https://issues.dlang.org/show_bug.cgi?id=24842

          Issue ID: 24842
           Summary: No ability to overload unary logial not operator
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: info@lapyst.by

Dlang has wide range support for overloading nearly all operators the language supports. However, I'm missing support for the unary logical not operator.

Usecases are implementation of (feature-)flags, or my current use-case, notation of if an certain format is allowed or not for serialization / processing. Essentially all datastuctures that are logically negateable would benefit of the ability to overload the logical not operator.

Example:
```d
struct FormatId {
    string id;
    bool allowed = true;

    this(string id) {
        this.id = id;
    }

    private this(string id, bool allowed) {
        this.id = id;
        this.allowed = allowed;
    }

    auto opUnary(string op)() if (op == "!") {
        return FormatId(this.id, !this.allowed);
    }
}

unittest {
  auto f1 = FormatId("test");
  assert(f1.allowed == true);
  auto f2 = !f1;
  assert(f1.allowed == true);
  assert(f2.allowed == false);
}
```

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