Sent from my iPad
> On Feb 2, 2017, at 7:11 AM, Matthew Johnson <matt...@anandabits.com> wrote:
>
>>>
>>>
>>> Furthermore, we emphatically do *not* need to make the distinction you
>>> claim between “infinite” and “incomplete” ranges, which *is* needless
>>> hairsplitting.
>>
>> Strongly disagree, unless you can describe the semantics of the type WITHOUT
>> giving it different semantics depending on how it is used.
>
> This is the point that convinced me. I’m going to take a closer look at
> Brent’s `RangeExpression` design which I must admit I only skimmed in the
> earlier discussion.
We already have exactly this situation with CountableRange (which will merge
with Range when conditional conformances land). When used as a Collection, it
means "every index value starting with the lowerBound and ending just before
the upperBound". When used for slicing, it means, roughly, "take every one of
the collection's indices that are in bounds." These are not the same thing. A
collection's indices need not include every expressible value of the Index type
between startIndex and endIndex.
The whole point of the name RangeExpression is to acknowledge this truth:
ranges in Swift bits of syntax whose meaning is given partly by how they are
used. In fact, now that I say it, in that respect ranges are not all that
different any other type: the meaning of a Double or an Array<String> or a Bool
is also interpreted by the methods to which it is passed, and can have
completely different results depending on that context.
chillaxing-ly y'rs,
Dave
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