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Validating Input

The pointer returned by astReadastRead (§15.4) could identify any class of ObjectObject—this is determined entirely by the external data being read. If it is necessary to test for a particular class (say a FrameFrame), this may be done as follows using the appropriate member of the astIsA1#1Class2#2astIsA1#1Class2#2 family of functions:

232#232

Note, however, that this will accept any Frame, so would be equally happy with a basic Frame or a SkyFrameSkyFrame. An alternative validation strategy would be to obtain the value of the Object's ClassClass attribute and then test this character string, as follows:

233#233

This would only accept a basic Frame and would reject a SkyFrame.