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easejs/lib/class.js

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/**
* Contains basic inheritance mechanism
*
* Copyright (C) 2010 Mike Gerwitz
*
* This file is part of ease.js.
*
* ease.js is free software: you can redistribute it and/or modify it under the
* terms of the GNU Lesser General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* @author Mike Gerwitz
* @package core
*/
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// whether getters/setters are supported
var getset = ( Object.prototype.__defineGetter__ === undefined )
? false
: true
;
/**
* Creates a class, inheriting either from the provided base class or the
* default base class
*
* @param {Object} base object to extend (extends Class by default)
*
* @return {Object} extended class
*/
exports.extend = function( base )
{
return extend.apply( this, arguments );
}
/**
* Default class implementation
*
* @return undefined
*/
function Class() {};
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/**
* Copies properties to the destination object
*
* If the method already exists, it will be overridden and accessible via either
* the parent prototype or by invoking this.__super().
*
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* The destination object is directly modified.
*
* @param {Object} props properties to copy
* @param {Object} dest destination object
*
* @return undefined
*/
function prop_copy( props, dest )
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{
// copy each of the properties to the destination object
for ( property in props )
{
// if the property already exists, then it's being overridden (we only
// care about methods - properties will simply have their values
// overwritten)
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var pre = dest[ property ],
prop = props[ property ],
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getter = ( ( getset ) ? props.__lookupGetter__( property ) : null ),
setter = ( ( getset ) ? props.__lookupSetter__( property ) : null );
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// check for getter/setter overrides
if ( getter || setter )
{
if ( getter )
{
dest.__defineGetter__( property, getter );
}
if ( setter )
{
dest.__defineSetter__( property, setter );
}
}
// check for method overrides
else if ( ( pre !== undefined ) && ( pre instanceof Function ) )
{
// ensure we're overriding the method with another method
if ( !( prop instanceof Function ) )
{
throw new TypeError( "Cannot override method with non-method" );
}
dest[ property ] = ( function( method, super_method )
{
// this is the method that will be invoked when the requested
// method is called, so note that in the context of this
// function, `this` will represent the current class instance
return function()
{
var tmp = this.__super;
// assign _super temporarily for the method invocation so
// that the method can call the parent method
this.__super = super_method;
var retval = method.apply( this, arguments );
this.__super = tmp;
return retval;
}
})( prop, dest[ property ] );
}
else
{
dest[ property ] = prop;
}
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}
}
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/**
* Mimics class inheritance
*
* This method will mimic inheritance by setting up the prototype with the
* provided base class (or, by default, Class) and copying the additional
* properties atop of it.
*
* The class to inherit from (the first argument) is optional. If omitted, the
* first argument will be considered to be the properties list.
*
* @return {Object} extended class
*/
function extend()
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{
var args = Array.prototype.slice.call( arguments ),
props = args.pop() || {},
base = args.pop() || Class,
prototype = new base(),
new_class = function()
{
if ( this.__construct instanceof Function )
{
this.__construct.apply( this, arguments );
}
};
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// copy the given properties into the new prototype
prop_copy( props, prototype );
// reference to the parent prototype (for more experienced users)
prototype.parent = base.prototype;
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// set up the new class
attach_extend( new_class );
new_class.prototype = prototype;
new_class.constructor = new_class;
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return new_class;
}
/**
* Attaches extend method to the given function's prototype
*
* @param {Function} func function to attach method to
*
* @return undefined
*/
function attach_extend( func )
{
/**
* Shorthand for extending classes
*
* This method can be invoked on the object, rater than having to call
* Class.extend( this ).
*
* @param {Object} props properties to add to extended class
*
* @return {Object} extended class
*/
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var ext_method = function( props )
{
return extend( this, props );
};
// if defineProperty is unsupported, do it the old fashioned way (it's just
// less restrictive)
if ( Object.defineProperty === undefined )
{
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func.extend = ext_method;
}
else
{
Object.defineProperty( func, 'extend',
{
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value: ext_method,
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enumerable: false,
writable: false,
configurable: false,
} );
}
}