as a Tcl command (e.g., a Tcl proc or an object) and the remainder of the forwarder arguments arg as arguments passed into this command. The actual method arguments to the invocation of the forward method itself are appended to the list of forwarder arguments. If target is omitted, the value of methodName is implicitly set and used as target. This way, when providing a fully-qualified Tcl command name as methodName without target, the unqualified methodName (namespace tail) is used as the forwarder name; while the fully-qualified one serves as the target.

As for a regular object method, -returns allows for setting a value checker on the values returned by the resulting Tcl command call. When passing object to -frame, the resulting Tcl command is evaluated in the context of the object receiving the forward method call. This way, variable names used in the resulting execution of a command become resolved as object variables.

To express deprecation of the forward method methodName, set the -deprecated flag. Deprecated methods remain usable from client code, but their usage will be signaled to the developer and/or can be tracked using ::nsf::deprecated. To register methodName with the debugger, set the -debug flag. Entering and exiting a method, which was flagged for debugging, is recorded by calling the redefinable callback procs ::nsf::debug::call and ::nsf::debug::exit, respectively. By default, these callbacks forward to ::nsf::log, which can also be customized at the script level.

The list of forwarder arguments arg can contain as its elements a mix of literal values and placeholders. Placeholders are prefixed with a percent symbol (%) and substituted for concrete values upon calling the forward method. These placeholders allow for constructing and for manipulating the arguments to be passed into the resulting command call on the fly:

  • %method becomes substituted for the name of the forward method, i.e. methodName.

  • %self becomes substituted for the name of the object receiving the call of the forward method.

  • %1 becomes substituted for the first method argument passed to the call of forward method. This requires, in turn, that at least one argument is passed along with the method call.

    Alternatively, %1 accepts an optional argument defaults: {%1 defaults}. defaults must be a valid Tcl list of two elements. For the first element, %1 is substituted when there is no first method argument which can be consumed by %1. The second element is inserted upon availability of a first method argument with the consumed argument being appended right after the second list element. This placeholder is typically used to define a pair of getter/setter methods.

  • {%@index value} becomes substituted for the specified value at position index in the forwarder-arguments list, with index being either a positive integer, a negative integer, or the literal value end (such as in Tcl's lindex). Positive integers specify a list position relative to the list head, negative integers give a position relative to the list tail. Indexes for positioning placeholders in the definition of a forward method are evaluated from left to right and should be used in ascending order.

    Note that value can be a literal or any of the placeholders (e.g., %method, %self). Position prefixes are exempted, they are evaluated as %cmdName-placeholders in this context.

  • {%argclindex list} becomes substituted for the nth element of the provided list , with n corresponding to the number of method arguments passed to the forward method call.

  • %% is substituted for a single, literal percent symbol (%).

  • %cmdName is substituted for the value returned from executing the Tcl command cmdName. To pass arguments to cmdName, the placeholder should be wrapped into a Tcl list: {%cmdName ?arg ...?}.

    Consider using fully-qualified Tcl command names for cmdName to avoid possible name conflicts with the predefined placeholders, e.g., %self vs. %::nx::self.

To disambiguate the names of subcommands or methods, which potentially become called by a forward method, a prefix prefixName can be set using -prefix. This prefix is prepended automatically to the argument following target (i.e., a second argument), if present. If missing, -prefix has no effect on the forward method call.

To inspect and to debug the conversions performed by the above placeholders, setting the switch -verbose will have the command list to be executed (i.e., after substitution) printed using ::nsf::log (debugging level: notice) upon calling the forward method.

info
obj info baseclass

Returns the base class of obj. The base class is the class from which all NX objects are instantiated directly or indirectly (typically nx::Object).

obj info children ?-type className? ?pattern?

