Function

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.

Inheritance

4D handles several kinds of Function objects, inheriting from the 4D.Function class:

• 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 formula code stored in 4D.Formula objects,
• method functions, i.e. functions that can execute source code as text stored in 4D.Method objects.

Executing code in Function objects

Function objects can be encapsulated in object properties:

var $message : 4D.Formula
$message:=Formula(ALERT("Hello world"))
$f:={message: $message}

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 function object in $o

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

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

Summary

.apply() : any .apply( thisObj : Object { ; params : Collection } ) : any executes the function object to which it is applied, passing parameters as a collection, and returns the resulting value
.call() : any .call( thisObj : Object { ; ...params : any } ) : any executes the function object to which it is applied, with one or more parameter(s) passed directly, and returns the resulting value
.source : Text contains the source code of the function as text

.apply()

History

Release	Changes
21 R3	Support of 4D.Methods objects
17 R3	Added

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

Parameter	Type		Description
thisObj	Object	->	Object to be returned by the This command in the function
params	Collection	->	Collection of values to be passed as parameters to the function
Result	any	<-	Value from function execution

Description

The .apply() function executes the function object to which it is applied, passing parameters as a collection, and returns the resulting value.

In the thisObj parameter, you can pass a reference to the object to be used as This within the function. Pass Null if you do not want to use This but you want to send parameters.

You can pass a collection to be used as parameters in the function using the optional params parameter:

• in 4D.Formula objects, parameters are passed in $1...$n in the formula.
• in other 4D.Function objects such as 4D.Method objects, parameters are passed in declared method parameters.

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

.call()

History

Release	Changes
21 R3	Support of 4D.Methods objects
17 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 function
params	any	->	Values to be passed as parameters to the function
Result	any	<-	Value from function execution

Description

The .call() function executes the function object to which it is applied, with one or more parameter(s) passed directly, and returns the resulting value.

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

You can pass values to be used as parameters in the function using the optional params parameter:

• in 4D.Formula objects, parameters are passed in $1...$n in the formula.
• in 4D.Method objects, parameters are passed in declared method parameters.

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

Release	Changes
21 R3	Support of 4D.Methods objects
18 R2	Added

.source : Text

Description

The .source property contains the source code of the function as text.

The returned value is the original text used to create the 4D.Formula or 4D.Method object but reformatted.

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)"