1. A method for execution by a processor in a computer system, the method comprising: identifying a first class of a plurality of classes, wherein an instance of the first class comprises a first plurality of data fields; identifying a second class of the plurality of classes, wherein an instance of the second class comprises a second plurality of data fields, and wherein the first plurality of data fields includes a data field that references the second class; in response to determining that the first class is immutable and the second class is immutable, constructing a first synthetic immutable class, an instance of which comprises a combination of the first plurality of data fields and the second plurality of data fields; and creating an instance of the first synthetic immutable class in which the first plurality of data fields and the second plurality of data fields occupy a contiguous region of memory.