Retrieves the list of nested (or aggregated) objects of obj. The resulting list contains the fully qualified names of the nested objects. If -type is set, only nested objects which are direct or indirect instances of class className are returned. Using pattern, only nested objects whose names match pattern are returned. The pattern string can contain special matching characters (see string match). This method allows for introspecting on contains.

obj info class

Returns the fully qualified name of the current nx::Class of obj. In case of re-classification (see configure), the returned class will be different from the nx::Class from which obj was originally instantiated using create or new.

obj info has ?mixin | namespace | type? ?arg ...?
obj info has mixin className

Verifies whether obj has a given nx::Class className registered as a mixin class (returns: true) or not (returns: false).

obj info has namespace

Checks whether the object has a companion Tcl namespace (returns: true) or not (returns: false). The namespace could have been created using, for example, object require namespace.

obj info has type className

Tests whether the nx::Class className is a type of the object (returns: true) or not (returns: false). That is, the method checks whether the object is a direct instance of className or an indirect instance of one of the superclasses of className.

obj info lookup submethod ?arg ...?

A collection of submethods to retrieve structural features (e.g. configuration options, slot objects) and behavioral features (e.g. methods, filters) available for obj from the perspective of a client to obj. Features provided by obj itself and by the classes in its current linearization list are considered.

obj info lookup filter name

Returns the method handle for the filter method name, if currently registered. If there is no filter name registered, an empty string is returned.

obj info lookup filters ?-guards? ?namePattern?

Returns the method handles of all filters which are active on obj. By turning on the switch -guards, the corresponding guard expressions, if any, are also reported for each filter as a three-element list: methodHandle -guard guardExpr. The returned filters can be limited to those whose names match namePattern (see string match).

obj info lookup method name

Returns the method handle for a method name if a so-named method can be invoked on obj. If there is no method name, an empty string is returned.

obj info lookup methods ?namePattern?

Returns the names of all methods (including aliases and forwarders) which can be invoked on obj. The returned methods can be limited to those whose names match namePattern (see string match).

obj info lookup mixins ?-guards? ?namePattern?

Returns the object names of all mixin classes which are currently active on obj. By turning on the switch -guards, the corresponding guard expressions, if any, are also reported as a three-element list for each mixin class: className -guard guardExpr. The returned mixin classes can be limited to those whose names match namePattern (see string match).

obj info lookup parameters methodName ?namePattern?

Returns the parameter specification of the method methodName callable on obj as a list of parameter names and type specifications. The resulting parameter specification can be limited to those parameters whose names match namePattern (see string match).

obj info lookup slots ?-type className? ?-source all | application | system? ?namePattern?

Returns the command names of all slot objects responsible for managing properties, variables, and relations of obj. The returned slot objects can be limited according to any or a combination of the following criteria: First, slot objects can be filtered based on their command names matching namePattern (see string match). Second, -type allows one to select slot objects which are instantiated from a subclass className of nx::Slot (default: nx::Slot) . Third, -source restricts slot objects returned according to their provenance in either the NX system classes or the application classes present in the linearization list of obj (default: all).

To extract details of each slot object, use the info submethods available for each slot object.

obj info lookup syntax methodName ?namePattern?

Returns the method parameters of the method methodName callable on obj as a concrete-syntax description to be used in human-understandable messages (e.g., errors or warnings, documentation strings). The result can be limited to those parameters matching the namePattern (see string match).

obj info lookup variables

Returns the command names of all slot objects responsible for managing properties and variables of obj, if provided by obj or the classes in the linearization list of obj.

This is equivalent to calling: obj info lookup slots -type ::nx::VariableSlot -source all ?namePattern?.

To extract details of each slot object, use the info submethods available for each slot object.

obj info name

Returns the unqualified name of an object, i.e., the object name without any namespace qualifiers.

obj info info ?-asList?

Returns the available submethods of the info method ensemble for obj, either as a pretty-printed string or as a Tcl list (if the switch -asList is set) for further processing.

obj info object filters ?-guards? ?pattern?

If pattern is omitted, returns all filter names which are defined by obj. By turning on the switch -guards, the corresponding guard expressions, if any, are also reported along with each filter as a three-element list: filterName -guard guardExpr. By specifying pattern, the returned filters can be limited to those whose names match patterns (see string match).

obj info object method option methodName

This introspection submethod provides access to the details of methodName provided by obj. If methodName is not the name of an existing method, an empty string is returned. To disambiguate between a non-existing method and an empty string as valid return value (e.g., for info object method args|parameters|args|...), use info object method exists.

