Function

About Function objects

A 4D.Function object contains a piece of code that can be executed from an object, either using the () operator, or using the apply() and call() functions. 4D proposes three kinds of Function objects:

• native functions, i.e. built-in functions from various 4D classes such as collection.sort() or file.copyTo().
• user functions, created in user classes using the Function keyword.
• formula functions, i.e. functions that can execute any 4D formula.

Formula Objects

The Formula and Formula from string commands allow you to create 4D.Function objects to execute any 4D expression or code expressed as text.

Formula objects can be encapsulated in object properties:

 var $f : 4D.Function
 $f:=New object
 $f.message:=Formula(ALERT("Hello world"))

This property is an "object function", i.e. a function which is bound to its parent object. To execute a function stored in an object property, use the () operator after the property name, such as:

 $f.message() //displays "Hello world"

Syntax with brackets is also supported:

 $f["message"]() //displays "Hello world"

Note that, even if it does not have parameters (see below), an object function to be executed must be called with ( ) parenthesis. Calling only the object property will return a new reference to the formula (and will not execute it):

 $o:=$f.message //returns the formula object in $o

You can also execute a function using the apply() and call() functions:

 $f.message.apply() //displays "Hello world"

Passing parameters

You can pass parameters to your formulas using the sequential parameter syntax based upon $1, $2...$n. For example, you can write:

 var $f : Object
 $f:=New object
 $f.message:=Formula(ALERT("Hello "+$1))
 $f.message("John") //displays "Hello John"

Or using the .call() function:

 var $f : Object
 $f:=Formula($1+" "+$2)
 $text:=$f.call(Null;"Hello";"World") //returns "Hello World"
 $text:=$f.call(Null;"Welcome to";String(Year of(Current date))) //returns "Welcome to 2019" (for example)

Parameters to a single method

For more convenience, when the formula is made of a single project method, parameters can be omitted in the formula object initialization. They can just be passed when the formula is called. For example:

 var $f : 4D.Function

 $f:=Formula(myMethod)
  //Writing Formula(myMethod($1;$2)) is not necessary
 $text:=$f.call(Null;"Hello";"World") //returns "Hello World"
 $text:=$f.call() //returns "How are you?"

  //myMethod
 #DECLARE ($param1 : Text; $param2 : Text)->$return : Text
 If(Count parameters=2)
    $return:=$param1+" "+$param2
 Else
    $return:="How are you?"
 End if

Parameters are received within the method, in the order they are specified in the call.

Summary

.apply() : any .apply( thisObj : Object { ; formulaParams : Collection } ) : any    executes the formula object to which it is applied and returns the resulting value
.call() : any .call( thisObj : Object { ; ...params : any } ) : any    executes the formula object to which it is applied and returns the resulting value
.source : Text     contains the source expression of the formula as text

Formula

History

Version	Changes
v17 R6	Renamed (New formula -> Formula)
v17 R3	Added

Formula ( formulaExp : Expression ) : 4D.Function

Parameter	Type		Description
formulaExp	Expression	->	Formula to be returned as object
Result	4D.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:

• .call() or .apply() methods, or
• object notation syntax (see formula object).

 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]"}

Formula from string

History

Version	Changes
v17 R6	Renamed New formula from string -> Formula from string
v17 R3	Added

Formula from string( formulaString : Text ) : 4D.Function

Parameter	Type		Description
formulaString	Text	->	Text formula to be returned as object
Result	4D.Function	<-	Native object encapsulating the formula

Description

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

This command is similar to Formula, except that it handles a text-based formula. In most cases, it is recommended to use the Formula command. Formula from string should only be used when the original formula was expressed as text (e.g., stored externally in a JSON file). In this context, using syntax with tokens is highly advised.

Because local variable contents can not be accessed by name in compiled mode, they can not be used in formulaString. An attempt to access a local variable with Formula from string will result in an error (-10737).

Example

The following code will create a dialog accepting a formula in text format:

 var $textFormula : Text
 var $f : 4D.Function
 $textFormula:=Request("Please type a formula")
 If(ok=1)
    $f:=Formula from string($textFormula)
    ALERT("Result = "+String($f.call()))
 End if

...and execute the formula:

.apply()

History

Version	Changes
v17 R3	Added

.apply() : any
.apply( thisObj : Object { ; formulaParams : Collection } ) : any

Parameter	Type		Description
thisObj	Object	->	Object to be returned by the This command in the formula
formulaParams	Collection	->	Collection of values to be passed as $1...$n when formula is executed
Result	any	<-	Value from formula execution

Description

The .apply() function executes the formula object to which it is applied and returns the resulting value. The formula object can be created using the Formula or Formula from string commands.

In the thisObj parameter, you can pass a reference to the object to be used as This within the formula.

You can also pass a collection to be used as $1...$n parameters in the formula using the optional formulaParams parameter.

Note that .apply() is similar to .call() except that parameters are passed as a collection. This can be useful for passing calculated results.

Example 1

 var $f : 4D.Function
 $f:=Formula($1+$2+$3)

 $c:=New collection(10;20;30)
 $result:=$f.apply(Null;$c) // returns 60

Example 2

 var $calc : 4D.Function
 var $feta; $robot : Object
 $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)

 $calc.apply($feta) // $feta={name:Feta,price:12.5,quantity:5,total:62.5}
 $calc.apply($robot) // $robot={name:Robot,price:543,quantity:2,total:1086}

.call()

History

Version	Changes
v17 R3	Added

.call() : any
.call( thisObj : Object { ; ...params : any } ) : any

Parameter	Type		Description
thisObj	Object	->	Object to be returned by the This command in the formula
params	any	->	Value(s) to be passed as $1...$n when formula is executed
Result	any	<-	Value from formula execution

Description

The .call() function executes the formula object to which it is applied and returns the resulting value. The formula object can be created using the Formula or Formula from string commands.

In the thisObj parameter, you can pass a reference to the object to be used as This within the formula.

You can also pass values to be used as $1...$n parameters in the formula using the optional params parameter(s).

Note that .call() is similar to .apply() except that parameters are passed directly.

Example 1

 var $f : 4D.Function
 $f:=Formula(Uppercase($1))
 $result:=$f.call(Null;"hello") // returns "HELLO"

Example 2

 $o:=New object("value";50)
 $f:=Formula(This.value*2)
 $result:=$f.call($o) // returns 100

.source

History

Version	Changes
v18 R2	Added

.source : Text

Description

The .source property contains the source expression of the formula as text.

This property is read-only.

Example

 var $of : 4D.Function
 var $tf : Text
 $of:=Formula(String(Current time;HH MM AM PM))
 $tf:=$of.source //"String(Current time;HH MM AM PM)"