[swift-evolution] access control

[Félix Cloutier]

I don't understand your conception of encapsulation. The way you're putting it, because of Swift's access modifiers, encapsulation is relative to whether you have access to the original source or not. However, this is trivially true in any condition and whether Swift promoted a "private" or "local" access modifier would change nothing to it.

In my opinion, this solution will be confusing to a lot of people, and the problem that it solves is many orders of magnitude less important than strong typing. A "local" access modifier is not a breakthrough solution that will make it substantially easier to statically reason about programs to make them faster, provide refactoring tools, or help editing. It's a design tool intended for humans only, and it's extremely ambiguous with private.

A new programmer makes a class and asks you if fields and methods should be private or local. What do you tell him?

Félix

> Le 25 janv. 2016 à 14:33:18, Ilya Belenkiy <ilya.belenkiy at gmail.com> a écrit :
> 
>> There would be no difference at all between local and private if you had one class per file.
> 
> AND if this rule was enforced by the compiler. This would also have to be one extension per file, even if it’s one line of code.
> 
> Since this rule is not enforced, at most, this is coding by convention. By the same reasoning, we could have just one type, object, and name every variable by including the type name we want it to be. No need for a strong type system. And anyone insisting that we need a type system would surely be wrong because there would be a very simple solution — just make the type name part of the variable name. And yet, Swift does have a strong type system. It should have strong access control for the very same reason: the compiler can enforce it and eliminate lots of human errors.
> 
>> It seems very very bold to me to say that Swift "doesn't support encapsulation" but that local would solve that problem.
> 
> And yet both statements are true: it is possible to break the class invariant right now without modifying the class source code, and “local” would solve that problem.
> 
>> On Jan 25, 2016, at 1:43 PM, Félix Cloutier <felixcca at yahoo.ca <mailto:felixcca at yahoo.ca>> wrote:
>> 
>> There would be no difference at all between local and private if you had one class per file. It seems very very bold to me to say that Swift "doesn't support encapsulation" but that local would solve that problem.
>> 
>> Félix
>> 
>>> Le 25 janv. 2016 à 13:16:45, Ilya Belenkiy via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>>> 
>>>> A language does not need to have strict access controls in order to be considered OO. 
>>> 
>>> This is a matter of terminology. It still doesn’t change the fact that data encapsulation is a fundamental feature of object oriented programming that is currently not supported.
>>> 
>>>> You don’t even need “classes” to do OO either.
>>> 
>>> In this terminology C is also object oriented. You can have opaque pointers to structs with functions around them. Swift current support for data encapsulation is exactly like that. But people don’t do this kind of programming in C precisely because the compiler can provide a lot more help than this.
>>> 
>>>> This really seems like an academic problem vs a pragmatic problem. 
>>> 
>>> 
>>> It’s very pragmatic. With properly marked access level and well designed interfaces, the class implementor may rely on the compiler to ensure that the class invariants / internal state will not become corrupt. Without it, the code is much more likely to break due to human error. It’s the same reasoning as with having ARC rather than doing manual retain / release and having destructors that are called automatically instead of calling cleanup code manually.
>>> 
>>>> There’s also no concept of “friend” in Swift either
>>> 
>>> file based access level is a good solution for this. But it’s not a solution at all for real data encapsulation.
>>> 
>>>> On Jan 25, 2016, at 12:09 PM, David Owens II <david at owensd.io <mailto:david at owensd.io>> wrote:
>>>> 
>>>> 
>>>>> On Jan 25, 2016, at 4:47 AM, Ilya Belenkiy via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>>> Data encapsulation is indeed one of the cornerstone of OO, but every design decision is a trade-off. Is Python not object-oriented because they lack a private keyword, and have the convention of marking internal items with a leading underscore?
>>>>> 
>>>>> 
>>>>> Then Python has the same problem. A language that *supports* OOP should not leave such an important part of OOP to coding by convention. 
>>>> 
>>>> I think this where you are being lead astray. A language does not need to have strict access controls in order to be considered OO. Languages like C#, Java, and to some extent, C++ tend to make people think this. You don’t even need “classes” to do OO either.
>>>> 
>>>>>> The best anyone can do is make the breaking of encapsulation an explicit choice. I’m intuiting that you think that writing code into the file where the class was defined is not explicit enough.
>>>>> 
>>>>> Right now, it’s impossible to make the distinction: is something truly private or can be used safely in the same file? The language has no way of expressing it. The class internal state is not encapsulated outside the bounds of the class.
>>>> 
>>>> This really seems like an academic problem vs a pragmatic problem. There’s also no concept of “friend” in Swift either, which is another construct that would have be invented to allow the “private” things to be used by others elsewhere. 
>>>> 
>>>> -David
>>> 
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>> 
> 

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