import std.range;
import std.array;
struct X{
    string s;
    @property front(){
        return s.front;
    }
    @property void popFront(){
        s.popFront;
    }
    @property bool empty(){
        return s.empty;
    }
}

static assert(isInputRange!(X));



fails, though I can't for the life of me figure out why

dmd 2.047