forked from hummypkg/webif
373 lines
12 KiB
HTML
373 lines
12 KiB
HTML
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<!DOCTYPE HTML>
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<html lang="en">
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<head>
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<meta charset="utf-8">
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<title>Jim Tcl - Object Oriented</title>
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<meta name="generator" content="nanoc 3.1.6">
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</head>
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<body>
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<div id="header">
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<h1 id="blog-title">The Jim Interpreter</h1>
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<p id="description">A small footprint implementation of the Tcl programming language</p>
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</div>
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<div id="content">
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<div class="breadcrumbs">
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<a href="/">The Jim Interpreter</a>
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»
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<a href="/documentation/">Documentation</a>
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»
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<a href="/documentation/oo/">Object Oriented</a>
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</div>
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<div class="main" id="main">
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<h1 id="object-oriented-support-for-jim-tcl">Object Oriented Support for Jim Tcl</h1>
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<h2 id="overview">OVERVIEW</h2>
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<p>The pure-Tcl oo package leverages Jim’s unique strengths
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to provide support for Object Oriented programming. </p>
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<p>The oo package can be statically linked with Jim or installed
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as a separate Tcl package and loaded with:</p>
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<pre class="sh_tcl">
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package require oo
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</pre>
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<h2 id="declaring-classes">DECLARING CLASSES</h2>
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<p>A class is declared with the <code>class</code> proc as follows.</p>
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<pre class="sh_tcl">
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class myclass ?baseclasses? classvars
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</pre>
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<p>This declares a class named <code>myclass</code> with the given dictionary,
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<code>classvars</code>, providing the initial state of all new objects.
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It is important to list all class variables in <code>classvars</code>, even
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if initialised only to the empty string, since the class makes
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these variables available in methods and via <code>[myclass vars]</code>.</p>
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<p>A list of zero or more base classes may also be specified from
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which methods and class variables are imported. See INHERITANCE
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below for more details.</p>
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<p>Declaring a class creates a procedure with the class name along
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with some related procedures. For example:</p>
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<pre class="sh_tcl">
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. class Account {balance 0}
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Account
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. info procs Account*
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{Account get} {Account methods} {Account eval} Account {Account new} {Account destroy}
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{Account vars} {Account classname} {Account classvars} {Account method}
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</pre>
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<p>Notice that apart from the main <code>Account</code> procedure, all the remaining procedures (methods)
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are prefixed with <code>Account</code> and a space.</p>
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<h2 id="predefined-class-methods">PREDEFINED CLASS METHODS</h2>
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<p>Decaring a class pre-defines a number of “class” methods. i.e. those which don’t
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require an object and simply return or manipulate properties of the class. These are:</p>
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<dl>
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<dt><strong>new</strong> ?instancevars?</dt>
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<dd>Creates and returns new object, optionally overriding the default class variable values.
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Note that the class name is an alias for <code>classname new {}</code> and can be used as a shorthand
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for creating new objects with default values.</dd>
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</dl>
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<dl>
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<dt><strong>method</strong> name arglist body</dt>
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<dd>Creates or redefines a method for the class with the given name, argument list and body.</dd>
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</dl>
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<dl>
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<dt><strong>methods</strong></dt>
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<dd>Returns a list of the methods supported by this class, including both class methods
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and instance methods. Also includes base class methods.</dd>
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</dl>
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<dl>
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<dt><strong>vars</strong></dt>
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<dd>Returns a list of the class variables for this class (names
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only). Also includes base class variables.</dd>
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</dl>
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<dl>
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<dt><strong>classvars</strong></dt>
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<dd>Returns a dictionary the class variables, including initial values, for this class.
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Also includes base class variables.</dd>
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</dl>
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<dl>
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<dt><strong>classname</strong></dt>
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<dd>Returns the classname. This can be useful as [$self classname].</dd>
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</dl>
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<p>Class methods may be invoked either via the class name or via an object of the class.
