Lorenzo Caminiti wrote:
> > read() can fail, so you can drop its "valid" precondition and just fail
> > when the handle is invalid.
>
> Calling read() on a moved-from object so violating its is_valid()
> precondition is a bug, not a run-time error while reading the file. The
> precondition legitimately remains in place to catch bugs, even after it is
> noted that read() can fail because of file-system or other run-time
> errors.
On one hand, you want to have a precondition.
On the other, you say that if you have the precondition, the class would be
crippled and not very useful:
>> 2. How useful is a class like the one above with "crippled" invariants
>> and is_valid() preconditions on all its useful public methods like
>> read()? The answer seems to be: not very useful.
These are contradictory. Either the class that has preconditions is crippled
and not very useful, in which case we drop the preconditions as I suggest;
or it's useful, in which case we keep them.
