Overview
| Artifact ID: | 2ce3838a45b96217f72f09ad9d209ca5d7430b4fbf0abdbaa3e3a19c215a1402 |
|---|---|
| Ticket: | 050ac21f736d16ba51c1eb4de5ab3f3ce0982c84 |
| Date: | 2019-10-10 16:14:31 |
| User: | schmitzu |
| Artifact Attached: | 365162676e195950a316d47d0454e65026ca8e0945a475449c6608a68505e07d |
| Filename: | class.n |
| Description: | Documentation of "info -scope" added. |
Content:
'\" '\" Copyright (c) 1993-1998 Lucent Technologies, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" .TH class n "" itcl "[incr\ Tcl]" .so man.macros .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME itcl::class \- create a class of objects .SH SYNOPSIS .nf \fBitcl::class \fIclassName \fB{\fR \fBinherit \fIbaseClass\fR ?\fIbaseClass\fR...? \fBconstructor \fIargs\fR ?\fIinit\fR? \fIbody\fR \fBdestructor \fIbody\fR \fBmethod \fIname\fR ?\fIargs\fR? ?\fIbody\fR? \fBproc \fIname\fR ?\fIargs\fR? ?\fIbody\fR? \fBvariable \fIvarName\fR ?\fIinit\fR? ?\fIconfig\fR? \fBcommon \fIvarName\fR ?\fIinit\fR? \fBpublic \fIcommand\fR ?\fIarg arg ...\fR? \fBprotected \fIcommand\fR ?\fIarg arg ...\fR? \fBprivate \fIcommand\fR ?\fIarg arg ...\fR? \fBset \fIvarName\fR ?\fIvalue\fR? \fBarray \fIoption\fR ?\fIarg arg ...\fR? \fB}\fR \fIclassName objName\fR ?\fIarg arg ...\fR? \fIobjName method\fR ?\fIarg arg ...\fR? \fIclassName::proc\fR ?\fIarg arg ...\fR? .fi .BE .SH DESCRIPTION .PP The fundamental construct in \fB[incr\ Tcl]\fR is the class definition. Each class acts as a template for actual objects that can be created. The class itself is a namespace which contains things common to all objects. Each object has its own unique bundle of data which contains instances of the "variables" defined in the class definition. Each object also has a built-in variable named "this", which contains the name of the object. Classes can also have "common" data members that are shared by all objects in a class. .PP Two types of functions can be included in the class definition. "Methods" are functions which operate on a specific object, and therefore have access to both "variables" and "common" data members. "Procs" are ordinary procedures in the class namespace, and only have access to "common" data members. .PP If the body of any method or proc starts with "\fB@\fR", it is treated as the symbolic name for a C procedure. Otherwise, it is treated as a Tcl code script. See below for details on registering and using C procedures. .PP A class can only be defined once, although the bodies of class methods and procs can be defined again and again for interactive debugging. See the \fBbody\fR and \fBconfigbody\fR commands for details. .PP Each namespace can have its own collection of objects and classes. The list of classes available in the current context can be queried using the "\fBitcl::find classes\fR" command, and the list of objects, with the "\fBitcl::find objects\fR" command. .PP A class can be deleted using the "\fBdelete class\fR" command. Individual objects can be deleted using the "\fBdelete object\fR" command. .SH "CLASS DEFINITIONS" .TP \fBclass \fIclassName definition\fR . Provides the definition for a class named \fIclassName\fR. If the class \fIclassName\fR already exists, or if a command called \fIclassName\fR exists in the current namespace context, this command returns an error. If the class definition is successfully parsed, \fIclassName\fR becomes a command in the current context, handling the creation of objects for this class. .PP The class \fIdefinition\fR is evaluated as a series of Tcl statements that define elements within the class. The following class definition commands are recognized: .RS .TP \fBinherit \fIbaseClass\fR ?\fIbaseClass\fR...? . Causes the current class to inherit characteristics from one or more base classes. Classes must have been defined by a previous \fBclass\fR command, or must be available to the auto-loading facility (see "AUTO-LOADING" below). A single class definition can contain no more than one \fBinherit\fR command. .RS .PP The order of \fIbaseClass\fR names in the \fBinherit\fR list affects the name resolution for class members. When the same member name appears in two or more base classes, the base class that appears first in the \fBinherit\fR list takes precedence. For example, if classes "Foo" and "Bar" both contain the member "x", and if another class has the "\fBinherit\fR" statement: .PP .CS inherit Foo Bar .CE .PP then the name "x" means "Foo::x". Other inherited members named "x" must be referenced with their explicit name, like "Bar::x". .RE .TP \fBconstructor \fIargs\fR ?