[swift-evolution] [Pitch] 'Double modulo' operator

[Adam Nemecek]

> I think this is a very particular case

I disagree. Swift has the concept of a range all over the place and this is
a fundamental range operation.

>  As you pointed out this already can be implemented using resources
already available in the language when needed.

Right. A lot of things in the standard library can be implemented using
resources already available, it's about the ergonomics.



On Sat, May 21, 2016 at 1:44 PM, Leonardo Pessoa <me at lmpessoa.com> wrote:

> Adam, I think this is a very particular case and not something that needs
> to be added to the language. As you pointed out this already can be
> implemented using resources already available in the language when needed.
>
>
>
> On 21 May 2016 at 17:22, Adam Nemecek via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Hello,
>>
>> I think that Swift could use the 'double modulo' operator which is for
>> example in CoffeeScript (some discussion can be found here
>> https://github.com/jashkenas/coffeescript/issues/1971).
>>
>> This operator, unlike normal modulo, takes sign from the divisor, not the
>> dividend e.g. -10 % 3 == -1, but -10 %% 3 == 2.
>>
>> In practice, this operator is useful for 'cyclical' indexing. For
>> example, it would be useful for calculating the real index into a
>> collection when we are using an index outside of the range of valid indices
>> and could be used to index into a collection using a negative index à la
>> Python and Ruby (where [1,2,3,4][-1] == 4).
>>
>>
>> The implementation would probably be something along these lines:
>>
>> infix operator %% {
>>   associativity left
>>   precedence 150
>> }
>>
>> func %%<T: IntegerArithmeticType>(lhs:T, rhs:T) -> T {
>>   return (lhs % rhs + rhs) % rhs
>> }
>>
>> If accepted, this could be later incorporated into a method or operator
>> that works directly with collections using their count property.
>> Maybe the syntax could be something like [1,2,3,4] %% -1 == 4.
>>
>> Ideas, suggestions?
>>
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>>
>>
>
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