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easejs/lib/class_abstract.js

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/**
* Wrapper permitting the definition of abstract classes
*
* This doesn't actually introduce any new functionality. Rather, it sets a
* flag to allow abstract methods within a class, forcing users to clearly
* state that a class is abstract.
*
* Copyright (C) 2010, 2011, 2013, 2014 Free Software Foundation, Inc.
*
* This file is part of GNU ease.js.
*
* ease.js is free software: you can redistribute it and/or modify
* it under the terms of the GNU 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
var Class = require( __dirname + '/class' );
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/**
* Creates an abstract class
*
* @return {Function} abstract class
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*/
module.exports = exports = function()
{
markAbstract( arguments );
// forward everything to Class
var result = Class.apply( this, arguments );
// if we're using the temporary object, then override its methods to permit
// abstract classes
if ( !Class.isClass( result ) )
{
abstractOverride( result );
}
return result;
};
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/**
* Creates an abstract class from a class extend operation
*
* @return {Function} abstract class
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*/
exports.extend = function()
{
markAbstract( arguments );
return Class.extend.apply( this, arguments );
};
/**
* Mixes in a trait
*
* @return {Object} staged abstract class
*/
exports.use = function()
{
return abstractOverride(
Class.use.apply( this, arguments )
);
};
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/**
* Creates an abstract class implementing the given members
*
* Simply wraps the class module's implement() method.
*
* @return {Object} staged abstract class
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*/
exports.implement = function()
{
return abstractOverride(
Class.implement.apply( this, arguments )
);
};
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/**
* Causes a definition to be flagged as abstract
*
* This function assumes the last argument to be the definition, which is the
* common case, and modifies the object referenced by that argument.
*
* @param {Arguments} args arguments to parse
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*
* @return {undefined}
*/
function markAbstract( args )
{
// the last argument _should_ be the definition
var dfn = args[ args.length - 1 ];
if ( typeof dfn === 'object' )
{
// mark as abstract
dfn.___$$abstract$$ = true;
}
}
/**
* Overrides object members to permit abstract classes
*
* @param {Object} obj object to override
*
* @return {Object} obj
*/
function abstractOverride( obj )
{
var extend = obj.extend,
impl = obj.implement,
use = obj.use;
// wrap and apply the abstract flag, only if the method is defined (it
// may not be under all circumstances, e.g. after an implement())
impl && ( obj.implement = function()
{
return abstractOverride( impl.apply( this, arguments ) );
} );
var mixin = false;
use && ( obj.use = function()
{
return abstractOverride( use.apply( this, arguments ) );
} );
// wrap extend, applying the abstract flag
obj.extend = function()
{
markAbstract( arguments );
return extend.apply( this, arguments );
};
// used by mixins; we need to mark the intermediate subtype as abstract,
// but ensure we don't throw any errors if no abstract members are mixed
// in (since thay may be mixed in later on)
obj.__createBase = function()
{
return extend( { ___$$auto$abstract$$: true } );
};
return obj;
}