Syntax

  record-type-name cast record-expression

You can use cast to force a record of an extended type that is resident on a shelf of its base type to be treated as its own type rather than the base type.

One example of when this is useful is when you call a dynamically overloaded function and then want to access fields in the record returned by that function. You know what type the result is, based on the type you passed to it, but OmniMark still treats it as a record of the base type. Here is an example:

  declare record point
   field integer x
   field integer y

  declare record pixel
   extends point
   field stream color

  define dynamic point function move-point
   value point a
   to value point b
   as
     local point c
     set c:x to b:x
     set c:y to b:y
     return c

  define overriding point function move-point
   value pixel a
   to value point b
   as
     local pixel c
     set c:x to b:x
     set c:y to b:y
     return c

  process
   local point a variable
   local pixel b
   local point c

   set b:x to 5
   set b:y to 78
   set b:color to "red"

   set c:x to 87
   set c:y to 56

   output (pixel cast move-point b to c):color

Related Syntax    declare record    define overloaded function, dynamic, overridding    do select-type

Related Concepts    Records, extended

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