\fIinit\fR? \fIbody\fR . Declares the \fIargs\fR argument list and \fIbody\fR used for the constructor, which is automatically invoked whenever an object is created. .RS .PP Before the \fIbody\fR is executed, the optional \fIinit\fR statement is used to invoke any base class constructors that require arguments. Variables in the \fIargs\fR specification can be accessed in the \fIinit\fR code fragment, and passed to base class constructors. After evaluating the \fIinit\fR statement, any base class constructors that have not been executed are invoked automatically without arguments. This ensures that all base classes are fully constructed before the constructor \fIbody\fR is executed. By default, this scheme causes constructors to be invoked in order from least- to most-specific. This is exactly the opposite of the order that classes are reported by the \fBinfo heritage\fR command. .PP If construction is successful, the constructor always returns the object name\-regardless of how the \fIbody\fR is defined\-and the object name becomes a command in the current namespace context. If construction fails, an error message is returned. .RE .TP \fBdestructor \fIbody\fR . Declares the \fIbody\fR used for the destructor, which is automatically invoked when an object is deleted. If the destructor is successful, the object data is destroyed and the object name is removed as a command from the interpreter. If destruction fails, an error message is returned and the object remains. .RS .PP When an object is destroyed, all destructors in its class hierarchy are invoked in order from most- to least-specific. This is the order that the classes are reported by the "\fBinfo heritage\fR" command, and it is exactly the opposite of the default constructor order. .RE .TP \fBmethod \fIname\fR ?\fIargs\fR? ?\fIbody\fR? . Declares a method called \fIname\fR. When the method \fIbody\fR is executed, it will have automatic access to object-specific variables and common data members. .RS .PP If the \fIargs\fR list is specified, it establishes the usage information for this method. The \fBbody\fR command can be used to redefine the method body, but the \fIargs\fR list must match this specification. .PP Within the body of another class method, a method can be invoked like any other command\-simply by using its name. Outside of the class context, the method name must be prefaced an object name, which provides the context for the data that it manipulates. Methods in a base class that are redefined in the current class, or hidden by another base class, can be qualified using the "\fIclassName\fR::\fImethod\fR" syntax. .RE .TP \fBproc \fIname\fR ?\fIargs\fR? ?\fIbody\fR? . Declares a proc called \fIname\fR. A proc is an ordinary procedure within the class namespace. Unlike a method, a proc is invoked without referring to a specific object. When the proc \fIbody\fR is executed, it will have automatic access only to common data members. .RS .PP If the \fIargs\fR list is specified, it establishes the usage information for this proc. The \fBbody\fR command can be used to redefine the proc body, but the \fIargs\fR list must match this specification. .PP Within the body of another class method or proc, a proc can be invoked like any other command\-simply by using its name. In any other namespace context, the proc is invoked using a qualified name like "\fIclassName\fB::\fIproc\fR". Procs in a base class that are redefined in the current class, or hidden by another base class, can also be accessed via their qualified name. .RE .TP \fBvariable \fIvarName\fR ?\fIinit\fR? ?\fIconfig\fR? . Defines an object-specific variable named \fIvarName\fR. All object-specific variables are automatically available in class methods. They need not be declared with anything like the \fBglobal\fR command. .RS .PP If the optional \fIinit\fR string is specified, it is used as the initial value of the variable when a new object is created. Initialization forces the variable to be a simple scalar value; uninitialized variables, on the other hand, can be set within the constructor and used as arrays. .PP The optional \fIconfig\fR script is only allowed for public variables. If specified, this code fragment is executed whenever a public variable is modified by the built-in "configure" method. The \fIconfig\fR script can also be specified outside of the class definition using the \fBconfigbody\fR command. .RE .TP \fBcommon \fIvarName\fR ?\fIinit\fR? . Declares a common variable named \fIvarName\fR. Common variables reside in the class namespace and are shared by all objects belonging to the class. They are just like global variables, except that they need not be declared with the usual \fBglobal\fR command. They are automatically visible in all class methods and procs. .RS .PP If the optional \fIinit\fR string is specified, it is used as the initial value of the variable. Initialization forces the variable to be a simple scalar value; uninitialized variables, on the other hand, can be set with subsequent \fBset\fR and \fBarray\fR commands and used as arrays. .PP Once a common data member has been defined, it can be set using \fBset\fR and \fBarray\fR commands within the class definition. This allows common data members to be initialized as arrays. For example: .PP .CS itcl::class Foo { common boolean set boolean(true) 1 set boolean(false) 0 } .CE .PP Note that if common data members are initialized within the constructor, they get initialized again and again whenever new objects are created. .RE .TP \fBpublic \fIcommand\fR ?\fIarg arg ...\fR? .TP \fBprotected \fIcommand\fR ?\fIarg arg ...\fR? .TP \fBprivate \fIcommand\fR ?\fIarg arg ...