Permitted values for option are:

  • args returns a list containing the parameter names of methodName, in order of the method-parameter specification.

  • body returns the body script of methodName.

  • callprotection returns the call-protection level set for methodName; possible values: public, protected, private.

  • debug returns 1 if methodName is in debug mode, 0 otherwise.

  • definition returns a canonical command list which allows for (re-)define methodName.

  • definitionhandle returns the method handle for a submethod in a method ensemble from the perspective of obj as method provider. methodName must contain a complete method path.

  • deprecated returns 1 if methodName is deprecated, 0 otherwise.

  • exists returns 1 if there is a methodName provided by obj, returns 0 otherwise.

  • handle returns the method handle for methodName.

  • origin returns the aliased command if methodName is an alias method, or an empty string otherwise.

  • parameters returns the parameter specification of methodName as a list of parameter names and type specifications.

  • registrationhandle returns the method handle for a submethod in a method ensemble from the perspective of the method caller. methodName must contain a complete method path.

  • returns gives the type specification defined for the return value of methodName.

  • submethods returns the names of all submethods of methodName, if methodName is a method ensemble. Otherwise, an empty string is returned.

  • syntax returns the method parameters of methodName as a concrete-syntax description to be used in human-understandable messages (e.g., errors or warnings, documentation strings).

  • type returns whether methodName is a scripted method, an alias method, a forwarder method, or a setter method.

obj info object methods ?-callprotection level? ?-type methodType? ?-path? ?namePattern?

Returns the names of all methods defined by obj. Methods covered include those defined using object alias and object forward. The returned methods can be limited to those whose names match namePattern (see string match).

By setting -callprotection, only methods of a certain call protection level (public, protected, or private) will be returned. Methods of a specific type can be requested using -type. The recognized values for methodType are:

  • scripted denotes methods defined using object method;

  • alias denotes alias methods defined using object alias;

  • forwarder denotes forwarder methods defined using object forward;

  • setter denotes methods defined using ::nsf::setter;

  • all returns methods of any type, without restrictions (also the default value);

obj info object mixins ?-guards? ?pattern?

If pattern is omitted, returns the object names of the mixin classes which extend obj directly. By turning on the switch -guards, the corresponding guard expressions, if any, are also reported along with each mixin as a three-element list: className -guard guardExpr. The returned mixin classes can be limited to those whose names match patterns (see string match).

obj info object slots ?-type className? ?pattern?

If pattern is not specified, returns the object names of all slot objects defined by obj. The returned slot objects can be limited according to any or a combination of the following criteria: First, slot objects can be filtered based on their command names matching pattern (see string match). Second, -type allows one to select slot objects which are instantiated from a subclass className of nx::Slot (default: nx::Slot).

obj info object variables ?pattern?

If pattern is omitted, returns the object names of all slot objects provided by obj which are responsible for managing properties and variables of obj. Otherwise, only slot objects whose names match pattern are returned.

This is equivalent to calling: obj info object slots -type ::nx::VariableSlot pattern.

To extract details of each slot object, use the info submethods available for each slot object.

obj info parent

Returns the fully qualified name of the parent object of obj, if any. If there is no parent object, the name of the Tcl namespace containing obj (e.g. "::") will be reported.

obj info precedence ?-intrinsic? ?pattern?

Lists the classes from which obj inherits structural (e.g. properties) and behavioral features (e.g. methods) and methods, in order of the linearization scheme in NX. By setting the switch -intrinsic, only classes which participate in superclass/subclass relationships (i.e., intrinsic classes) are returned. If a pattern is provided only classes whose names match pattern are returned. The pattern string can contain special matching characters (see string match).

obj info variable option handle

Retrieves selected details about a variable represented by the given handle. A handle can be obtained by querying obj using info object variables and info lookup variables. Valid values for option are:

  • name returns the variable name.

