Re: [boost] [signals2] Test failure in C++11 (trivial fix for incorrect usage of boost::optional)

On Fri, Feb 28, 2014 at 7:38 PM, Frank Mori Hess wrote:

On Thu, Feb 27, 2014 at 8:45 PM, Gavin Lambert wrote:

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On 28/02/2014 12:33, Quoth Frank Mori Hess:

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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.

I don't think I agree with that. IMO, "x==false" should not compile since it has ambiguous interpretation.

neutral behavior: only one compiles.

This one is desirable for me.

undesirable behavior: they both compile and mean completely different things.