How to overcome overloading ambiguity

"Fred Zwarts" <>
Tue, 16 Jun 2009 11:36:57 +0200
In my software I need a vector of boolean values.
My first attempt was to use vector<bool>, but vector has a =
specialization for the bool type
with unwanted implications. For example, I need to pass elements of the =
vector as
reference to bool (bool&) to certain functions which may modify the =
value of such elements.
This is not possible with vector<bool>.

My next idea was to create a class Boolean_t which can be used instead =
of the bool type,
with transparent functionality. So I attempted the following:

class Boolean_t {
  bool Flag;


// Normal constructor:

  Boolean_t (const bool InitialValue = false) : Flag (InitialValue) {}

// Define conversion to bool and reference to bool.

  operator bool () const {
    return Flag;

  operator bool & () {
    return Flag;

My problem is with two operator definitions. I need both.
The first one is needed to convert a const object to a bool value,
which cannot be done with the second one.
The second one is needed to pass objects of type Boolean_t to functions =
that need a reference to bool,
which cannot be done with the first one.

However, if an object of type Boolean_t is used in a boolean expression, =
the compiler complains
about an ambiguity in the reference to a conversion function. Indeed, I =
understand that both
of these conversion functions could be used in this case.
Is there a solution to overcome this ambiguity and to keep the =

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