On Tuesday, July 26, 2016 10:11:43 Bahman Movaqar via Digitalmars-d-learn wrote: > On 07/26/2016 09:35 AM, Bahman Movaqar wrote: > > I have a range which is the result of a couple of chained range > > > > operations, and each element is: > > Tuple!(string, "product", double, "price") > > > > Now I'd like to sort the range by "price" using: > > sort!((pp1, pp2) => cmp(pp1.price, pp2.price) > 0)(theRange) > > > > But I get a compile time error: > > > > source/services.d(166,63): Error: template std.algorithm.sorting.sort > > cannot deduce function from argument types !((pp1, pp2) => > > cmp(pp1.price, pp2.price) > 0)(MapResult!(__lambda5, Result)), > > candidates are: > > > > /home/bahman/Programs/D/dmd-2.071.0/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1027,1): > > std.algorithm.sorting.sort(alias less = "a < b", SwapStrategy ss > > > > = SwapStrategy.unstable, Range)(Range r) if ((ss == > > SwapStrategy.unstable && (hasSwappableElements!Range || > > hasAssignableElements!Range) || ss != SwapStrategy.unstable && > > hasAssignableElements!Range) && isRandomAccessRange!Range && > > hasSlicing!Range && hasLength!Range) > > source/services.d(168,5): Error: var has no effect in expression > > (theRange) > > dmd failed with exit code 1. > > Alright...further experiments. The following works: > > sort!((pp1, pp2) => cmp(pp1.price, pp2.price) > 0)(theRange) > > So it may be something about what kind of range I'm passing to `sort`. > Am I right?
sort requires a random access range. Without knowing exactly which algorithms your using, I can't say for sure that that's the problem, but usually it is. Most of the time, you don't end up with a random access range after chaining several range-based functions. You _can_, but it depends entirely on which functions they are and the type of your original range. It's frequently the case that if you want to sort a range, you have to call array() on it to convert it to an array, and then you can sort the array. - Jonathan M Davis
