Re: [boost] [optional] Safe optional

On Mon, 17 Nov 2014 19:57:08 -0800, Vladimir Batov wrote:

On 11/18/2014 11:25 AM, Mostafa wrote:

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On Mon, 17 Nov 2014 13:12:56 -0800, Vladimir Batov wrote:

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On 11/17/2014 09:12 PM, Mostafa wrote:

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On Sun, 16 Nov 2014 23:04:43 -0800, Andrzej Krzemienski wrote:

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Hi Everyone, I would like to run an idea through everyone in this list. There is a recurring complaint about Boost.Optional that it allows you to do "unsafe" things: 1. Inadvertent mixed comparisons between T and optional<T> 2. Unintended conversion from T to optional<T>

... And after using "optional" quite a bit I can say I personally won't be very happy. IMO "optional" has been born as a practical solution to a real problem and IMO it solves it quite well. Yes, it has certain behavior that the user needs to be aware of... but what class does not impose restrictions of that kind?

Not all classes have gotchas. And, IMO, C++ has too many gotchas as it is.

Well, that's far too broad a statement to be argued over... still, my logic behind restrictions-related statement is that, say, a class provides a service, nothing is free, so to make use of the service the user needs to give something back... be that adhering to certain deployment pattern or API or something.

I'm in agreement with the last sentence. What I'm saying is that the current optional usage pattern, IMHO, is just too inconsistent.

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Any potential functional/behavioral change has to be looked at individually.

For example, I do agree that that there should not be implicit optional<T> to T conversion. I was not even aware there was such.

However, implicit T to optional<T> conversion has a very practical purpose.

And that leads to the intractable rebinding gotcha for optional.

Yes, I've heard of that "beast". In all honesty to me it looks quite esoteric and beyond the realm of practical every-day programming. I suspect if it's taken out altogether, 95% of the users will not even notice. I can be wrong though and prepared to be convinced otherwise... if you show me a practical example where it's a must-have... Without such I fully understand/support the decision to get rid of optional for std::tr2::optional proposal. So, re-phrasing J. Stalin's "no man, no problem" -- "no "feature", no problem.

And that exacerbates the problem doesn't it? If optional is just used 5% of the time, then when that particular gotcha is hit, it'll be that much harder to diagnose the issue. Not all programmers are full time C++ programmers, not all programmers develop new code full time, some do quite a bit of maintenance, so not everyone is going to be an expert in the ins and outs of any particular library. The simpler a library is to use, the simpler it will be to maintain the code which uses it.

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For example,

int value(optional<int> =optional<int>());

allows me to shrink the API as value getter and setter are merged into one function. Namely,

int k = value(); // Get the value value(22); // Set the value. Implicit conversion of T to optional<T> Instead, asking the user to call explicitly

value(optional<22>)

is a professional suicide.

Templates are neither new nor unknown in C++. If you find yourself typing too much, just use a typedef.

Hmm, not sure I follow what templates have to do with it... and the amount of typing is irrelevant. The point was if conceptually user expects to use/deal with "int", then the requirement to explicitly specify optional<int> looks unreasonably heavy and unnatural.

Then why specify in the interface in the first place?

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2. As for the separate/additional "safe" optional, I am personally not that thrilled by the idea as of now. IMO that'll result in user-base fragmentation, incompatibilities and inevitably more confusion in the end.

If there are multiple valid yet incompatible design choices, then IMO there is nothing wrong with providing alternatives.

I do not believe it's that simple. If, when referring to "incompatible design choices", we are talking about differences like "car vs. truck", then I'd argue that those are not alternatives as they serve quite distinct purposes and, therefore, adhere to different designs. Otherwise, having "incompatible design choices" like a toothbrush and a "safe" toothbrush and a "whistling" toothbrush are distracting and confusing and IMO counter-productive. I had an impression that "safe" optional suggestion was more in the latter camp as it still very much wanted to be "optional"... but a tiny bit different. It might well be that I misunderstood.

They will be competing libraries. But I don't see that as a bad thing. It will only be confusing if the rationale for their difference is not well documented.