Difference between revisions of "VJET/Typing Object Literals and Function References"

Revision as of 20:22, 14 February 2013

JavaScript object literals provide a way to define and create new objects.  They are also frequently used to define data structures and lightweight class instances.

Object Literals and Function References are frequently used constructs in JavaScript; they can be assigned to variables and properties, returned by functions, and passed as arguments.

In this example:

• Point is comprised of two Number properties
• Line is comprised of two Point properties
• Define the function SimpleLine that takes two Point arguments
• Define two function references: createLine and isSingularity

vjo.otype('Shape')
.defs ({
    Point: {
        x: undefined,   //< Number
        y: undefined    //< Number   
    },
    Line: {
        start: undefined,   //< Shape.Point
        end: undefined      //< Shape.Point
    },
 
    //> public Shape.Line createLine(Shape::Point pt1, Shape::Point pt2)
    createLine : vjo.NEEDS_IMPL,
 
    //> public boolean isSingularity(Shape.Line line)
    isSingularity: vjo.NEEDS_IMPL
 
})
.endType();

The vjo.NEEDS_IMPL is a placeholder object in that says that a Function is the value for this element.

When you need to refer to an otype definition from another type you must:

• Use the fully qualified name of the type, or use the .needs Comment, which serves as a shortcut to the otype namespace.
• Do not include the otype in a .needs section; otypes are not true types, but are used to provide a namespace for custom types.

The following example:

• Uses the needs Comment to create a shortcut for the otype namespace, samples.Shape
• Declares two Point properties and a Line property
• Declares a function typed as SimpleLine

vjo.ctype('samples.ConstructShape')
//> needs samples.Shape
.protos({
    point1 : {x:0, y:0},     //< Shape::Point
    point2 : {x:10, y:0},    //< Shape::Point
    line1 : undefined,       //< Shape::Line
 
    //> public Shape.SimpleLine createLine()
    createLine : function(pt1, pt2) {
        this.line1 = {start: pt1, end: pt2} ;
    }
})
.endType();