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Formula

History
ReleaseChanges
17 R6Renamed (New formula -> Formula)
17 R3Added

Formula ( formulaExp : Expression ) : 4D.Function

ParameterTypeDescription
formulaExpExpression→Formula to be returned as object
Result4D.Function←Native function encapsulating the formula

Description​

The Formula command creates a 4D Function object based upon the formulaExp expression. formulaExp can be as simple as a single value or complex, such as a project method with parameters.

Having a formula as an object allows it to be passed as a parameter (calculated attribute) to commands or methods or to be executed from various components without needing to declare them as "shared by components and host database". When called, the formula object is evaluated within the context of the database or component that created it.

The returned formula can be called with:

 var $f : 4D.Function
 $f:=Formula(1+2)
 $o:=New object("myFormula";$f)

  //three different ways to call the formula
 $f.call($o) //returns 3
 $f.apply($o) //returns 3
 $o.myFormula() //returns 3

You can pass parameters to the Formula, as seen below in example 4.

You can specify the object on which the formula is executed, as seen in example 5. The properties of the object can then be accessed via the This command.

If formulaExp uses local variables, their values are copied and stored in the returned formula object when it is created. When executed, the formula uses these copied values rather than the current value of the local variables. Note that using arrays as local variables is not supported.

The object created by Formula can be saved, for example, in a database field or in a blob document.

Example 1​

A simple formula:

 var $f : 4D.Function
 $f:=Formula(1+2)

 var $o : Object
 $o:=New object("f";$f)

 $result:=$o.f() // returns 3

Example 2​

A formula using local variables:



 $value:=10
 $o:=New object("f";Formula($value))
 $value:=20

 $result:=$o.f() // returns 10

Example 3​

A simple formula using parameters:

 $o:=New object("f";Formula($1+$2))
 $result:=$o.f(10;20) //returns 30

Example 4​

A formula using a project method with parameters:

 $o:=New object("f";Formula(myMethod))
 $result:=$o.f("param1";"param2") // equivalent to $result:=myMethod("param1";"param2")

Example 5​

Using This:

 $o:=New object("fullName";Formula(This.firstName+" "+This.lastName))
 $o.firstName:="John"
 $o.lastName:="Smith"
 $result:=$o.fullName() //returns "John Smith"

Example 6​

Calling a formula using object notation:

 var $feta; $robot : Object
 var $calc : 4D.Function
 $robot:=New object("name";"Robot";"price";543;"quantity";2)
 $feta:=New object("name";"Feta";"price";12.5;"quantity";5)

 $calc:=Formula(This.total:=This.price*This.quantity)

  //sets the formula to object properties
 $feta.calc:=$calc
 $robot.calc:=$calc

  //call the formula
 $feta.calc() // $feta={name:Feta,price:12.5,quantity:5,total:62.5,calc:"[object Formula]"}
 $robot.calc() // $robot={name:Robot,price:543,quantity:2,total:1086,calc:"[object Formula]"}

See also​

4D Blog - Formula: More power behind simplicity
4D Blog - Formula: Think outside the box
4D Blog - Write your own methods for objects
Formula from string

Properties​

Command number1597
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