Memory reference

An access to a location in computer memory, such as an instruction fetch, a read or a write. A page-level reference sequence records the corresponding memory page for each access, retaining repetitions and order.

A null reference denotes the absence of an ordinary referenced software object. In null-terminated linked lists it marks the end of a chain. A search can return it to signal absence, but the caller must check before selecting data members. Short-circuit evaluation can make a combined nonnull-and-property guard safe.

Two program references designate the same mutable object or overlapping mutable state. Binary-update contracts must account for this possibility: an update intended to combine two old values should snapshot both operands before modifying the receiver. A frame condition preserving a distinct operand cannot literally preserve a second reference that aliases the modified receiver.

A copy that duplicates the relevant reachable mutable structure instead of sharing all original references. A Memento pattern snapshot containing mutable arrays must preserve their saved contents against subsequent mutation, whether by a suitable deep copy or by an immutable persistent representation. The intended ownership graph and any permitted sharing must be specified; blindly copying one outer object is only a shallow copy.

The identity of a particular allocated object, distinct from equality of its current fields. Two different linked list nodes can store identical payloads, while two references can designate the same node. Pointer algorithms must state whether they preserve identities, copy payloads or allocate replacements. Testing cycle completion by identity avoids confusing two equal-looking nodes.

An ordered sequence of memory references, recording repetitions as well as addresses. The example under memory cache records twelve reads in decimal physical addresses; the trace itself does not determine cache hits until cache line size, capacity, initial contents, placement and replacement are specified.