To specify that an argument should be passed by reference rather than by value, use the keyword reference immediately after the argument type in the declaration for the external function. Note that you can  also specify the keyword as ref. The keyword reference is not necessary when declaring a function that uses a structure because structures can be passed only by reference. To specify that the type of a reference argument may vary between calls to the function, specify only the keyword reference without a data type. This indicates that the type of the argument passed to the C function will be void * (an anonymous reference), as shown below.

function FuncVoid(reference: Param1)

returns integer library "DLLNAME"

Caution:        Exercise care in using anonymous references.

For further information about this extension to the DLL call interface, refer to Using the Extended Call Interface.