Re: "Polymorphism and Overloading in C++"

From:
ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups:
comp.lang.c++
Date:
3 Nov 2014 23:27:34 GMT
Message-ID:
<polymorphism-20141104001800@ram.dialup.fu-berlin.de>
Christopher Pisz <nospam@notanaddress.com> writes:

The way I see it, overloading is one facet of polymorphism, while
inheritance is the other. Depends which interviewer you talk to, some
have one in mind or the other or both. Best to go into both usually.


  The term ?polymorphism? was coined by Strachey in 1967. At
  least this is the common wisdom, even though, AFAIK, Strachey
  did not give proper definition at all, but just talked about
  polymorphism. But maybe I just have not found his definition yet.

  As far as I have access to Strachey's words, I cannot see
  any reason why overloaded operators should not be called
  ?polymorphic?. On the opposite, Strachey said:

      ?In ad hoc polymorphism there is? ... ?All the ordinary
      arithmetic operations and functions come into this category.?!

  Of course, he did not refer to C++ (in 1967), but possibly
  to some programming language.

  My personal definition of polymorphism is: I call a
  function symbol ?f? polymorphic, when the meaning of
  ?f(x)? is mapped to one of ?f1(x)?, ?f2(x)?, ... by
  the type of x. This definition encompasses operator
  overloading. In C++, operator overloading is compile-
  time polymorphism, not run-time polymorphism, though.

  (By my definition ?polymorphism? is an implementation
  detail. Therefore, it is possible that, sometimes, one does
  not know whether a function symbols is polymorphic. For
  example, I might know that ?-? can be applied to both int
  and double. When the processor used has a single CHS opcode
  for both int and double values, there is only one
  implementation, so it is not polymorphic. ?-? always means
  ?CHS?. Another processor used might have a ?CHSI? for int
  and a ?CHSD? for double, and C++ maps ?-? to ?CHSI? or
  ?CHSD? depending of the type of the operand for this other
  processor, so in this case ?-? is polymorphic. But for the
  C++ programmer it suffices to know that he can apply it to
  both int and double with the intended semantics.)

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