Correct trait->class calling context on class supertype
See test cases for more information. This was a pretty unfortunate and nasty bug that I discovered while working on a project that uses easejs; it wasn't something that was found previously because this support was only added relatively recently, and this problem does not exist if an interface is used. * lib/Trait.js (bindSuperCtx): Add function. (tctor): Use it. * test/Trait/ScopeTest.js: Add calling context tests.master
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748ceaf0bf
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04e98e682e
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lib/Trait.js
32
lib/Trait.js
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@ -908,6 +908,10 @@ function tctor( tc, base, privsym )
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// the intimate relationship
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this[ f ] = C( base, this[ privsym ].vis )[ privsym ].vis;
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// rebind trait's supertype context (if any) to our own, causing us
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// to share state
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bindSuperCtx( this[ f ], this, privsym );
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// this has been previously validated to ensure that it is a
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// function
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this[ f ].__mixin && this[ f ].__mixin.apply(
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@ -920,6 +924,34 @@ function tctor( tc, base, privsym )
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};
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/**
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* Bind the supertype context to that of another instance
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*
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* The source instance FROM is expected to have a `___$$super$$' property
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* holding a reference to the supertype. The context associated with the
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* supertype's class id X in FROM will then be reassigned by reference to
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* the context X of instance TO.
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*
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* This has the effect of ensuring that, whenever a call enters the
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* supertype's context in FROM, it will use all state from the context of
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* TO. For mixins, this means that---despite the trait itself inheriting
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* from the class---we will use the private state of the _mixer_, not our
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* own.
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*
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* This is all done without any loss in performance, since calling context
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* is immediately bound rather than resolved during each method call.
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*
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* TODO: make into a standard API for class manipulation
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*/
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function bindSuperCtx( from, to, privsym )
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{
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var ctx = from[ privsym ].vis,
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cid = ctx.___$$super$$.__cid;
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ctx[ privsym ].vis[ cid ] = to[ privsym ].vis[ cid ];
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}
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/**
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* Create trait constructor
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*
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@ -17,14 +17,19 @@
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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* These tests could possibly duplicate tests elsewhere; that's fine, as
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* this is a vital concept that wouldn't hurt to be reiterated in a
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* different context (no pun intended).
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*/
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require( 'common' ).testCase(
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{
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caseSetUp: function()
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{
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this.Sut = this.require( 'Trait' );
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this.Class = this.require( 'class' );
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this.Sut = this.require( 'Trait' );
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this.Class = this.require( 'class' );
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this.Interface = this.require( 'interface' );
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},
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@ -149,4 +154,218 @@ require( 'common' ).testCase(
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} )().callFoo();
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} );
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},
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/**
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* When a class makes a call to a trait method, the calling context
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* should be that of the trait itself (that is, the trait has its own
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* internal state).
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*/
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'Class->trait calling context binds to trait': function()
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{
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var T = this.Sut(
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{
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'private _foo': [],
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_givenMixin: null,
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// must be properly bound before mixin
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__mixin: function()
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{
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this._givenMixin = this.get();
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},
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push: function( item )
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{
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this._foo.push( item );
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},
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// make sure calling context is preserved on override
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'virtual overridePush': function( item )
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{
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this._foo.push( item );
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},
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get: function()
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{
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return this._foo;
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},
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getGivenMixin: function()
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{
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return this._givenMixin;
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},
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} );
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var inst = this.Class.use( T ).extend(
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{
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// ensure calling context on T
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superPush: function( item )
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{
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this.push( item );
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},
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'override overridePush': function( item )
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{
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this.__super( item );
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},
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} )();
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inst.push( 'a' );
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inst.superPush( 'b' );
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inst.overridePush( 'c' );
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this.assertDeepEqual( [ 'a', 'b', 'c' ], inst.get() );
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this.assertStrictEqual( inst.get(), inst.getGivenMixin() );
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},
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/**
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* This test focuses on an implementation detail: that traits extending
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* classes literally extend that class. The problem there is that,
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* because of this detail, calling one of the supertypes methods is
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* going to apply the method within the context of _that
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* trait_. Remember: each object has private state associated with each
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* class in its hierarchy. So the class C containing the mixin of trait
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* T has it's own state S_c, and T has its own state T_c because of the
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* extension. Given C#Foo, calling T#Foo applies T_c rather than the
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* intended C_c. That is, without proper care.
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*
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* This tests to make sure the context has been properly rebound to the
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* mixer.
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*/
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'Trait->class calling context binds to class': function()
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{
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var C = this.Class(
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{
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'private _stack': [],
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'virtual push': function( item )
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{
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this._stack.push( item );
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},
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// non-virtual, test fall-through
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getStack: function()
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{
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return this._stack;
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},
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} );
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var T = this.Sut.extend( C,
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{
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_givenMixin: null,
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// proper context set before __mixin
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__mixin: function()
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{
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this._givenMixin = this.getStack();
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},
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// proper context to __super
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'override push': function( item )
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{
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this.__super( item );
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},
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// proper context to parent `getStack'
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getSuperStack: function()
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{
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return this.getStack();
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},
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getGivenMixin: function()
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{
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return this._givenMixin;
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},
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} );
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var stack = C.use( T )();
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stack.push( 'a' );
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// proper context to parent method call (non-__super)
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this.assertStrictEqual( stack.getStack(), stack.getSuperStack() );
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// proper context to __super
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this.assertDeepEqual( [ 'a' ], stack.getStack() );
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// context available before __mixin
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this.assertStrictEqual( stack.getStack(), stack.getGivenMixin() );
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},
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/**
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* Similar to the above, except that we extend an interface rather than
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* a base class.
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*
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* Notice how T here implements I rather than extending C, and
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* consequently uses `abstract override' in place of `override'.
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*
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* What is interesting in this case is whether this test fails when the
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* previous does not, or vice-versa (such was the case when this test
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* was introduced).
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*/
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'Trait->interface calling context binds to implementing class': function()
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{
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var I = this.Interface(
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{
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push: [ 'item' ],
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getStack: [],
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} );
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var C = this.Class.implement( I ).extend(
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{
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'private _stack': [],
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'virtual push': function( item )
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{
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this._stack.push( item );
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},
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// non-virtual, test fall-through
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getStack: function()
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{
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return this._stack;
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},
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} );
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var T = this.Sut.implement( I ).extend(
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{
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_givenMixin: null,
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// proper context set before __mixin
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__mixin: function()
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{
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this._givenMixin = this.getStack();
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},
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// proper context to __super
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'abstract override push': function( item )
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{
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this.__super( item );
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},
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// proper context to parent `getStack'
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getSuperStack: function()
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{
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return this.getStack();
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},
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getGivenMixin: function()
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{
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return this._givenMixin;
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},
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} );
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var stack = C.use( T )();
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stack.push( 'a' );
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// proper context to parent method call (non-__super)
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this.assertStrictEqual( stack.getStack(), stack.getSuperStack() );
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// proper context to __super
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this.assertDeepEqual( [ 'a' ], stack.getStack() );
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// context available before __mixin
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this.assertStrictEqual( stack.getStack(), stack.getGivenMixin() );
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},
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} );
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