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easejs/lib/propobj.js

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/**
* Contains property object generator
*
* 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
*/
var util = require( __dirname + '/util' ),
// whether or not we support defining properties through
// Object.defineProperty()
defprop = !( util.definePropertyFallback() );
;
/**
* Sets up properties (non-inheriting)
*
* This includes all members (including private). Private members will be set up
* in a separate object, so that they can be easily removed from the mix. That
* object will include the destination object in the prototype, so that the
* access should be transparent. This object is returned.
*
* Properties are expected in the following format. Note that keywords are
* ignored:
* { public: { prop: [ value, { keyword: true } ] } }
*
* @param {Object} dest destination object
* @param {Object} properties properties to copy
* @param {Object=} methods methods to copy
*
* @return {Object} object containing private members and dest as prototype
*/
exports.setup = function( dest, properties, methods )
{
var obj = dest;
// this constructor is an extra layer atop of the destination object, which
// will contain the private methods
if ( defprop )
{
var obj_ctor = function() {};
obj_ctor.prototype = dest;
obj = new obj_ctor();
// all private protected proxies need to be proxied from the private
// object (which will be passed as the context) to the object containing
// protected values
exports.createPropProxy( dest, obj, properties[ 'protected' ] );
}
// initialize each of the properties for this instance to
// ensure we're not sharing references to prototype values
doSetup( dest, properties[ 'public' ] );
// Do the same for protected, but only if they do not exist already in
// public. The reason for this is because the property object is laid /atop/
// of the public members, meaning that a parent's protected members will
// take precedence over a subtype's overriding /public/ members. Uh oh.
doSetup( dest,
properties[ 'protected' ],
methods[ 'protected' ],
'public'
);
// then add the private parts
doSetup( obj, properties[ 'private' ], methods[ 'private' ] );
return obj;
};
/**
* Set up destination object by copying over properties and methods
*
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* @param {Object} dest destination object
* @param {Object} properties properties to copy
* @param {Object=} methods methods to copy
* @param {boolean} unless_keyword do not set if keyword is set on existing
* method
*
* @return {undefined}
*/
function doSetup( dest, properties, methods, unless_keyword )
{
var hasOwn = Array.prototype.hasOwnProperty,
pre = null;
// copy over the methods
if ( methods !== undefined )
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{
for ( method_name in methods )
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{
if ( hasOwn.call( methods, method_name ) )
{
pre = dest[ method_name ];
// If requested, do not copy the method over if it already
// exists in the destination object. Don't use hasOwn here;
// unnecessary overhead and we want to traverse any prototype
// chains. We do not check the public object directly, for
// example, because we need a solution that will work if a proxy
// is unsupported by the engine.
//
// Also note that we need to allow overriding if it exists in
// the protected object (we can override protected with
// protected). This is the *last* check to ensure a performance
// hit is incured *only* if we're overriding protected with
// protected.
if ( !unless_keyword
|| ( pre === undefined )
|| !( pre.___$$keywords$$[ unless_keyword ] )
)
{
dest[ method_name ] = methods[ method_name ];
}
}
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}
}
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// initialize private/protected properties and store in instance data
for ( prop in properties )
{
if ( hasOwn.call( properties, prop ) )
{
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dest[ prop ] = util.clone( properties[ prop ][ 0 ] );
}
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}
}
/**
* Creates a proxy for all given properties to the given base
*
* The proxy uses getters/setters to forward all calls to the base. The
* destination object will be used as the proxy. All properties within props
* will be used proxied.
*
* To summarize: for each property in props, all gets and sets will be forwarded
* to base.
*
* @param {Object} base object to proxy to
* @param {Object} dest object to treat as proxy (set getters/setters on)
* @param {Object} props properties to proxy
*
* @return {Object} returns dest
*/
exports.createPropProxy = function( base, dest, props )
{
var hasOwn = Object.prototype.hasOwnProperty;
if ( !defprop )
{
return base;
}
for ( prop in props )
{
if ( !( hasOwn.call( props, prop ) ) )
{
continue;
}
( function( prop )
{
// just in case it's already defined, so we don't throw an error
dest[ prop ] = undefined;
// public properties, when set internally, must forward to the
// actual variable
Object.defineProperty( dest, prop, {
set: function( val )
{
base[ prop ] = val;
},
get: function()
{
return base[ prop ];
},
enumerable: true,
} );
} ).call( null, prop );
}
return dest;
};
/**
* Returns whether property proxying is supported
*
* Proxying is done via getters and setters. If the JS engine doesn't support
* them (pre-ES5), then the proxy will not work.
*
* @return {boolean} true if supported, otherwise false
*/
exports.supportsPropProxy = function()
{
return defprop;
};