  • parameter returns a canonical parameter specification eligible to (re-)define the given variable (e.g. using object variable) in a new context.

  • definition returns a canonical representation of the definition command used to create the variable in its current configuration.

obj info vars ?pattern?

Yields a list of Tcl variable names created and defined for the scope of obj, i.e., object variables. The list can be limited to object variables whose names match pattern. The pattern string can contain special matching characters (see string match).

method
obj ?public | protected | private? object method ?-debug? ?-deprecated? name parameters ?-checkalways? ?-returns valueChecker? body

Defines a scripted method methodName for the scope of the object. The method becomes part of the object's signature interface. Besides a methodName, the method definition specifies the method parameters and a method body.

parameters accepts a Tcl list containing an arbitrary number of non-positional and positional parameter definitions. Each parameter definition comprises a parameter name, a parameter-specific value checker, and parameter options.

The body contains the method implementation as a script block. In this body script, the colon-prefix notation is available to denote an object variable and a self call. In addition, the context of the object receiving the method call (i.e., the message) can be accessed (e.g., using nx::self) and the call stack can be introspected (e.g., using nx::current).

Optionally, -returns allows for setting a value checker on values returned by the method implementation. By setting the switch -checkalways, value checking on arguments and return value is guaranteed to be performed, even if value checking is temporarily disabled; see nx::configure).

To express deprecation of the method name, set the -deprecated flag. Deprecated methods remain usable from client code, but their usage will be signaled to the developer and/or can be tracked using ::nsf::deprecated. To register name with the debugger, set the -debug flag. Entering and exiting a method, which was flagged for debugging, is recorded by calling the redefinable callback procs ::nsf::debug::call and ::nsf::debug::exit, respectively. By default, these callbacks forward to ::nsf::log, which can also be customized at the script level.

A method closely resembles a Tcl proc, but it differs in some important aspects: First, a method can define non-positional parameters and value checkers on arguments. Second, the script implementing the method body can contain object-specific notation and commands (see above). Third, method calls cannot be intercepted using Tcl trace. Note that an existing Tcl proc can be registered as an alias method with the object (see object alias).

move
obj move newObjectName

Effectively renames an object. First, the source object obj is cloned into a target object newObjectName using copy. Second, the source object obj is destroyed by invoking destroy. move is also called internally when rename is performed for a Tcl command representing an object.

mixins
obj object mixins submethod ?arg ...?

Accesses and modifies the list of mixin classes of obj using a specific setter or getter submethod:

obj object mixins add spec ?index?

Inserts a single mixin class into the current list of mixin classes of obj. Using index, a position in the existing list of mixin classes for inserting the new mixin class can be set. If omitted, index defaults to the list head (0).

obj object mixins classes ?pattern?

If pattern is omitted, returns the object names of the mixin classes which extend obj directly. By specifying pattern, the returned mixin classes can be limited to those whose names match pattern (see string match).

obj object mixins clear

Removes all mixin classes from obj and returns the list of removed mixin classes. Clearing is equivalent to passing an empty list for mixinSpecList to object mixins set.

obj object mixins delete ?-nocomplain? specPattern

Removes a mixin class from a current list of mixin classes of obj whose spec matches specPattern. specPattern can contain special matching chars (see string match). object mixins delete will throw an error if there is no matching mixin class, unless -nocomplain is set.

obj object mixins get

Returns the list of current mixin specifications.

obj object mixins guard className ?expr?

If expr is specified, a guard expression expr is registered with the mixin class className. This requires that the corresponding mixin class className has been previously set using object mixins set or added using object mixins add. expr must be a valid Tcl expression (see expr). An empty string for expr will clear the currently registered guard expression for the mixin class className.

If expr is not specified, returns the active guard expression. If none is available, an empty string will be returned.

obj object mixins set mixinSpecList

mixinSpecList represents a list of mixin class specs, with each spec being itself either a one-element or a three-element list: className ?-guard guardExpr?. If having one element, the element will be considered the className of the mixin class. If having three elements, the third element guardExpr will be stored as a guard expression of the mixin class. This guard expression will be evaluated using expr when obj receives a message to determine if the mixin is to be considered during method dispatch or not. Guard expressions allow for realizing context-dependent or conditional mixin composition.

