I’m not really sold on the `%%` spelling, but I think the operation itself is worth exposing. This is the remainder of a “flooring” division (as opposed to the C-family “truncating” division[1]). If we do provide it, we should also provide the accompanying divide operation.
– Steve [1] there are several other ways to define division beyond these two: remainder is always positive, remainder is closest to zero, etc. Truncating and flooring division are the most common by a wide margin, however. > On May 21, 2016, at 4:22 PM, Adam Nemecek via swift-evolution > <swift-evolution@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 > <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? > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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