On Friday, November 11, 2016 11:49:25 RazvanN via Digitalmars-d-learn wrote: > I am a bit confused about how the is operator works. I have a > function which receives an InputRange and a predicate. Now I need > to be able to test if the InputRange is actually a SortedRange. I > don't care about how the datatypes behind the SortedRange or the > predicate, I just need to see if the object is a SortedRange. I > have tried the following test: > > static if(is(typeof(haystack) == SortedRange!(T, _pred), T, > _pred)) > > where haystack is the InputRange, but the test fails. Is there a > way to test if the InputRange is a SortedRange without having to > explicitly pass the primitive tupe on top of which the > SortedRange is built?
The correct way to do this with an is expression is a bit esoteric, and you don't want to have to deal with it. Fortunately, someone added an appropriate trait to std.traits to do this for you: std.traits.isInstanceOf (which should arguably be called isInstantiationOf, but it is what it is): http://dlang.org/phobos/std_traits.html#isInstanceOf And by the way, what you're trying to use is an "is expression," not the "is operator." The is operator is used for doing a bitwise comparison of two objects. e.g. struct S { int i; } assert(S(5) is S(5)); or int[] arr; assert(arr is null); and it's a runtime constructor, not a compile time one, unlike is expressions. - Jonathan M Davis
