On Thu, Feb 27, 2014 at 8:45 PM, Gavin Lambert
On 28/02/2014 12:33, Quoth Frank Mori Hess:
Ah, I wasn't aware optional already had overloaded the comparison operators with comparisons of optional<T> vs T. A little unfortunate IMO, it makes optional<bool> a bit of a disaster when any sort of conversion to bool at all is supported.
Not really; tristate bool logic with optional<bool> is pretty straightforward. It usually falls into the pattern:
if (value == true) { /* do something when true */ } else if (value == false) { /* do something when false */ } else { /* do something when null/none/unknown/unspecified */ }
There is a little trap for the unwary where:
if (value) { /* either true or false */ } else { /* only null, not false */ }
But once you get used to it, I'd hardly call it a "disaster".
Nothing is a problem once you get used to it. I apologize for using a bit of hyperbole, let me try again. I consider the following obvious: given two expressions like "!x" and "x==false" we have: desirable behavior: they both compile and mean the same thing. neutral behavior: only one compiles. undesirable behavior: they both compile and mean completely different things. -- Frank