IDL_Object::_overloadFunction

The IDL_Object::_overloadFunction function method allows you to create "function pointers" in IDL. By implementing the _overloadFunction method on your class, users can then make a function call on an object reference. This function call could then execute different code based upon the object's current state.

Note: This method is designed to replicate the default behavior of objects that do not use operator overloading. As a result, object classes that do inherit from the IDL_Object class but that do not override this particular method will throw an error when you try to call the object as a function.

Example

Create an IDL_SMOOTH class that wraps various smoothing functions. Save the following code in a file called idl_smooth__define.pro:

function IDL_Smooth::Init, BOXCAR=boxcar, LEE=lee, MEDIAN=median

  if (KEYWORD_SET(boxcar)) then self.method = 0

  if (KEYWORD_SET(lee)) then self.method = 1

  if (KEYWORD_SET(median)) then self.method = 2

  return, 1

end

function IDL_Smooth::_overloadFunction, data, width, _EXTRA=extra

  case self.method of

    0: result = SMOOTH(data, width, _EXTRA=extra)

    1: result = LEEFILT(data, width, _EXTRA=extra)

    2: result = MEDIAN(data, width, _EXTRA=extra)

  endcase

  return, result

end

pro IDL_Smooth__define

  void = {IDL_Smooth, inherits IDL_Object, method: 0}

end

Now execute the following code to create an IDL_Smooth object and call it like a function:

COMPILE_OPT idl2

FUNC = IDL_Smooth(/MEDIAN)

x = RANDOMU(seed,100)

result = FUNC(x, 9, /DOUBLE)

HELP, result

IDL prints:

RESULT          DOUBLE    = Array[100]

Note: We need to ensure that compile_opt idl2 is set so that parentheses are treated like a function call instead of array indexing.

Syntax

In most cases, this method is called indirectly when you make a function call on your object reference. When called explicitly, the syntax is:

Result = Obj->[IDL_Object::]_overloadFunction( Arg1, Arg2, ..., Keyword1=..., Keyword2=... )

Return Value

The return value is an IDL variable containing whatever result your method decides to return.

Arguments

Arg1...ArgN

The input arguments to your function.

Keywords

The keyword values for your function.

Routine Signature

To overload this function method for an object class, implement a method with the following signature:

FUNCTION class::_overloadFunction, arg1, arg2, ..., Keyword1=...

Version History

8.5	Introduced