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"Ambiguous resolution" error from selective constructor inheritance

The second candidate is probably the implicitly-defined copy-assignment operator, which is not shown in the source code so the compiler points to the class itself.

Your Long class has an implicit conversion to various integer types that are convertible to bool and those types are also convertible to Boolean, and both of those types can be assigned to a Boolean, so the compiler doesn't know which to convert to before performing the assignment.

You could make the conversion explicit so the compiler doesn't need to check:

b = bool(l);

or equivalently, but more explicitly (and maybe more clearly for some readers):

b = static_cast<bool>(l);

You probably want to avoid too many explicit conversions between types, it gets confusing and leads to these sort of problems. To disable implicit conversion and require explicit casts to tell the compiler what conversions you want to perform, either make converting constructors explicit, or make the conversion operators explicit (or both).

Categories : C++

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