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From: Dean Michael Berris <dberris@google.com>
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Subject: Re: optional<T>, one more value or two states
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On Fri, Jan 25, 2013 at 3:56 PM, Tony V E <tvaneerd@gmail.com> wrote:
> On Thu, Jan 24, 2013 at 7:10 PM, Dean Michael Berris <dberris@google.com> wrote:
>>
>> In my opinion:
>>
>> - There's a precedent in other languages for a ".get(default_value)".
>> Why don't we have this for optional instead?
>>
>
> opt.get(17) doesn't look like it is using a default to me.  Typically
> get(17) is get the 17th element or lookup with key = 17, etc.
>

Right. I was confused by Python's dict that has a method "get" which
takes the key and the default value to return if the key is not found.

>
>> - Why are we forcing pointer semantics on optional? Maybe there's a
>> different concept here at play.
>>
>
> Because much of optional's interface is similar to pointers:  you
> access the value with *opt and opt can be NULL.
>

Right, but that's a good thing right? Something you can copy around,
acts as a value, and gives you pointer semantics. It could be that the
answer is a standalone function that works with pointers, optionals,
and NullableProxy objects like:

template <class T, class NullableProxy>
T get(NullableProxy &&p, T&& t) {
  if (p) return *p;
  return std::forward<T>(t);
}

> That is the essential "problem" with optional.  Sometimes it acts
> value-ish, sometimes pointer-ish.  It is like quantum physics -
> sometimes a particle, sometimes a wave...
>

I thought it was always a value. Is there any confusion in that?

-- 

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