Re: [boost] 3-state boolean type

From: Rob Stewart (stewart_at_[hidden])
Date: 2002-08-02 12:24:16

From: "William E. Kempf" <williamkempf_at_[hidden]>
> 
> From: "Rob Stewart" <stewart_at_[hidden]>
> 
> > It seems to me that the default ctor should initialize the state to
> > indeterminate (or whatever it will be called).  Since bool doesn't have a
> > default ctor, this is the most logical behavior for tribool.
> 
> That depends on what you mean here.
> 
> bool b;
> 
> This doesn't initialize the value for b, and thus would (fuzzily) suggest
> what you're saying.  However, this:

Indeed, that's what I was thinking.  b isn't initialized to anything known, so
it's value is, effectively, unknown or indeterminate.

> bool b();
> 
> initializes b to false.  So I'd think the  default ctor should initialize
> the state to false.

That doesn't invoke the default ctor.  You'd have to do something like this:

   bool b(bool());

to get what you're referring to.

> > I agree with the sentiments regarding the name.  Of those suggested thus
> far, I
> > like tristate.
> 
> I'd call it logic_state.  A value of 0 would indicate false, a value of 1
> would indicate true, and any other value would be "indeterminate", giving
> you the multiple "indeterminate" states people have suggested.  Of course
> you could templatize this so that logic_state could specify the number of
> indeterminate states.  As for symbolic names... I wouldn't specify any, and
> let the user specify the ones that fit his domain.  Alternatively, you could
> specify one or more well known sets of symbolic names, such as the suggested
> bottom.

This in an interesting approach.  I could see it being implemented with a char
-- or other parameterized integer type -- with distinct true and false values,
plus a range of other legal values in between.  Based upon what you're saying,
the other values can then be named externally; the names needn't be part of the
class.  That seems like it is workable without being unwieldy.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;