STRING_CAST

---

General Form:

---

The STRING_CAST expression is used to declare a string expression that has a type based on a record to be a string based on a record derived from the base record. It is an error to cast a string not being declared to be of a record type. No run-time checks are performed making the operation quick, but open to misuse by the programmer.

DEFRECORD BaseRec
    FLD TypeName$64
END RECORD
DEFRECORD DerivedRec EXTENDS RECORD BaseRec
    FLD x
END RECORD
DIM a$_DerivedRec
FLD(a$.TypeName$)="DerivedRec"
// Can pass this BYREF to a function expecting the BaseRec
'BaseFn(BYREF a$)
DEFSUB 'BaseFn(BYREF p$_BaseRec)
    // Determine from p$ that it must have been declared as a DerivedRec
    IF (FLD(p$.TypeName$) == "DerivedRec")
         FLD(STRING_CAST(_DerivedRec, p$).x) = 10
         'DerivedFn(BYREF STRING_CAST(_DerivedRec, p$))
    END IF
END SUB

GenericRecordType

It is an error to cast a string not being declared to be of a record type. If a parameter is known to contain a string of some record type it is possible to define the parameter to be of type _GenericRecordType and then use STRING_CAST when the correct type has been determined. This is demonstrated in the following example:

DEFSUB 'GenericFn(BYREF p$_GenericRecordType, typeparam)
    SELECT CASE typeparam
    CASE type1
         'some_type1_fn(BYREF STRING_CAST(_type1, p$))
    CASE type2
         'some_type2_fn(BYREF STRING_CAST(_type2, p$))
    END SELECT	 
END SUB