At the time of setting the mixin relation, that is, calling object mixins, every className as part of a spec must be an existing instance of nx::Class. To access and to manipulate the list of mixin classes of obj, cget|configure -object-mixins can also be used.

__object_configureparameter
obj __object_configureparameter

Computes and returns the configuration options available for obj, to be consumed as method-parameter specification by configure.

property
obj object property ?-accessor public | protected | private? ?-class className? ?-configurable trueFalse? ?-incremental? ?-nocomplain? ?-trace set | get | default? spec ?initBlock?

Defines a property for the scope of the object. The spec provides the property specification as a list holding at least one element or, maximum, two elements: propertyName?:typeSpec? ?defaultValue?. The propertyName is also used as to form the names of the getter/setter methods, if requested (see -accessor). It is, optionally, equipped with a typeSpec following a colon delimiter which specifies a value checker for the values which become assigned to the property. The second, optional element sets a defaultValue for this property.

If -accessor is set, a property will provide for different getter and setter methods:

obj propertyName exists

Returns 1 if the value store of propertyName (e.g., an object variable) exists and has been given a value, returns 0 otherwise.

obj propertyName set value

Sets the property propertyName to value.

obj propertyName get

Returns the current value of property propertyName.

obj propertyName unset

Removes the value store of propertyName (e.g., an object variable), if existing.

The option value passed along -accessor sets the level of call protection for the generated getter and setter methods: public, protected, or private. By default, no getter and setter methods are created.

Turning on the switch -incremental provides a refined setter interface to the value managed by the property. First, setting -incremental implies requesting -accessor (set to public by default, if not specified explicitly). Second, the managed value will be considered a valid Tcl list. A multiplicity of 1..* is set by default, if not specified explicitly as part of spec. Third, to manage this list value element-wise (incrementally), two additional setter methods become available:

obj propertyName add element ?index?

Adding element to the managed list value, at the list position given by index (by default: 0).

obj propertyName delete ?-nocomplain? elementPattern

Removing the first occurrence of an element from the managed list value which matches elementPattern. elementPattern can contain matching characters (see string match). An error will be thrown if there is no match, unless -nocomplain is set.

By setting -configurable to true (the default), the property can be accessed and modified through cget and configure, respectively. If false, no configuration option will become available via cget and configure.

If neither -accessor nor -configurable are requested, the value managed by the property will have to be accessed and modified directly. If the property manages an object variable, its value will be readable and writable using set and eval.

The -trace option causes certain slot methods to be executed whenever get, set, or default operations are invoked on the property:

  • set: slot value=set obj propertyName value

  • get: slot value=get obj propertyName

  • default: slot value=default obj propertyName

A property becomes implemented by a slot object under any of the following conditions:

  • -configurable equals true (by default).

  • -accessor is one of public, protected, or private.

  • -incremental is turned on.

  • initBlock is a non-empty string.

Assuming default settings, every property is realized by a slot object.

Provided a slot object managing the property is to be created, a custom class className from which this slot object is to be instantiated can be set using -class. The default value is ::nx::VariableSlot.

The last argument initBlock accepts an optional Tcl script which is passed into the initialization procedure (see configure) of the property's slot object. See also initBlock for create and new .

By default, the property will ascertain that no (potentially) pre-existing and equally named object variable will be overwritten when defining the property. In case of a conflict, an error exception is thrown:

% Object create obj { set :x 1 }
::obj
% ::obj object property {x 2}
object ::obj has already an instance variable named 'x'

If the switch -nocomplain is on, this check is omitted (continuing the above example):

% ::obj object property -nocomplain {x 2}
% ::obj eval {set :x}
2
require
obj require namespace

Create a Tcl namespace named after the object obj. All object variables become available as namespace variables.

obj require ?public | protected | private? object method methodName

Attempts to register a method definition made available using ::nsf::method::provide under the name methodName with obj . The registered method is subjected to default call protection (protected), if not set explicitly.

unknown
obj unknown unknownMethodName ?arg ...?

