Traits

A trait is a construct that lets you use code again and again. In a language that does not let classes inherit from more than one parent class, such as ViviFire, traits can decrease some of the limits this causes. Traits let you use sets of methods freely in different classes, related or not. The effects of the mixture of traits and classes are specified in a manner which is easy to accept.

A trait shows almost the same as a class, but specifies only behavior in a controlled manner. You cannot make a variable from a trait. Together with the usual inheritance construct, traits do what is known as horizontal composition of behavior. That is, the trait applies its methods to a class without inheritance.

Declaration of traits

A trait usually starts with Trait and completes with End Trait. Between these two lines you can put one or more permitted statements: Method, Property, Function, Sub, and TBD.

A class that uses a trait has access only to the public members of the trait—methods and properties. These also become part of the interface of the class . The class cannot directly get access to the other members of the trait.

A method or property is usually made with a body of statements. But if you use the modifier @Abstract, then the method or property cannot have a body. A class that uses the trait must declare the method or property again, and supply a body of statements.

Precedence

If a class and a trait make available different methods with the same signature, then the class comes before the trait. And if a trait and a parent class cause the same problem, then the trait comes before the parent class.

That is, class > trait > parent class.

Multiple traits

TODO

Conflict resolution

Trait A
    Method Calculate
        ' ...
    End Method
End Trait

Trait B
    Method Calculate
        ' ...
    End Method
End Trait

Class Calculator Does A Does B
    Method CalculateA Does A.Calculate
    Method CalculateB Does B.Calculate
End Class

To Change method visibility

Trait Foobar
    Method Foo
        ' ...
    End Method
    Method Bar
        ' ...
    End Method
End Trait

Class Barless Does Foobar
    Function Bar Does Foobar.Bar
End Class

Traits composed from traits

Trait Foo
    Method Foo
        ' ...
    End Method
End Trait

Trait Bar
    Method Bar
        ' ...
    End Method
End Trait

Trait Foobar Does Foo Does Bar
    ' ...
End Trait

Abstract traits

If all of the methods and properties of a trait must be abstract, then you can put @Abstract before the trait. Then it is not necessary to put the modifier before each method and property.

An abstract trait has more limits than a usual trait:

Shared trait members

TODO

Properties

TODO

Uses for traits

TODO

Examples

@Abstract Class Pet
End Class

Trait Walk
    Method StartWalking
    End Method
End Trait

Trait Swim
    Method StartSwimming
    End Method
End Trait

@Abstract Trait Speak
    Method Speak As String
End Trait

Class Dog Is Pet Does Walk Does Swim Does Speak
    @Override Method Speak As String
        Return "Arf"
    End Method
End Class

Class Cat Is Pet Does Walk Does Speak
    @Override Method Speak As String
        Return "Meow"
    End Method
End Class

Class Fish Is Pet Does Swim
End Class

See also