OOP vs. Functional Programming (2014)

Re:OOP vs. Functional Programming (2014) by lmm on Tuesday October 30, 2018 @05:10AM (#18334920)

> When you reason about something as a group, that reasoning operates with the details hidden. When you apply that abstract reasoning to a concrete problem, of course that information is still there. Abstraction is a boundary that looks different on either side. In a similar vein of your example, the compiler knows all the information you're hiding through your program abstractions, but from the point of view of pieces of your code, that abstraction has hidden something.

If I write a function like:

    f(x) = x + 2

would you say the value of x is "hidden" in the expression x + 2? I would say no: it's clear that there is a value of x at the point where we evaluate that expression. That's a different kind of thing from the OO style where we write o.f() and genuinely can't distinguish whether there is relevant internal state in o (and whether that state is mutated by the call to f()), or not.

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Re:OOP vs. Functional Programming (2014) by danharaj on Tuesday October 30, 2018 @04:04PM (#18340811)

There is a difference between a function `f` and the expression `x + 2` in your example. In fact, `f` as a function completely hides the expression from which it was defined. Usually functions are considered equal if they have the same values at every point. The upshot is, you can define a function from two different expressions and they can end up being the "same" function. This is indeed the hiding of some information.

In the composition of functions, f . g (x) = f(g(x)), that there is a result of g(x) is hidden by the composition, which only allows examination of the first input and the final output.

There is nothing special about OOP here.

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Re:OOP vs. Functional Programming (2014) by lmm on Wednesday October 31, 2018 @01:40PM (#18347733)

> There is a difference between a function `f` and the expression `x + 2` in your example. In fact, `f` as a function completely hides the expression from which it was defined. Usually functions are considered equal if they have the same values at every point. The upshot is, you can define a function from two different expressions and they can end up being the "same" function. This is indeed the hiding of some information.

It's hiding the differing constructions, but at that point I don't see that as a true difference. (\x . x + 2) . (\x . x + 2) seems to me to be the same value as \x . x + 4 in exactly the same way that 2 + 2 is the same value as 4.

> In the composition of functions, f . g (x) = f(g(x)), that there is a result of g(x) is hidden by the composition, which only allows examination of the first input and the final output.

> There is nothing special about OOP here.

Having mutable state hidden/encapsulated with a bundle of functions that may be entangled with that state is unique to OOP; as I said in the side thread, hidden structure is not the same as hidden state.

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