B.J. MacLennan. Values and objects in programming languages. Sigplan Notices, 17(12):70--79, December 1982.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....specification language VSL and the object specification language OSL. These are described in chapters 2 and 3. In this section we describe intuitively what the difference between values and objects is. A good informal description of the distinction between values and objects is given by MacLennan [14]. The following account is based upon this and on an analysis given in Wieringa [22] To determine thoughts, take the natural numbers as typical examples of values, and the set of all possible cars as typical examples of objects. First of all, values and objects both are discrete entities, by ....

B.J. MacLennan. Values and objects in programming languages. Sigplan Notices, 17(12):70--79, December 1982.

.... of practical object oriented languages is the ability to update complex object structures (e.g. those with shared subcomponents and circular structures) Furthermore, the identity of an object is often very important, and must be maintained even when the data values of the object change [KC86] Mac82] For these reasons, most object oriented languages use reference semantics, which means that variables contain references (or pointers) to objects rather than containing the actual object value. This allows two variables to contain the same reference and thus refer to the same object. In such ....

B. J. MacLennan. Values and objects in programming languages. SIGPLAN Notices, 17(2), December 1982. Ref. on page 128.

....possible actions. We should stress that, in our approach, values such as the booleans or the natural numbers are not objects. Contrarily to objects, values do not have a state, they cannot be changed, created or destroyed. We can only apply functions to values in order to obtain other values. See [43] for an interesting discussion on the differences between values and objects in Computing. The way the actions update the attributes is specified through axioms of the form ############################# The (modal) operators ######## are as in dynamic logic [34] see also [39] for the use of ....

MacLennan 82, "Values and Objects in Programming Languages", SIGPLAN Notices 17(12), 1982, 70-79

....value of their attributes might well suffice. Secondly, object identity emphasizes the durable nature of objects, because identity persists notwithstanding changes to the state. The temporal nature of objects and the reliance of this feature upon the concept of object identity is well documented [Mac82] A software engineer seeking to develop an object oriented specification has several options, namely: 1. a model can be developed which includes no notion of object identity (the extent to which such a model is object oriented is controversial) 2. a model can be developed which relies upon ....

B MacLennan. Values and Objects in Programming Languages. SIGPLAN Notices, 17(12):9--14, 1982.

....inefficient and annoying. If DSTRING were not a limited type, we could have utilized the following code: declare fx: constant dstring : f(x) begin return h(fx,g(fx) end; However, due to Ada83 s confusion over the difference between a variable a container for a value and a value itself [MacLennan82] [Baker93ER] Ada83 mistakenly thinks that the : in a constant initialization is a form of assignment, when it is just another form of renaming, only for values rather than for variables. We are therefore forced to use the following subterfuge, which works in Ada83 even for limited types: ....

MacLennan, B.J. "Values and Objects in Programming Languages". Sigplan Not. 17,12 (Dec. 1982), 70-79.

....of references. Of course, we can achieve automatic initialization of MutableObject by directly declaring it to be a value, resulting in a much simpler structure and no delegation overhead. Yet, this is possible only if value semantics (e.g. no sharing, no efficient updates) is intended [18, 10]. ffl Implicit creation. Smalltalk allows to change the type of an object without affecting its identity. Ergo, a void value may change to an object and vice versa. If a void value can not deal with a message it may delegate it to its associated object and then become: 4 the object itself. ....

B. J. MacLennan. Values and objects in programming languages. SIGPLAN Notices, 17(12):70--79, December 1982.

....languages associate a variable with a value. If we are to consider realistic procedural or object oriented languages we must make the distinction between variables, objects and values. The concept of object is needed to reason about sharing, as it is meaningless to talk about the sharing of values [25]. This is true even in the case of primitive types like integer: integer variables denote objects that contain (representations of) values. We use this model to accurately describe the behaviour of a program when aliasing is present. In the case of integers, aliasing can be created when using ....

B. J. MacLennan. Values and objects in programming languages. SIGPLAN Notices, 17(12):70--79, December 1982.

....OF CONTROLLED TYPES In order to understand how user defined initialization, finalization, and assignment is managed, it is necessary to grasp that controlled types provide hooks to the birth and death of objects and values. The distinction between objects and values is important for programming [Mac82]. In Ada, the term object subsumes variables, constants, and heap allocated storage. For instance, a variable is born where its scope starts and dies where its scope ends. A heap objects is born when storage is allocated and dies when either it becomes inaccessible or the storage is deallocated. ....

B.J. MacLennan. Values and Objects in Programming Languages. SIGPLAN Notices, Vol. 17, No 12, Dec. 1982, pp. 70-79.

....OF CONTROLLED TYPES In order to understand how user defined initialization, finalization, and assignment is managed, it is necessary to grasp that controlled types provide hooks to the birth and death of objects and values. The distinction between objects and values is important for programming [Mac82]. In Ada, the term object subsumes variables, constants, and heap allocated storage. For instance, a variable is born where its scope starts and dies where its scope ends. A heap objects is born when storage is allocated and dies when either it becomes inaccessible or the storage is deallocated. ....

B.J. MacLennan. Values and Objects in Programming Languages. SIGPLAN Notices, Vol. 17, No 12, Dec. 1982, pp. 70-79.

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MacLennan, B.J. "Values and Objects in Programming Languages". Sigplan Not. 17,12 (Dec. 1982),70-79.

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MacLennan, B.J. "Values and Objects in Programming Languages". Sigplan Not. 17,2 (Dec. 1982),70-79.

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