On Wednesday, May 25, 2016 15:05:33 qznc via Digitalmars-d wrote: > Today I learned [0] that opDollar must be explicitly implemented > and might not be available by some ranges. Likewise slicing. If > you think it further, there are lots of functions in Phobos (I'm > currently looking into std.algorithm.searching) which use more > features than they check capabilities for. Ranges which satisfy > isRandomAccessRange do not automatically satisfy hasSlicing. > > Can we provide opSlice and opDollar implicitly for random access > ranges? > > Alternatively, we should comb through Phobos to fix the > capability checks and write unittests with minimalistic ranges. > > I already filed issue 16073 [1], but then realized it does not go > far enough. > > Also, std.range.primitives should have a predicate for opDollar > similar to hasSlicing. > > [0] https://github.com/dlang/phobos/pull/4362#discussion_r64576690 > [1] https://issues.dlang.org/show_bug.cgi?id=16073
hasSlicing and isRandomAccessRange do require that opDollar work correctly if they're there, but it would have been way too large a breaking change to make them require opDollar, and it's kind of silly to make them implement opDollar when the compiler could generate for them from length, which is why https://issues.dlang.org/show_bug.cgi?id=7177 exists. Unfortunately, it's never been implemented (IIRC due to issues related to AAs having length but not being ranges; the implementation likely needs to check for the range-based functions in addition to length). And as long as 7177 hasn't been implemented, hasSlicind and isRandomAccessRange can't require $, and until they require opDollar, Phobos should never use $ on ranges unless they're guaranteed to be arrays or guaranteed to be ranges that implemented opDollar, and that's really true of _any_ D code at this point, not just Phobos. IMHO, we really should implement some form of 7177 so that we can actually make it possible to use $ with ranges, but until that happens, we're out of luck. - Jonathan M Davis