\fR? . These commands are used to set the protection level for class members that are created when \fIcommand\fR is evaluated. The \fIcommand\fR is usually \fBmethod\fR, \fBproc\fR, \fBvariable\fR or\fBcommon\fR, and the remaining \fIarg\fR's complete the member definition. However, \fIcommand\fR can also be a script containing many different member definitions, and the protection level will apply to all of the members that are created. .RE .SH "CLASS USAGE" .PP Once a class has been defined, the class name can be used as a command to create new objects belonging to the class. .TP \fIclassName objName\fR ?\fIargs...\fR? . Creates a new object in class \fIclassName\fR with the name \fIobjName\fR. Remaining arguments are passed to the constructor of the most-specific class. This in turn passes arguments to base class constructors before invoking its own body of commands. If construction is successful, a command called \fIobjName\fR is created in the current namespace context, and \fIobjName\fR is returned as the result of this operation. If an error is encountered during construction, the destructors are automatically invoked to free any resources that have been allocated, the object is deleted, and an error is returned. .RS .PP If \fIobjName\fR contains the string "\fB#auto\fR", that string is replaced with an automatically generated name. Names have the form \fIclassName<number>\fR, where the \fIclassName\fR part is modified to start with a lowercase letter. In class "Toaster", for example, the "\fB#auto\fR" specification would produce names like toaster0, toaster1, etc. Note that "\fB#auto\fR" can be also be buried within an object name: .PP .CS fileselectiondialog .foo.bar.#auto -background red .CE .PP This would generate an object named ".foo.bar.fileselectiondialog0". .RE .SH "OBJECT USAGE" .PP Once an object has been created, the object name can be used as a command to invoke methods that operate on the object. .TP \fIobjName method\fR ?\fIargs...\fR? . Invokes a method named \fImethod\fR on an object named \fIobjName\fR. Remaining arguments are passed to the argument list for the method. The method name can be "constructor", "destructor", any method name appearing in the class definition, or any of the following built-in methods. .SH "BUILT-IN METHODS" .TP \fIobjName \fBcget option\fR . Provides access to public variables as configuration options. This mimics the behavior of the usual "cget" operation for Tk widgets. The \fIoption\fR argument is a string of the form "\fB-\fIvarName\fR", and this method returns the current value of the public variable \fIvarName\fR. .TP \fIobjName \fBconfigure\fR ?\fIoption\fR? ?\fIvalue option value ...\fR? . Provides access to public variables as configuration options. This mimics the behavior of the usual "configure" operation for Tk widgets. With no arguments, this method returns a list of lists describing all of the public variables. Each list has three elements: the variable name, its initial value and its current value. .RS .PP If a single \fIoption\fR of the form "\fB-\fIvarName\fR" is specified, then this method returns the information for that one variable. .PP Otherwise, the arguments are treated as \fIoption\fR/\fIvalue\fR pairs assigning new values to public variables. Each variable is assigned its new value, and if it has any "config" code associated with it, it is executed in the context of the class where it was defined. If the "config" code generates an error, the variable is set back to its previous value, and the \fBconfigure\fR method returns an error. .RE .TP \fIobjName \fBisa \fIclassName\fR . Returns non-zero if the given \fIclassName\fR can be found in the object's heritage, and zero otherwise. .TP \fIobjName \fBinfo \fIoption\fR ?\fIargs...\fR? . Returns information related to a particular object named \fIobjName\fR, or to its class definition. The \fIoption\fR parameter includes the following things, as well as the options recognized by the usual Tcl "info" command: .RS .TP \fIobjName \fBinfo class\fR . Returns the name of the most-specific class for object \fIobjName\fR. .TP \fIobjName \fBinfo inherit\fR . Returns the list of base classes as they were defined in the "\fBinherit\fR" command, or an empty string if this class has no base classes. .TP \fIobjName \fBinfo heritage\fR . Returns the current class name and the entire list of base classes in the order that they are traversed for member lookup and object destruction. .TP \fIobjName \fBinfo function\fR ?\fIcmdName\fR? ?\fB-protection\fR? ?\fB-type\fR? ?\fB-name\fR? ?\fB-args\fR? ?\fB-body\fR? . With no arguments, this command returns a list of all class methods and procs. If \fIcmdName\fR is specified, it returns information for a specific method or proc. If no flags are specified, this command returns a list with the following elements: the protection level, the type (method/proc), the qualified name, the argument list and the body. Flags can be used to request specific elements from this list. .TP \fIobjName \fBinfo variable\fR ?\fIvarName\fR? ?\fB-protection\fR? ?\fB-type\fR? ?\fB-name\fR? ?\fB-init\fR? ?\fB-value\fR? ?\fB-config\fR? ?