This method is called implicitly whenever an unknown method is invoked. unknownMethodName indicates the unresolvable method name, followed by the remainder of the original argument vector as a number of arg of the calling method invocation.

uplevel
obj uplevel ?level? arg1 ?arg2 ...?

Evaluate a script or a command at a different stack-frame level. The command behaves in essence like Tcl's uplevel, but can be used to achieve identical results when filters or mixins are registered.

  • If the level specifier is omitted, uplevel will skip any auxiliary frames added to the stack by active filters and mixins. The resulting stack-frame level corresponds to the callinglevel as indicated by nx::current. In this case method uplevel can be used to evaluate the command in the next enclosing procedure call, i.e., a frame corresponding to a proc, method, or apply call, while skipping frames of filters and mixins.

  • If the level specifier is provided (relative, or absolute), uplevel will execute the command in the stack-frame level. In such cases, method uplevel behaves like Tcl's uplevel command.

 
  % nx::Object create ::obj
  ::obj  
  % ::obj public object method foo {varName} {
      :uplevel set $varName 1; return
  }
  ::obj::foo
  % namespace eval ::ns1 {
       ::obj foo BAR
  }
  % namespace eval ::ns1 {
      info exists BAR
  }
  1

Note, in the example above, uplevel is guaranteed to resolve to the calling context of foo (ns1) despite mixins and filters being (potentially) registered on obj.

upvar
obj upvar ?level? otherVar1 localVar1 ?otherVar2 localVar2 ...?

Links one or more local variables to variables defined in other scopes (namespaces, objects, call frames). The command behaves in essence like Tcl's upvar, but can be used to achieve identical results when filters or mixins are registered.

  • If the level specifier is omitted, upvar will skip any auxiliary frames added to the stack by active filters and mixins. The resulting stack-frame level corresponds to the callinglevel as indicated by nx::current. Therefore, method upvar gives access to the next enclosing procedure call, i.e., a frame corresponding to a proc, method, or apply call, while skipping frames of filters and mixins.

  • If the level specifier is provided (relative, or absolute), upvar will link into the requested stack-frame level. In these cases, method upvar behaves like Tcl's upvar command.

 
  % nx::Object create ::obj
  ::obj  
  % ::obj public object method foo {varName} {
      :upvar $varName x; set x 1; return
  }
  ::obj::foo
  % namespace eval ::ns1 {
       ::obj foo BAR
  }
  % namespace eval ::ns1 {
      info exists BAR
  }
  1

Note, in the example above, upvar is guaranteed to resolve to the calling context of foo (ns1) despite mixins and filters being (potentially) registered on obj.

variable
obj object variable ?-accessor public | protected | private? ?-incremental? ?-class className? ?-configurable trueFalse? ?-initblock script? ?-trace set | get | default? ?-nocomplain? spec ?defaultValue?

Defines a variable for the scope of the object. The spec provides the variable specification: variableName?:typeSpec?. The variableName will be used to name the underlying Tcl variable and the getter/setter methods, if requested (see -accessor). spec is optionally equipped with a typeSpec following a colon delimiter which specifies a value checker for the values managed by the variable. Optionally, a defaultValue can be defined.

If -accessor is set explicitly, a variable will provide for getter and setter methods:

obj variableName exists

Returns 1 if the value store of variableName (e.g., an object variable) exists and has been given a value, returns 0 otherwise.

obj variableName set varValue

Sets variableName to varValue.

obj variableName get

Returns the current value of variableName.

obj variableName unset

Removes variableName, if existing, underlying the property.

The option value passed along -accessor sets the level of call protection for the getter and setter methods: public, protected, or private. By default, no getter and setter methods are created.

Turning on the switch -incremental provides a refined setter interface to the value managed by the variable. First, setting -incremental implies requesting -accessor (public by default, if not specified explicitly). Second, the managed value will be considered a valid Tcl list. A multiplicity of 1..* is set by default, if not specified explicitly as part of spec (see above). Third, to manage this list value element-wise (incrementally), two additional setter operations become available:

obj variableName add element ?index?

