1178 GENERICITY VERSUS INHERITANCE SB.4 class INTEGER COMPARABLE inherit COMPARABLE creation put feature--Initialization put(v:INTEGER)is - Initialize from v. do item:=new end feature--Access item:INTEGER: --Value associated with current object feature--Basic operations infix "<="(other:like Current):BOOLEAN is --Is current object less than or equal to other? do Result:=(item <other.item)end, end--class INTEGER COMPARABLE To find the minimum of two integers,you may now apply function minimum to entities icl and ic2,whose type is not INTEGER but INTEGER COMPARABLE: ic3 :icI.minimum (ic2) To use the generic infix "<=and minimum functions,you must renounce direct references to integers,using INTEGER COMPARABLE entities instead;hence the need for attribute item and routine put to access and modify the associated integer values.You will introduce a similar heirs of COMPARABLE,such as STRING COMPARABLE,and REAL COMPARABLE,for each type requiring a version of minimum. Note that the mechanism of anchored declaration is essential to ensure type correctness.If the argument to minimum in COMPARABLE had been declared as a COMPARABLE,rather than like Current,then the following call would be valid: icl.ninimum(c） even if c is a COMPARABLE but not an INTEGER COMPARABLE.Clearly,such a call should be disallowed.This also applies to the previous example,RING ELEMENT. Having to declare features item and put for all descendants of COMPARABLE,and hence sacrificing the direct use of simple types,is unpleasant.There is also a performance cost:rather than manipulating integers or strings we must create and use wrapper objects of types such as INTEGER COMPARABLE.But by paying this fixed price in both ease of use and efficiency we do achieve the full emulation of constrained genericity by inheritance.(In the final notation,of course,there will be no price at all to pay.) Emulating constrained genericity (1) It is possible to emulate constrained genericity through inheritance,by using wrapper classes and the corresponding wrapper objects.1178 GENERICITY VERSUS INHERITANCE §B.4 class INTEGER_COMPARABLE inherit COMPARABLE creation put feature -- Initialization put (v: INTEGER) is -- Initialize from v. do item := new end feature -- Access item: INTEGER; -- Value associated with current object feature -- Basic operations infix "<=" (other: like Current): BOOLEAN is -- Is current object less than or equal to other? do Result := (item <= other ● item) end; end -- class INTEGER_COMPARABLE To find the minimum of two integers, you may now apply function minimum to entities ic1 and ic2, whose type is not INTEGER but INTEGER_COMPARABLE: ic3 := ic1 ● minimum (ic2) To use the generic infix "<=" and minimum functions, you must renounce direct references to integers, using INTEGER_COMPARABLE entities instead; hence the need for attribute item and routine put to access and modify the associated integer values. You will introduce a similar heirs of COMPARABLE, such as STRING_COMPARABLE, and REAL_COMPARABLE, for each type requiring a version of minimum. Note that the mechanism of anchored declaration is essential to ensure type correctness. If the argument to minimum in COMPARABLE had been declared as a COMPARABLE, rather than like Current, then the following call would be valid: ic1 ● minimum (c) even if c is a COMPARABLE but not an INTEGER_COMPARABLE. Clearly, such a call should be disallowed. This also applies to the previous example, RING_ELEMENT. Having to declare features item and put for all descendants of COMPARABLE, and hence sacrificing the direct use of simple types, is unpleasant. There is also a performance cost: rather than manipulating integers or strings we must create and use wrapper objects of types such as INTEGER_COMPARABLE. But by paying this fixed price in both ease of use and efficiency we do achieve the full emulation of constrained genericity by inheritance. (In the final notation, of course, there will be no price at all to pay.) Emulating constrained genericity (1) It is possible to emulate constrained genericity through inheritance, by using wrapper classes and the corresponding wrapper objects