\fB-scope\fR? . With no arguments, this command returns a list of all object-specific variables and common data members. If \fIvarName\fR is specified, it returns information for a specific data member. Flags can be specified with \fIvarName\fR in an arbitrary order. The result is a list of the specific information in exactly the same order as the flags are specified. If no flags are given, this command returns a list as if the followings flags have been specified: .IP \fB-protection\fR \fB-type\fR \fB-name\fR \fB-init\fR \fB-value\fR ?\fB-config\fR? The \fB-config\fR result is only present if \fIvarName\fR is a public variable. It contains the code that is executed at initialization of \fIvarName\fR. The \fB-scope\fR flag gives the namespace context of \fIvarName\fR. Herewith the variable can be accessed from outside the object like any other variable. It is similar to the result of the \fBitcl::scope\fR command. .RE .SH "CHAINING METHODS/PROCS" .PP Sometimes a base class has a method or proc that is redefined with the same name in a derived class. This is a way of making the derived class handle the same operations as the base class, but with its own specialized behavior. For example, suppose we have a Toaster class that looks like this: .PP .CS itcl::class Toaster { variable crumbs 0 method toast {nslices} { if {$crumbs > 50} { error "== FIRE! FIRE! ==" } set crumbs [expr $crumbs+4*$nslices] } method clean {} { set crumbs 0 } } .CE .PP We might create another class like SmartToaster that redefines the "toast" method. If we want to access the base class method, we can qualify it with the base class name, to avoid ambiguity: .PP .CS itcl::class SmartToaster { inherit Toaster method toast {nslices} { if {$crumbs > 40} { clean } return [Toaster::toast $nslices] } } .CE .PP Instead of hard-coding the base class name, we can use the "chain" command like this: .PP .CS itcl::class SmartToaster { inherit Toaster method toast {nslices} { if {$crumbs > 40} { clean } return [chain $nslices] } } .CE .PP The chain command searches through the class hierarchy for a slightly more generic (base class) implementation of a method or proc, and invokes it with the specified arguments. It starts at the current class context and searches through base classes in the order that they are reported by the "info heritage" command. If another implementation is not found, this command does nothing and returns the null string. .SH "AUTO-LOADING" .PP Class definitions need not be loaded explicitly; they can be loaded as needed by the usual Tcl auto-loading facility. Each directory containing class definition files should have an accompanying "tclIndex" file. Each line in this file identifies a Tcl procedure or \fB[incr\ Tcl]\fR class definition and the file where the definition can be found. .PP For example, suppose a directory contains the definitions for classes "Toaster" and "SmartToaster". Then the "tclIndex" file for this directory would look like: .PP .CS # Tcl autoload index file, version 2.0 for [incr Tcl] # This file is generated by the "auto_mkindex" command # and sourced to set up indexing information for one or # more commands. Typically each line is a command that # sets an element in the auto_index array, where the # element name is the name of a command and the value is # a script that loads the command. set auto_index(::Toaster) "source $dir/Toaster.itcl" set auto_index(::SmartToaster) "source $dir/SmartToaster.itcl" .CE .PP The \fBauto_mkindex\fR command is used to automatically generate "tclIndex" files. .PP The auto-loader must be made aware of this directory by appending the directory name to the "auto_path" variable. When this is in place, classes will be auto-loaded as needed when used in an application. .SH "C PROCEDURES" .PP C procedures can be integrated into an \fB[incr\ Tcl]\fR class definition to implement methods, procs, and the "config" code for public variables. Any body that starts with "\fB@\fR" is treated as the symbolic name for a C procedure. .PP Symbolic names are established by registering procedures via \fBItcl_RegisterC()\fR. This is usually done in the \fBTcl_AppInit()\fR procedure, which is automatically called when the interpreter starts up. In the following example, the procedure \fCMy_FooCmd()\fR is registered with the symbolic name "foo". This procedure can be referenced in the \fBbody\fR command as "\fC@foo\fR". .PP .CS int Tcl_AppInit(interp) Tcl_Interp *interp; /* Interpreter for application. */ { if (Itcl_Init(interp) == TCL_ERROR) { return TCL_ERROR; } if (Itcl_RegisterC(interp, "foo", My_FooCmd) != TCL_OK) { return TCL_ERROR; } } .CE .PP C procedures are implemented just like ordinary Tcl commands. See the \fBCrtCommand\fR man page for details. Within the procedure, class data members can be accessed like ordinary variables using \fBTcl_SetVar()\fR, \fBTcl_GetVar()\fR, \fBTcl_TraceVar()\fR, etc. Class methods and procs can be executed like ordinary commands using \fBTcl_Eval()\fR. \fB[incr\ Tcl]\fR makes this possible by automatically setting up the context before executing the C procedure. .PP This scheme provides a natural migration path for code development. Classes can be developed quickly using Tcl code to implement the bodies. An entire application can be built and tested. When necessary, individual bodies can be implemented with C code to improve performance. .SH KEYWORDS class, object, object-oriented