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Using IDL: Getting Information About Files and Data |
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Three IDL routines allow you to obtain information about an existing object: OBJ_CLASS, OBJ_ISA, and OBJ_VALID.
Use the OBJ_CLASS function to obtain the class name of a specified object, or to obtain the names of a specified object's direct superclasses. For example, if we create the following class structures:
struct = {class1, data1:0.0 }
struct = {class2, data2a:0, data2b:0L, INHERITS class1 }
We can now create an object and use OBJ_CLASS to determine its class and superclass membership.
; Create an object.
A = OBJ_NEW('class2')
; Print A's class membership.
PRINT, OBJ_CLASS(A)
IDL prints:
CLASS2
Or you can print as superclasses:
; Print A's superclasses. PRINT, OBJ_CLASS(A, /SUPERCLASS)
IDL prints:
CLASS1
See OBJ_CLASS for further details.
Use the OBJ_ISA function to determine whether a specified object is an instance or subclass of a specified object. For example, if we have defined the object A as above:
IF OBJ_ISA(A, 'class2') THEN $ PRINT, 'A is an instance of class2.'
IDL prints:
A is an instance of class2.
See OBJ_ISA for further details.
Use the OBJ_VALID function to verify that one or more object references refer to valid and currently existing object heap variables. If supplied with a single object reference as its argument, OBJ_VALID returns TRUE (1) if the reference refers to a valid object heap variable, or FALSE (0) otherwise. If supplied with an array of object references, OBJ_VALID returns an array of TRUE and FALSE values corresponding to the input array. For example:
; Create a class structure.
struct = {cname, data:0.0}
; Create a new object.
A = OBJ_NEW('CNAME')
IF OBJ_VALID(A) PRINT, "A refers to a valid object." $
ELSE PRINT, "A does not refer to a valid object."
IDL prints:
A refers to a valid object.
If we destroy the object:
; Destroy the object. OBJ_DESTROY, A IF OBJ_VALID(A) PRINT, "A refers to a valid object." $ ELSE PRINT, "A does not refer to a valid object."
IDL prints:
A does not refer to a valid object.
See OBJ_VALID for further details.
IDL Online Help (March 06, 2007)