Re: [Boost-users] Library Interface Design

From: David Abrahams (dave_at_[hidden])
Date: 2006-09-14 07:05:53

Scott Meyers <usenet_at_[hidden]> writes:

> Marshall Clow wrote:
>> At 9:06 PM -0700 9/13/06, Scott Meyers wrote:
>> [ snip ]
>>> I'll note that C++ itself allows "uninitialized" objects with
>>> constructors to be created all the time:
>>>
>>>    std::ofstream ofs;
>>>    std::vector<int>::iterator i;
>>>    std::string s;
>> 
>> Just a nit - I think that your third example is not like the others.
>> A std::string, AFAIK, constructed with the default constructor, is 
>> perfectly valid - just empty.
>
> In each case, a default constructor is invoked.  They're all valid 
> objects that presumably fulfill their invariants, it's just that you 
> can't safely invoke very many operations on them.  On the string s, for 
> example, invoking size is fine, but invoking operator[] is not fine at all.

The difference is that there are no special cases in the specification
of std::string to cover the default-constructed case.  The other two
may fall within the invariants, but they're degenerate objects
requiring special consideration.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com