Popular conceit about learning programming languages

[Dennis Lee Bieber]

Brad Hards fed this fish to the penguins on Thursday 21 November 2002 
02:55 pm:

> 
> The big thing I don't yet really get is OO. I don't see solutions in
> terms of classes yet. In the natural language analogy, this is the
> equivalent of never come across a tonal language (for those not
> familiar, this is very roughly where the meaning (in a denotational
> sense, not just a connotational sense) of a sound varies with how it
> is pronounced - the same sound with a rising frequency might be a
> verb, while a flat frequency might be a noun). No OO is a big hole,
> and while I can program using classes (in C++ and Python) a little
> bit, I don't really "see the solution" in those terms yet.
>
        Unfortunately, OO is not a language specific feature... It is a whole 
philosophy of how to look at a problem.

        While not easily done, one /can/ apply OO to even FORTRAN applications.


        I'll admit I tend to have difficulty applying OO to abstract things 
(like records in a database <G>).

        Much easier to learn by applying to real-world objects. Are you 
familiar with RPN calculators? (mainly because I don't want hassle with 
the ugliness of arithmetic/algebraic/algebraic-with-parens processing).

        The simplest RPN calculator has a 4-entry stack, a display, 10 digit 
buttons, a decimal button, four functions, clear, and an enter button.

        Objects are: button, stack, display.

        Stack object has "methods" "push" and "pop" (with internal data for 
the stack itself)
                push does:
                        shift the stack data
                        save new value
                        display.display(value)
                pop does:
                        str = stack value
                        shift stack data (duplicate top of stack)
                        return str

        Display object has "display" method (do whatever is needed to drive 
display)

        Button object has sub-classes of "digit" (include decimal here for 
simplicity), "operator", "enter", "clear"

        Digit buttons, when pressed perform essentially the following:
                str = stack.pop
                append <button constant digit> to str
                stack.push(str)

        Operator buttons perform:
                str1 = stack.pop
                str2 = stack.pop
                rslt = value(str2) <operator constant> value(str1)
                stack.push(rslt)


        And similar for enter and clear. NOTE: I've not covered the fact that 
a flag is needed in the stack to indicate that the entry is complete 
(which means digit buttons start a new entry, rather than append to 
current entry).


        Or a radio... The basic radio has a tuner and an amplifier. A tuner 
has frequency as a settable parameter, amplifier has volume setting. 
Fancier radios may extend the object with balance, FM/AM, frequency 
band settings, etc.

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