A notion of a monotone object is introduced. A functional language extended by monotone objects preserves relevant properties that effective metacomputation (supercornpilation and specialization) is based upon. The properties are equifinulity (Church-Rosser property), recomputability and their conjunction idem potency. They are necessary and sufficient for memoizirzg. An object-based language meeting idempotency is called object-functional. A technique of dynamic specialization in object-functional languages is presented.