OB Is defined

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4D v20 R7

OB Is defined


OB Is defined ( object {; property} ) -> Function result

Parameter	Type	Description
object	Object, Object Field	Structured object
property	Text	If passed = property to check, if omitted = check object
Function result	Boolean	If property omitted: True if object is defined, otherwise False. If property passed: True if property is defined, otherwise False

Description

The OB Is defined command returns True if object or property is defined, and False otherwise.

object must have been created using the _O_C_OBJECT command or designate a 4D object field.

By default, if you omit the property parameter, the command checks whether the object is defined. An object is defined if its contents has been initialized.

Note: An object can be defined but empty. To find out if an object is undefined or empty, use the OB Is empty command.

If you pass the property parameter, the command checks whether this property exists in object. Note that the property parameter is case sensitive.

Example 1

Syntax testing the initialization of an object:

 C_OBJECT($object)

 $def:=OB Is defined($object) // $def=false since $object is not initialized

 

 OB SET($object;"Name";"Martin")

 OB REMOVE($object;"Name")

 $def2:=OB Is defined($object) // $def2=true since $object is empty {} but has been initialized

Example 2

Test for existence of a property:

 C_OBJECT($ref)

 OB SET($ref;"name";"smith";"age";42)

  //...

 If(OB Is defined($ref;"age"))

  //...

 End if

This test is equivalent to:

If(OB Get type($Object;"name")#Is undefined)