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For example:</p>
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<pre class="sh_tcl">
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. class Account {balance 0}
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Account
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. Account methods
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classname classvars destroy eval get method methods new vars
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. set a [Account]
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<reference.<Account>.00000000000000000001>
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. $a methods
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classname classvars destroy eval get method methods new vars
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</pre>
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<h2 id="predefined-object-methods">PREDEFINED OBJECT METHODS</h2>
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<p>Decaring a class pre-defines a number of “object” methods. i.e. those which operate
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on a specific object.</p>
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<dl>
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<dt><strong>destroy</strong></dt>
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<dd>Destroys the object. This method may be overridden, but note that it should
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delete the object with {rename $self “”}. This method will also be called
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if the object is reaped during garbage collection.</dd>
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</dl>
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<dl>
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<dt><strong>get</strong> varname</dt>
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<dd>Returns the value of the given instance variable.</dd>
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</dl>
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<dl>
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<dt><strong>eval</strong> ?locals? body</dt>
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<dd>Makes any given local variables available to the body, along with
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the instance variables, and evaluate the body in that context.
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This can be used for one-off evaluation to avoid declaring a method.</dd>
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</dl>
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<h2 id="creating-objects">CREATING OBJECTS</h2>
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<p>An object is created with the <code>new</code> method, or simply by using the classname shortcut.
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If the <code>new</code> method is used, the variables for the newly created object (instance variables)
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may be initialised. Otherwise they are set to the default values specified when the
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class was declared.</p>
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<p>For example:</p>
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<pre class="sh_tcl">
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. class Account {balance 0}
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Account
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. set a [Account]
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<reference.<Account>.00000000000000000001>
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. set b [Account new {balance 1000}]
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<reference.<Account>.00000000000000000002>
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. $a get balance
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0
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. $b get balance
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1000
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</pre>
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<h2 id="declaring-methods">DECLARING METHODS</h2>
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<p>In addition to the predefined methods, new methods may be decared, or existing
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methods redefined with the class method, method.</p>
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<p>Declaring a method is very similar to defining a proc, and the arglist
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has identical syntax. For example:</p>
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<pre class="sh_tcl">
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. Account method show {{chan stdout}} { $chan puts "Balance of account is $balance" }
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. $b show
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Balance of account is 1000
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</pre>
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<p>All instance variables are available within the method and any
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changes to these variables are maintained by the object.</p>
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<p>In addition, the $self variables is defined and refers to the current object.
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This may be used to invoke further methods on the object. For example:</p>
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<pre class="sh_tcl">
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. Account method show {} { puts "Balance of account is [$self get balance]" }
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. $b show
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Balance of account is 1000
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</pre>
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<p>Notes:</p>
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<ul>
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<li>It is a bad idea to unset an instance variable.</li>
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<li>In general, you should avoid redefining any of the pre-defined methods, except for <code>destroy</code>.</li>
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<li>When accessing the caller’s scope with upvar or uplevel, note that there
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are two frame levels between the caller and the method. Thus it is necessary
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to use <code>upvar 2</code> or <code>uplevel 2</code></li>
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</ul>
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<h2 id="inheritance">INHERITANCE</h2>
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<p>For each base class given in a new class declaration, the methods
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and variables of those classes are imported into the new class being
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defined. Base classes are imported in left to right order, so that if a
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method is defined in more than one base class, the later definition
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is selected. This applies similarly to class variables.</p>
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<p>Within a method, <code>super</code> may be used to explicitly invoke a
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base class method on the object. This applies only to the <em>last</em>
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base class given. For example:</p>
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<pre class="sh_tcl">
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# Assumes the existence of classes Account and Client
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. Account method debit {amount} { incr balance -$amount }
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. class CreditAccount {Client Account} {type visa}
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CreditAccount
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. CreditAccount method debit {amount} {
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puts "Debit $type card"
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super debit $amount
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}
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. set a [CreditAccount]
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<reference.<Account>.00000000000000000001>
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. $a debit 20
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Debit visa card
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. $a balance
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-20
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</pre>
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<p>In the CreditAccount debit method, the call to <code>super debit</code> invokes
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the method <code>Account debit</code> since Account is the last base class listed.</p>
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<h2 id="object-lifetimegarbage-collection">OBJECT LIFETIME/GARBAGE COLLECTION</h2>
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<p>Objects are implemented as lambdas. That is, they are procedures with state
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and are named as references. This means that when an object is no longer
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reachable by any name and garbage collection runs, the object will be
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discarded and the destructor will be invoked. Note that the garbage collector
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can be invoked manually with <code>collect</code> if required.</p>
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<pre class="sh_tcl">
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. class Account {}
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Account
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. Account method destroy {} { puts dying...; rename $self "" }
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Account destroy
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. proc a {} { set b [Account]; return "" }
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a
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. a
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. collect
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dying...
