On Sep 6, 2012, at 8:39 PM, Joel de Guzman wrote:
On 9/7/2012 3:37 AM, Eric Niebler wrote:
On 9/4/2012 8:01 PM, Joel de Guzman wrote:
The question is: should we allow SFINAE for result_of. I think now that we should.
I made a case for this on the committee reflectors. They generally seem to like the idea. In short: you were right, Joel. I'm now generally in favor of changing result_of. Boost result_of can be existing practice for (hopefully) a future change in the standard. Daniel, is this something you're also interested in? I can see about a patch.
Well, I'm not sure what you have in mind, but I went ahead and fleshed out my approach from the other night. I opened a ticket (#7343) and attached a patch. It seems to work pretty well, and the test suite passes. I also added a SFINAE test derived from Joel's example to the test suite. Let me know what you think. As far as the standard, to allow a SFINAE compatible result_of implementation such as the one in my patch you would need language such as the following: If the expression decltype(INVOKE(declval<Fn>(), declval<ArgTypes>()...)) is well formed, then the member typedef type shall name the type decltype(INVOKE(declval<Fn>(), declval<ArgTypes>()...)). Otherwise, if the expression decltype(INVOKE(declval<Fn>(), declval<ArgTypes>()...)) is not well formed, the expression result_of<Fn(ArgTypes...)>::type shall not be well formed. Actually, I'm not sure if the term "well formed" is the right one here, but you get the idea.
Joel, since this is essentially your idea, would you be interested in co-authoring a paper for the committee? I don't anticipate it would have to be very long or elaborate.
It'll be an honor to co-author a paper with you.
Also, apologies for my defensiveness earlier.
No need for apologies. I just wanted to say that we need to keep a jovial spirit here in boost. We are all volunteers. We all make mistakes. Apologies for the xkcd-ish comment.
No need to apologies for xkcd-ish comments. xkcd is brilliant and the world would be a better place if we could all show such good humor and warmth. :-) - Daniel