Adding element to the managed list value, at the list position given by index (by default: 0).

obj variableName delete ?-nocomplain? elementPattern

Removing the first occurrence of an element from the managed list value which matches elementPattern. elementPattern can contain matching characters (see string match). An error will be thrown if there is no match, unless -nocomplain is set.

By setting -configurable to true, the variable can be accessed and modified via cget and configure, respectively. If false (the default), the interface based on cget and configure will not become available. In this case, and provided that -accessor is set, the variable can be accessed and modified via the getter/setter methods. Alternatively, the underlying Tcl variable, which is represented by the variable, can always be accessed and modified directly, e.g., using eval. By default, -configurable is false.

The -trace option causes certain slot methods to be executed whenever get, set, or default operations are invoked on the variable:

  • set: slot value=set obj variableName value

  • get: slot value=get obj variableName

  • default: slot value=default obj variableName

A variable becomes implemented by a slot object under any of the following conditions:

  • -configurable equals true.

  • -accessor is one of public, protected, or private.

  • -incremental is turned on.

  • -initblock is a non-empty string.

Provided a slot object managing the variable is to be created, a custom class className from which this slot object is to be instantiated can be set using -class. The default value is ::nx::VariableSlot.

Using -initblock, an optional Tcl script can be defined which becomes passed into the initialization procedure (see configure) of the variable's slot object. See also initBlock for create and new .

By default, the variable will ascertain that a pre-existing and equally named object variable will not be overwritten when defining the variable. In case of a conflict, an error exception is thrown:

% Object create obj { set :x 1 }
::obj
% ::obj object variable x 2
object ::obj has already an instance variable named 'x'

If the switch -nocomplain is on, this check is omitted (continuing the above example):

% ::obj object variable -nocomplain x 2
% ::obj eval {set :x}
2

Object Self-Reference

Objects are naturally recursive, with methods of an object ::obj frequently invoking other methods in the same object ::obj and accessing ::obj's object variables. To represent these self-references effectively in method bodies, and depending on the usage scenario, NX offers two alternative notations for self-references: one based on a special-purpose syntax token ("colon prefix"), the other based on the command nx::current.

Both, the colon-prefix notation and nx::current, may be used only in method bodies and scripts passed to eval. If they appear anywhere else, an error will be reported. There are three main use cases for self-references:

  1. As a placeholder for the currently active object, nx::current can be used to retrieve the object name.

  2. Reading and writing object variables directly (i.e. without getter/setter methods in place) require the use of variable names carrying the prefix : ("colon-prefix notation"). Internally, colon-prefixed variable names are processed using Tcl's variable resolvers. Alternatively, one can provide for getter/setter methods for object variables (see property and variable).

  3. Self-referential method calls can be defined via prefixing (:) the method names or, alternatively, via nx::current. Internally, colon-prefixed method names are processed using Tcl's command resolvers. The colon-prefix notation is recommended, also because it has a (slight) performance advantage over nx::current which requires two rather than one command evaluation per method call.

See the following listing for some examples corresponding to use cases 1--3:

  Object create ::obj {
    # 1) print name of currently active object ('::obj')
    puts [current];
    # 2) object variables
    set :x 1; :object variable y 2;	
    :public object method print {} {
      # 2.a) method-local variable
      set z 3;
      # 2.b) variable substitution using '$' and ':'
      puts ${:x}-${:y}-$z;
      # 2.c) reading variables using 'set'
      puts [set :x]-[set :y]-[set z];
      # 2.d) writing variables using 'set', 'incr', ...
      set :x 1; incr :y; 			
    }
    :public object method show {} {
      # 3.a) self-referential method call using ':'	
      :print;
      # 3.b) self-referential method call using 'nx::current'
      [current] print;
      # 3.c) self-referential method call using 'nx::current object'
      [current object] print;              
    }
    :show
  }
 
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