[Issue 15164] New: std.utf.byDchar is doing an extra popFront to its input range

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15164

          Issue ID: 15164
           Summary: std.utf.byDchar is doing an extra popFront to its
                    input range
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: blocker
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

Consider:

  import std.utf;
  import std.stdio;
  import core.stdc.stdio;

  struct S {
    bool empty() { printf("empty\n"); return !s.length; }
    @property auto front() { printf("front\n"); return s[0]; }
    void popFront() { printf("popFront()\n"); s = s[1 .. $]; }
    string s;
  }

  void main() {
    auto s = S("1 2 3");
    auto r = s.byDchar();

    r.empty;
    r.front;
    printf("end\n");
  }

which prints:

  empty
  empty
  front
  popFront()
  end

The call to popFront should not be happening. This is blocking a fix to
regression https://issues.dlang.org/show_bug.cgi?id=14861

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