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1
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</pre>
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<h2 id="class-methodsclass-static-variables">CLASS METHODS/CLASS STATIC VARIABLES</h2>
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<p>All methods defined with <code>method</code> operate on objects (instances).
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If a class method is required, it is possible to simply declare one with <code>proc</code>.
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The method dispatcher will automatically be able to dispatch to this method.
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Using this approach, it is also possible to add class static variables by
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defining static variables to the proc. Although strictly these variables
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are accessible only to that proc, not the class as a whole.</p>
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<p>For example:</p>
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<pre class="sh_tcl">
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. class Account {}
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Account
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. proc {Account nextid} {} {{id 0}} { incr id }
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Account nextid
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. Account nextid
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1
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. Account nextid
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2
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. set a [Account]
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<reference.<Account>.00000000000000000001>
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. $a nextid
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3
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. $a eval { $self nextid }
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4
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</pre>
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<h2 id="how-method-dispatch-works">HOW METHOD DISPATCH WORKS</h2>
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<p>All class and object methods are name “classname methodname”.</p>
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<p>The class method dispatcher is named “classname”. When invoked with a methodname,
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it simply invokes the method “classname methodname”.</p>
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<p>The method dispatch is via a two step process. Firstly the object procedure is invoked
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with the method name. This procedure then invokes “classname method” which sets up
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the appropriate access to the object variables, and then invokes the method body.</p>
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<h2 id="examples">EXAMPLES</h2>
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<h3 id="treetclhttprepoorczwjimtclgitblobheadtreetcl"><a href="http://repo.or.cz/w/jimtcl.git/blob/HEAD:/tree.tcl">tree.tcl</a></h3>
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<p>The <code>tree</code> package is implemented using the <code>oo</code> package.
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See the source code in tree.tcl and a usage example in tests/tree.test</p>
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<p>Of particular note is how callbacks and recursive invocation is used in the <code>walk</code> method.</p>
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<h3 id="examplesootesttclhttprepoorczwjimtclgitblobheadexamplesootesttcl"><a href="http://repo.or.cz/w/jimtcl.git/blob/HEAD:/examples/ootest.tcl">examples/ootest.tcl</a></h3>
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<p>A comprehensive OO example is provided in examples/ootest.tcl.</p>
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<p>It can be run simply as:</p>
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<pre class="sh_unix">
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$ ./jimsh examples/ootest.tcl
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</pre>
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</div>
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</div>
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<div id="sidebar">
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<h2>About Jim Tcl</h2>
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<ul>
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<li class="stdlink"><a href="/">Introduction</a></li>
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<li class="newlink"><a href="/news/">News</a></li>
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<li class="stdlink"><a href="/download/">Download</a></li>
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<li class="stdlink"><a href="/documentation/">Documentation</a></li>
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<li class="stdlink"><a href="/extensions/">Extensions</a></li>
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<li class="stdlink"><a href="/license/">License</a></li>
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<li class="stdlink"><a href="/about/">About</a></li>
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</ul>
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<h2>Community</h2>
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<ul>
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<li><a href="https://lists.berlios.de/mailman/listinfo/jim-devel">Mailing List</a></li>
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<li><a href="https://github.com/msteveb/jimtcl">Jim on github</a></li>
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<li><a href="http://wiki.tcl.tk/jim">Jim @ the Tcler's Wiki</a></li>
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<li><a href="http://developer.berlios.de/projects/jim">Berlios Project Page</a></li>
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</ul>
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