View source for VJET/Typing Object Literals and Function References

JavaScript object literals provide a way to define and create new objects.&nbsp; 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''

<source lang="javascript">
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();
</source> 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'', ''Shape'' 
*Declares two ''Point'' properties and a ''Line'' property 
*Declares a function that takes two ''Point'''s and returns a ''Line'' 
*Declares a function that take a ''Line'' and returns a boolean

<source lang="javascript">
vjo.ctype('MyShape')
//> needs Shape
.protos({
    point1 : {x:0, y:0},     //< Shape:Point
    point2 : {x:10, y:0},    //< Shape:Point
 
    //> public Shape.Line createLine(Shape:Point pt1, Shape:Point pt2)
    createLine : function(pt1, pt2) {
    	this.point1 = pt1 ;
    	this.point2 = pt2 ;
    	return {start: pt1, end: pt2} ;
    },
    
    //> public boolean isSingularity(Shape:Line line) 
    isSingularity: function(line) {
		return line.start.x == 0 
			&& line.start.y == 0
			&& line.end.x == 0
			&& line.end.y == 0 ;
    }
})
.endType();
</source> 

It is important to note that we can use our VJET types in freeform Javascript as well <source lang="javascript">
//> Shape:Point
var point1 = {x:0, y: 0};
 
//> Shape:Point
var point2 = {x:10, y:20};
 
//> Shape.Line createLine(Shape:Point pt1, Shape:Point pt2)
function createLine(pt1, pt2) {
	point1 = pt1 ;
	point2 = pt2 ;
    return {start: pt1, end: pt2};
}

//> boolean isSingularity(Shape:Line line)
function isSingularity(line) {
	return line.start.x == 0 
		&& line.start.y == 0
		&& line.end.x == 0
		&& line.end.y == 0 		
}

var line1 = createLine(point1, point2) ;
var line2 = createLine(point1, point1) ; // is the singularity

var out = vjo.sysout.println ; // Will output to the Eclipse console

out("line1 singularity: " + isSingularity(line1)) ;
out("line2 singularity: " + isSingularity(line2)) ;
</source> 

[[Category:VJET]] [[Category:VJO]]