NAME

Joose.Manual.Traits - Special kind of Roles in Joose.

WHAT IS A TRAIT?

In Joose, a trait is almost exactly the same thing as a role, which is composed into an instance of a class at runtime to add or modify the behavior of just that instance. Other instances are not affected.

Any role can be used as a trait. There is no special Trait helper or other syntax constructs.

    Role('Logger', {

        requires : [ 'process' ],

        before : {
            process : function () {
                this.log("'process' method was called with the arguments:" + arguments)
            }
        },


        methods : {
            log : function () {
                ...
            }
        }
    })


    Class('Parser', {

        methods : {
            process : function () {
                ...
            }
        }
    })

APPLYING TRAIT. DETACHING

Traits can be applied only during object's instantiation. To apply the trait, provide the "pseudo-builder" trait (or traits) to class constructor:

    var parser = new Parser({
        trait : Logger
    })

Now this particular parser instance will perform additional loging during work. Note that any other instances of Parser will not be not affected.

You may also return the trait builder from the BUILD method (if you are using custom parameters processing).

Under the hood, the parser instance will have its own instance of metaclass, separated from Person:

    console.log(parser.meta != Parser.meta) // true, instance was detached
    console.log(parser instanceof Parser)   // true, its still Parser however )

You can extend this particular instance as usual class:

    parser.meta.extend({
        does : AnotherLogger
    })

If you don't want to apply trait during object's instantiation, but planning to do it later, you need to create it as detached. Use pseudo-builder detached for that:

    var parser = new Parser({
        detached : true
    })

    ...

    //later

    if (...) parser.meta.extend({
        does : Logger
    })

REMOVING TRAIT.

You may decide to remove the trait (rememeber, all Joose classes are mutable at run-time).

    parser.meta.extend({
        doesnot : Logger
    })

TRAITS AS META-ROLES

Sometime traits are also mentioned in meta-role context. This means, that this trait is being applied to the instance of meta-class. Such traits modifies the behaviour of class itself (its meta), not its methods or attributes.

An example of such trait can be a JooseX.Class.Singleton:

    Class('Some.Class', {
        trait : JooseX.Class.Singleton,

        has : {
            ...
        },

        methods : {
            ...
        }
    })

AUTHOR

Nickolay Platonov nickolay8@gmail.com

COPYRIGHT AND LICENSE

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